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allocation of floor area to function of housing

Minimum Spatial Housing Requirements for Human Flourishing

Karl T. Ulrich

University of Pennsylvania. The Wharton School. Operations, Information, and Decisions Department, Philadelphia, PA 19104, USA

KT Ulrich. Minimum Spatial Housing Requirements for Human Flourishing. Buildings. 2025. Volume 15.
(full text below PDF)

Abstract

This study defines evidence-based minimum internal floor areas required to support long-term residential use across different household types. It addresses the following question: what is the smallest viable floor area that supports sustained occupancy without persistent stress, conflict, or turnover? An integrative review method was employed, drawing from behavioural studies in environmental psychology, international regulatory standards, and real-world market data. The analysis focuses on essential domestic functions including sleep, hygiene, food preparation, storage, social interaction, and work. Quantitative findings from tenancy surveys, post-occupancy research, and market performance data indicate that residential units below 30 square metres for single occupants and 45 square metres for couples are consistently associated with reduced satisfaction and shorter tenancies. Regulatory minimums across diverse jurisdictions tend to converge near these same thresholds. The study proposes technical minimums of 30, 45, and 60 square metres for one-, two-, and three-person households, respectively. These values reflect functional lower bounds rather than ideal or aspirational sizes and are intended to inform performance-based housing standards.

Keywords: minimum home size; affordable housing; floor area; unit size; housing standards; micro housing; nano housing; tiny homes

1. Introduction

In the face of a global affordability crisis, housing systems increasingly rely on compact dwellings to expand supply in urban areas. However, the pursuit of higher densities and lower construction costs often proceeds without robust empirical guidance on how small is too small. While attributes such as energy efficiency, structural integrity, and environmental impact are routinely measured and regulated, internal floor area, the most fundamental spatial parameter of dwelling performance, is inconsistently addressed in most building codes [1,2].

A growing body of research suggests that below certain spatial thresholds, residential dwellings may no longer support the basic conditions for health, autonomy, and psychological well-being. Evidence from environmental psychology, building design, post-occupancy studies, and housing markets points to consistent patterns in how households respond to limited living space. These include rising levels of stress, shorter tenancy durations, reduced satisfaction, and increased rates of residential turnover [3–5].

This paper addresses the following central research question:

What is the minimum internal floor area required for a housing unit to support long-term human flourishing?

To answer this question, the study draws on evidence from multiple domains, including environmental psychology, regulatory frameworks, and market behaviour. Rather than focusing on average or desirable housing sizes, it aims to identify the technical and functional minimum: the smallest internal floor area that allows a household to carry out essential domestic activities over time without persistent stress, conflict, or risk of displacement.

Recent policy developments and market research reinforce the urgency of establishing empirically grounded spatial minimums. The 2025 update to the UK national space standards affirms 37 square metres as the lowest acceptable internal area for a single-person dwelling, reflecting a continued reliance on point-value thresholds in regulatory guidance [6]. Recent analysis of English space standards reveals ongoing tensions between affordability pressures and adequacy requirements in social housing provision [7]. In North America, compact living is increasingly framed as a mainstream strategy for achieving affordability and urban density [8]. Empirical evidence from land-use reforms shows that relaxing regulatory constraints can increase available living space while reducing per-unit cost burdens [9]. These developments underscore the need to define lower spatial bounds using behavioural and functional indicators, not solely historical precedent or policy negotiation.

This study differs from previous work by focusing not on average or desirable unit sizes, but on identifying functional lower bounds for long-term residential use. While many studies explore housing quality, affordability, or density in isolation, few integrate evidence across behavioural psychology, regulatory standards, and market performance to define minimum viable space. This triangulated approach yields floor area thresholds that are both technically grounded and practically relevant. By aligning spatial adequacy with real-world behaviour, the findings offer a performance-based framework that can inform policy, design, and code development in diverse contexts.

1.1. Supporting Questions and Policy Relevance

In identifying these minimum floor area thresholds, the study also explores several supporting questions:

  • What are the spatial requirements for core domestic functions such as sleep, hygiene, food preparation, storage, social interaction, and remote work?
  • How do regulatory standards for minimum dwelling size vary across jurisdictions, and how well do they align with behavioural and psychological evidence?
  • What does market behaviour reveal about the practical limits of compact housing, especially in high-cost urban environments?
  • At what point does spatial inadequacy lead to measurable declines in satisfaction, tenure stability, or mental health?

These questions have direct implications for several pressing housing challenges. Among them are:

  • What is the lowest feasible cost for delivering liveable housing at scale?
  • How much residential floor area is required to support a given urban population within environmental constraints?
  • What unit sizes are most appropriate for modular and prefabricated housing systems?
  • How should housing standards evolve to address the rise in single-person households and the increasing prevalence of remote work?

None of these issues can be addressed meaningfully without a baseline understanding of how much space people need, at a minimum if not an ideal, to sustain daily life in a stable, healthy, and autonomous manner.

1.2. Global Household Size and Composition: A Foundation for Space Standards

Average household size has fallen worldwide for more than four decades. United Nations data show a decline from approximately 4.9 persons per household in 1980 to about 4.0 in 2020, with the median country now near or below four persons [10,11]. The trend is especially pronounced in high-income economies. The OECD reports a current average household size of 2.4 persons, with more than one third of member countries now composed primarily of one- and two-person households [12,13].

Rapidly ageing East Asian societies display the same pattern. Japan’s 2020 census records 2.3 persons per household nationally and 1.9 in the Tokyo metropolitan core [14]. South Korea reports 2.2 persons nationwide and fewer than 2.0 in Seoul [15].

Small households already dominate urban housing demand. Across large European metropolitan areas, single-person dwellings account for 35 to 45 percent of occupied units, while two-person households add another 30 to 35 percent [13]. United Nations Habitat analysis finds a similar structure in rapidly urbanising regions of Latin America and East Asia, although three-person households remain slightly more common there [16]. Table 1 summarises these proportions and links them to their principal drivers: population ageing, delayed marriage, declining fertility, and the rise in solo living among both younger and older adults [17,18].

Table 1 . Three Size Categories of Households.

Household TypeEstimated ShareTrendDemographic BasisDesign Relevance
Single-Person28–35%Strongly
increasing
Ageing, urban migration, autonomyMost common compact unit
Two-Person32–38%IncreasingCouples without children, retireesKey transitional household
Three- to Four-Person30–35%Stable/DecliningNuclear families, emerging middle classCore benchmark for family units

Multigenerational and group households continue to be significant in parts of Africa, South Asia, and the Middle East, yet their spatial requirements differ enough to warrant separate treatment later. For the compact-dwelling typology that follows, the focus remains on one- to four-person nuclear households, which represent the bulk of future housing demand in urbanised regions.

1.3. Methodological Approach

This study uses an integrative review methodology to identify evidence-based minimum internal floor areas suitable for long-term residential use. The aim is to synthesise findings from multiple domains, including environmental psychology, building regulation, and housing market behaviour, to establish the functional lower bounds of spatial adequacy. An integrative review is appropriate in this context because the evidence base includes both peer-reviewed research and grey literature and spans diverse methodological formats [19].

The analysis proceeded in three phases. First, spatial requirements for core domestic functions were identified from studies in environmental psychology, ergonomics, and post-occupancy evaluation. These functions include sleeping, hygiene, food preparation, social interaction, storage, and remote work. Second, national and local building codes were reviewed to assess formal minimum size requirements. Sources included official building standards, planning documents, and housing regulations across multiple jurisdictions. Third, market typologies and occupancy outcomes were examined in cities where compact dwellings are widely built and occupied. Data sources included tenancy duration surveys, resident satisfaction reports, real estate market analyses, and public-sector housing datasets.

Findings from the three domains were organised using a comparative matrix. Where psychological thresholds, regulatory minimums, and observed market behaviour consistently aligned, a floor area threshold was proposed. These proposed values are defined as technical lower bounds for sustained residential use. They are not intended as normative goals or average sizes.

Because the study integrates both academic and non-academic materials, no systematic keyword protocol or database screening process was used. Sources were selected for empirical specificity (such as quantified thresholds for domestic activities), jurisdictional diversity (including regulatory frameworks from multiple continents), and conceptual relevance to spatial sufficiency and long-term residential stability. The review drew from more than 100 documents, including peer-reviewed studies, government standards, industry reports, and post-occupancy surveys. Although no formal date cut-off was imposed the majority of sources were published after 2000, with priority given to post-2010 studies where available. This flexible approach supports evidence-informed design and policy decisions where minimum standards must be reconciled with lived outcomes.

2. Spatial Requirements for Well-Being and Function

A building’s spatial adequacy is a key component of its performance. While regulatory minimums and market behaviour often reflect political compromise or economic constraint, they do not necessarily ensure long-term psychological comfort, physical health, or functional usability. This section synthesises research from environmental psychology, ergonomics, post-occupancy evaluation, and time-use studies to identify the threshold at which housing space continues to support core human activities and enables flourishing. These insights inform our proposed floor area minimums by grounding them in behavioural and functional performance rather than availability, aesthetics, or tradition. A growing body of research has examined the relationship between spatial parameters and occupant well-being at the urban and building scale [20–22]. However, these studies primarily focus on external or neighbourhood-scale spatial qualities, whereas this work addresses the spatial adequacy of the home itself.

2.1. Crowding, Density, and Psychological Stress

Crowding refers to the subjective experience of having insufficient personal space, while density refers to the number of people per unit area. Studies consistently show that it is perceived crowding, not density alone, that predicts negative psychological outcomes [21]. Evans et al. [3] found that residential crowding, often defined as fewer than 15–20 square metres per person or more than one person per room, is associated with chronic stress, cognitive delays in children, and elevated cortisol levels. These psychological impacts can be quantified using established well-being valuation methodologies [23,24], enabling systematic assessment of housing adequacy’s broader social costs. These effects tend to occur once space drops below key thresholds, suggesting the presence of spatial tipping points in psychological resilience.

Research on social housing in Great Britain provides additional evidence of these threshold effects. Hickman [25] demonstrates that inadequate housing conditions significantly impair residents’ ability to maintain social connections and access “third places” for community interaction, with spatial constraints being a key factor in social isolation. Furthermore, longitudinal studies of tenancy sustainment reveal that housing inadequacy, including insufficient space, is strongly associated with tenancy breakdown and residential instability [26]. These findings reinforce the importance of establishing evidence-based spatial minimums that support not only individual well-being but also community cohesion and housing stability.

2.2. Privacy, Control, and Territorial Function

The ability to regulate one’s environment through visual, acoustic, and spatial boundaries is central to housing performance. Ozaki and Lewis [27] identify four domains of privacy: personal, informational, territorial, and acoustic. When these are compromised, occupants report increased psychological distress and decreased satisfaction. Kopec [28] finds that households in compact units often struggle to maintain behavioural autonomy, particularly in relation to partners or children. Our synthesis suggests that below 30 square metres for single adults and 45 square metres for couples, housing units frequently fail to support the full range of privacy functions, even with good design.

2.3. Activity-Based Space Requirements

Post-occupancy evaluations and time-use studies offer detailed insight into the spatial requirements of essential domestic activities. While cultural context and layout quality affect thresholds, certain space needs recur across geographies and dwelling types.

  • Sleeping typically requires 5 to 7 square metres per person, accounting for bed size, circulation, and storage. A single bed with access on one side requires approximately 4.5 square metres, while a double bed needs 6 to 8 square metres for comfort [29,30].
  • Food preparation and dining require a minimum of 4 to 6 square metres per household. Research on kitchen ergonomics shows that functionality depends more on workflow efficiency than household size [31,32]. Kitchens smaller than 3.5 square metres are associated with reduced satisfaction and increased time inefficiency [33].
  • Hygiene facilities require 3 to 4 square metres to comfortably accommodate toilet, basin, and shower fixtures. Although compact bathrooms can function in as little as 2.5 square metres, users consistently prefer bathrooms of at least 3.5 square metres for comfort and accessibility [29].
  • Socialising and relaxation typically require 7 to 12 square metres, depending on household size. Single-person households can function with 6 to 8 square metres for a small seating area and media use, while larger households require more space to accommodate multiple users simultaneously [34,35].
  • Work or study requires 2 to 3 square metres per working occupant. This accommodates a desk, task chair, and minimal storage. Spaces below 2 square metres are associated with reduced productivity and increased fatigue [36–38].
  • Storage needs average 3 to 4 square metres per person, including space for clothing, equipment, seasonal items, and household supplies. When this falls below 2.5 square metres per person, spatial disorder and visual clutter increase significantly [29,39,40].

When units fall below these thresholds, “activity compression” occurs. In these cases, essential tasks begin to overlap or displace one another as follows: sleeping occurs in living spaces, eating happens on beds, or work is done in hallways. Bratt [41] describes how such compression can degrade usability and lead to residential dissatisfaction. Lawrence [42] and Després [43] emphasise that these spatial compromises are not just inconvenient, but symbolically and psychologically disruptive. Over time, the cumulative effect of compressed or improvised functions erodes the domestic environment’s ability to support stability, identity, and autonomy.

2.4. Adaptation and Design Moderators

Residents employ a variety of coping strategies in very small dwellings. Temporal zoning, selective use of common areas, personalisation of limited surfaces, and cognitive reframing can all moderate the feeling of crowding [44]. High ceilings, abundant daylight, generous built-in storage, and carefully framed views increase perceived spaciousness and postpone fatigue. Even so, longitudinal evidence shows that adaptation has clear limits once floor area drops below roughly twenty square metres per person.

Several dense-city studies illustrate those limits. In Hong Kong, sixty per cent of households occupying flats smaller than twenty-five square metres rate their living space as unsatisfactory, and a majority intend to relocate within two years [45,46]. In Tokyo, micro-apartments under twenty square metres support average tenancies of only 1.8 years, whereas similar buildings with twenty-five square metres or more achieve average stays of 3.2 years [47]. Hong Kong turnover is likewise highest in nano-flat households that share less than twenty square metres per person [5]. Mumbai surveys show a parallel pattern, with dissatisfaction and intent to exit rising sharply after twelve to eighteen months in eighteen to twenty-five square metre “nano homes” [48].

Good design can reduce noise, create visual depth, and provide multi-functional furniture that stretches usability for short periods; however, extended residence below the twenty-square-metre threshold consistently produces higher stress, clutter, and social friction. Across cases, ingenuity and supportive management can delay but not eliminate the physiological and psychological burdens imposed by extreme spatial constraint.

2.5. Cultural Modifiers of Spatial Expectation

Cross-cultural research shows that acceptable space standards vary with social norms, and that urban context, including spatial parameters of neighbourhoods and access to green spaces, also significantly affect well-being [22,49]. East Asian residents, for example, often rate smaller units as acceptable due to norms of compact living, floor-sitting, and shared public amenities. Ozaki and Lewis [27] found that Japanese households consider 20% less space acceptable than matched British counterparts. However, Whiteford and Hoff [50] show that all cultures share basic needs for control, quiet, and autonomy, indicating that minimums can vary slightly but not be abandoned altogether.

2.6. Children and Developmental Needs

Children are particularly sensitive to spatial inadequacy. Overcrowded homes (under 8 m2 per child) are linked to lower academic performance, behavioural problems, and impaired sleep [51]. Developmental needs include quiet study space, physical separation for sleep, and play areas. These requirements support higher minimums for family dwellings.

2.7. Remote Work and the New Domestic Function

Post-pandemic housing must now accommodate remote work as a standard rather than exceptional domestic function. The rapid shift to home-based work has fundamentally altered spatial requirements, with implications for minimum housing standards that previously assumed work occurred outside the dwelling unit.

Effective home workspaces require an additional 3–5 m2 per worker beyond traditional residential functions, with minimum dimensions of 1.2 m × 1.5 m[M18] [KU19]  to accommodate desk, chair, and equipment storage [52,53]. This represents a 15–20% increase in space requirements for households with remote workers. Studies of telework environments indicate that workspaces below 2.5 m2 per user result in reduced productivity, increased physical discomfort, and higher rates of work-related stress [54,55].

The quality of home workspace significantly affects both work performance and residential satisfaction. Research during COVID-19 lockdowns found that lack of dedicated workspace in units under 30 m2 was strongly associated with depressive symptoms, anxiety, and decreased job satisfaction [56,57]. Workers in compact housing without defined work zones reported difficulty maintaining work–life boundaries, leading to extended working hours and reduced recovery time [58].

Work zones must be visually and acoustically distinct from other domestic functions to support cognitive performance and psychological boundaries [59,60]. Open-plan arrangements where work occurs in living or sleeping areas show measurably lower task performance and higher stress indicators compared to spatially separated workspaces [61,62]. Even temporary visual barriers or acoustic separation can improve work effectiveness in constrained spaces [63,64].

Ergonomic requirements for sustained computer work, including proper desk height (72–76 cm), chair clearance (minimum 60 cm behind desk), and screen distance (50–70 cm), establish minimum spatial envelopes that cannot be compressed without health consequences [65,66]. Studies of home-based workers show increased musculoskeletal problems when workspace dimensions fall below ergonomic minimums [67,68].

The acoustic environment proves equally critical for remote work functionality. Research indicates that background noise levels above 50 dB significantly reduce cognitive performance and increase fatigue in knowledge work [69,70]. Compact housing often struggles to provide acoustic separation between work and domestic activities, particularly in units below 40 m2 where spatial buffering is limited [71].

Storage requirements for work equipment add approximately 0.5–1 m2 per remote worker, including space for technology, documents, and professional materials that cannot be integrated with household storage [52,72]. Inadequate work storage leads to spatial spillover that compromises both work efficiency and domestic function.

These findings suggest that housing units intended to accommodate remote work require baseline increases of 20–25% over pre-pandemic spatial standards. For single-person units, this elevates functional minimums from approximately 25 m2 to 30 m2, while couple units require approximately 45 m2 to maintain both residential quality and work functionality. Units that cannot accommodate these expanded requirements may function for short-term residence but prove inadequate for sustained occupancy in an economy increasingly dependent on home-based work.

The thresholds identified in behavioural and post-occupancy research provide a functional basis for determining spatial adequacy. These findings set reference points for evaluating whether existing regulations reflect the space required to support long-term residential well-being. The next section surveys regulatory standards to assess how policy frameworks correspond to the evidence on domestic activity needs and psychological thresholds.

3. Global Regulatory Standards and Spatial Minimums

While spatial adequacy is grounded in functional and behavioural needs, housing regulations set the operational boundaries for what can be legally built. This section reviews regulatory minimum dwelling sizes across diverse jurisdictions to assess the extent to which existing standards align with or diverge from empirically defined spatial thresholds.

3.1. Regulatory Diversity and Spatial Baselines

Minimum dwelling-size rules differ sharply from one world region to the next. A west-to-east review, following the ordering in Table 2, highlights both the variety of legal instruments and the narrow band into which many numeric thresholds ultimately converge. Recent analyses underscore the need for clearer alignment between minimum standards and lived spatial needs, especially in the context of regulatory reforms in East Asia [73].

North America begins with a code baseline rather than a whole-unit floor. All fifty US states adopt the International Building or Residential Code, whose only size mandate is a habitable room of at least 11 m2; every dwelling must contain at least one such room [74]. Canada’s Ontario Building Code raises that figure to 13.5 m2 for a living room, while most bedrooms must be at least 7 m2 [75]. Large Canadian cities then overlay per-person limits: Toronto requires a minimum of 9 m2 of usable floor area for each adult occupant, enforceable through its property-standards by-law [76]. In short, North American regulation relies on room-by-room rules or occupancy caps rather than a fixed flat-size plateau.

Latin America and the Caribbean show a split between market housing and social-housing programmes. Mexico City’s 2018 construction code sets a statutory lower bound of 25 m2 net floor area for any new apartment, giving the region’s most compact private-sector limit [77]. Brazil and Chile impose larger figures but only where federal or national subsidies are involved: Brazil’s relaunched Minha Casa Minha Vida requires 41.5 m2 for an apartment and 40 m2 for a single-family house [78], while Chile’s DS-49 programme mandates 40 m2 for subsidised dwellings [79]. Outside those programmes, private developments can be smaller.

Europe embeds minimums directly in national legislation but uses two distinct logics. England fixes a studio plateau of 37 m2 gross internal area through the Nationally Described Space Standard [80]. Sweden’s building code recognises 35 m2 as the lower limit for a self-contained unit because many accessibility concessions apply only when the dwelling is larger [81]. Germany, France, and the Netherlands regulate crowding instead: Germany’s Länder bar lettings that fall below about 9 m2 per adult [82], France requires 14 m2 per person for the first four occupants [83], and the Dutch Bouwbesluit demands at least one living area of 18 m2 in every dwelling [84]. Despite different metrics, these rules cluster between 35 m2 for a single occupant and 14–18 m2 per person in multi-person units.

Africa combines per-room codes with programme minima. Kenya’s draft National Building Code sets 7 m2 usable floor area for every habitable room, creating a practical lower bound for one-room units if the draft is adopted [85]. Lagos State’s planning standards require 10.8 m2 for each habitable room, slightly higher than Kenya’s figure [86]. South Africa’s subsidy programme for Reconstruction and Development Programme housing mandates 40 m2 gross floor area for a detached house, but that rule applies only to publicly funded units [87].

South Asia shows a single national guideline. India’s Affordable Housing in Partnership scheme fixes 25 m2 carpet area as the minimum self-contained dwelling that can receive central subsidy; states vary in their own policies, with some (for example Maharashtra) raising the floor to about 27 m2 [88].

East and Southeast Asia illustrate every tool in the regulatory toolbox. Japan’s Building Standards Act sets no flat-size floor but insists every habitable room be at least 7 m2 internal area [89]; one-room apartments therefore start at that point but market practice in Tokyo rarely goes below 15 m2 [90]. Hong Kong imposes a 26 m2 saleable-area minimum on all new private projects through land-lease conditions, while its public-rental sector follows a 7 m2 per-person allocation rule [91]. Singapore limits private and public studios outside the central area to 35 m2 gross floor area [92]. Mainland China’s national design code fixes 22 m2 usable floor area for a self-contained dwelling, though some provinces accept smaller single-occupant units [93]. Together these standards span a range from per-room minima (Japan) to whole-unit floors that rise from 22 m2 in China, through 26 m2 in Hong Kong, to 35 m2 in Singapore.

Table 2. Standards for minimum housing size by region.

RegionJurisdictionMin. Size (m2)
(Dominant
Household)
Metric †Enforcement ‡SectorSources
North AmericaUnited States (IBC/IRC model code)11 m2
(one-room dwelling)
IFASPrivate[74]
 Canada—Ontario Building Code13.5 m2
(living room)
IFASPrivate[75]
 Toronto (Property Standards)≥9 m2/personIFAAPrivate/Public[76]
Latin America and CaribbeanMexico—Mexico City Construction Code25 m2
(dwelling)
IFASPrivate[77]
 Brazil—Minha Casa Minha Vida (programme)41.5 m2 (apartment);
40 m2 (house)
IFAAPublic programme[78]
 Chile—DS49 Social Housing (programme)40 m2 (dwelling)IFAAPublic programme[79]
EuropeUnited Kingdom37 m2
(1 person, 1-storey)
GIASPrivate[80]
 Sweden35 m2 (1 person)GIASPrivate[81]
 Germany≥9 m2/personIFASPrivate[82,94]
 Netherlands18 m2
(living-space benchmark)
IFASPrivate[2,4,95]
 France14 m2/person
(≤4 persons)
IFASPrivate[83]
AfricaKenya—National Building Code 2024 (draft)7 m2/habitable roomIFAS
(draft)
Private[85]
 Nigeria—Lagos State10.8 m2/habitable roomIFASPrivate[86]
 South Africa—RDP Housing Norm40 m2
(subsidised house)
GFASPublic programme[87]
South AsiaIndia—Affordable-Housing Guidelines25 m2 (dwelling)CAAPublic–private[88]
East and Southeast AsiaTokyo (Japan)7 m2/habitable roomIFASPrivate[89]
 Hong Kong26 m2 (flat)SALPrivate[91,96
 Singapore35 m2 (studio)GFASPrivate[92]
 Mainland China22 m2 (dwelling)IFASPrivate[93]
OceaniaAustralia—New South Wales35 m2 (studio)IFASPrivate[97]
 New Zealand—Auckland Unitary Plan35 m2
(self-contained unit)
GFAZPrivate[98]

Metric codes—IFA = internal floor area; SA = saleable area; GIA = gross internal area; CA = carpet area; GFA = gross floor. ‡ Enforcement codes—S = statutory building/planning rule; L = mandatory land-lease/development agreement; A = administrative guideline or allocation rule; Z = zoning overlay.

Oceania closes the sweep with parallel state and city-level rules. New South Wales requires 35 m2 internal floor area for a studio and larger plateaus for bigger flats, a template most Australian jurisdictions now follow [97]. New Zealand’s Auckland Unitary Plan adopts the same numeric threshold, 35 m2 gross floor area, for any self-contained dwelling in the city’s medium-density zones [98].

Despite wide variation in enforcement tools, including statutes, land-lease clauses, programme rules, and zoning overlays, the numeric floors for long-term single occupancy cluster between 22 m2 and 37 m2, with many jurisdictions converging on the 30–35 m2 band. Where standards are expressed per person, figures fall between 7 m2 and 14 m2, again bracketing the 10 m2 mark. These convergences support the minimum thresholds advanced later in this paper while also revealing the political and economic pathways by which different societies pursue spatial adequacy.

3.2. Historical Patterns and Regulatory Evolution

Minimum space rules first appeared in nineteenth-century public health reforms that targeted overcrowded tenements in rapidly industrialising cities. Early by-laws in London, such as the 1890 Housing of the Working Classes Act, and New York’s 1901 Tenement House Act emphasised daylight, ventilation, and a minimum cubic volume of air per person [99,100]. After the Second World War, the welfare-state consensus encouraged many countries to adopt far more generous space norms. In England, the Parker Morris standards required about eighty-eight square metres for a four-person dwelling along with detailed room and storage requirements [101]. Sweden’s Million Programme of 1965–1974 pursued a comparable goal, producing large, well-equipped flats that averaged more than thirty square metres per person [102].

Fiscal restraint and deregulation in the late 1970s and early 1980s reversed this expansion. The Parker Morris requirements, mandatory for public housing since 1967, were formally withdrawn in 1980 as part of wider expenditure cuts [103]. Similar retrenchment occurred in Australia, Canada, and parts of continental Europe, leading to divergent national standards and shrinking average unit sizes during the 1980s and 1990s.

Since the early 2000s governments have renewed interest in minimum spatial benchmarks, driven by housing affordability crises, demographic change, and growing evidence that extreme compactness harms well-being. England adopted the Nationally Described Space Standard in 2015, restoring a minimum of thirty-seven square metres for a one-person one-storey dwelling [80]. Mexico City introduced a twenty-five square metre minimum in 2018 [77], and Hong Kong recently decided that new private flats under public land lease must not be smaller than twenty-six square metres [91]. The post-war expansion, subsequent rollback, and recent re-regulation illustrate how space standards respond to shifting social priorities as much as to technical or market constraints.

4. Revealed Preferences in Space-Constrained Markets

While regulatory standards establish what may be built and behavioural studies indicate what ought to be optimal, the lived experience of residents in compact dwellings shows the practical limits of spatial sufficiency. Observed occupancy behaviour—including tenancy duration, mobility patterns, satisfaction levels, and housing-application choices—supplies a form of revealed preference that complements normative frameworks. In the highest-cost urban markets, where land is scarce and demand intense, dwellings are routinely produced and occupied close to the lower spatial thresholds. These situations show not only what households tolerate but also when they decide to leave, adapt, or forgo particular housing options entirely.

In Hong Kong, flats smaller than forty square metres represented about one fifth of all private sales between 2019 and 2021 [104]. Micro-units of fifteen to twenty square metres are now a recognised market segment for single professionals and investors. Multiple studies document low satisfaction in such dwellings: a survey of subdivided-unit tenants found pervasive stress, health complaints, and strong intentions to relocate [46], while another study reported that sixty percent of residents in units below twenty-five square metres described themselves as “unsatisfied” or “very unsatisfied” with living space [45] (Lau & Wei, 2018). Dissatisfaction intensifies when more than one person shares these micro-flats [105].

Tokyo displays a similar pattern in its “one-room mansions,” typically fifteen to twenty-five square metres and roughly a third of the central-city rental stock. Although prized for location and efficiency, these units are mostly occupied by students and early-career professionals. Data show that apartments below twenty square metres support average tenancies of just 1.8 years, whereas those above twenty-five square metres average 3.2 years [106].

In New York City, the adAPT NYC pilot introduced twenty-four to thirty square metre studios featuring integrated storage and convertible furniture. Initial surveys recorded positive evaluations, yet a follow-up by the city’s housing department found that nearly half of occupants sought larger homes within eighteen months, especially after remote work became common [107]. London’s new co-living schemes, offering private rooms of twenty-four to thirty square metres with shared amenities, function mainly as stop-gap housing for mobile professionals, with average stays of eight to fourteen months [108].

Singapore presents a mixed public–private picture. Government-built studio flats of thirty-five square metres maintain overall satisfaction above ninety percent, although the most frequently cited reason for intending to move is the desire for more personal space [109]. In the private sector, so-called “shoebox” apartments of thirty-five to forty-five square metres attract single residents, yet market surveys indicate that more than one third of prospective buyers see lack of space as the main push factor [110].

Emerging-market cities employ compact housing as an affordability strategy. In Mumbai, “nano homes” of eighteen to twenty-five square metres target lower-middle-income singles; sixty-five percent of single buyers in a 2020 study accepted such units, but only thirty-one percent of couples found them viable [111]. São Paulo offers ten to fifteen square metre micro-apartments for mobile professionals, with average occupancy of eleven months [112]. South-African surveys show that single or childless adults will accept twenty-five to thirty square metres if build quality is high, whereas households with children express dissatisfaction below fifty square metres [113].

Across these cities, one pattern recurs. Single-person households are more tolerant of spatial constraints than couples or families, but only up to roughly thirty square metres. Tenancy duration rises by about one year for each additional ten square metres between fifteen and forty square metres [5,106]. Units smaller than twenty-five square metres exhibit sharply higher turnover, especially when occupied by more than one person.

Cultural differences shape how space is perceived, yet they do not erase the underlying tolerance thresholds. Japanese households may consider about twenty percent less space acceptable than British counterparts [27], and residents in Seoul or Hong Kong may normalise tighter dwellings. Nonetheless, units below twenty square metres consistently trigger stress, intent to relocate, and functional strain when more than one person is present [49,50].

Market data reinforce these behavioural findings. Rents per square metre rise steeply once units exceed twenty-five square metres in markets such as Hong Kong and Tokyo [5,90]. Application patterns also reveal preferences: in Singapore, studio flats of thirty-five square metres attract longer waiting times than forty-five square metre one-bedrooms despite higher total prices [109]. New York micro-units draw forty percent fewer lottery applications per available unit than conventional one-bedrooms [114].

Together, these cases underline the convergence of behavioural, economic, and cultural indicators. For single occupants, around thirty square metres is broadly viable. For two-person households, the floor rises to about forty-five square metres. Below these thresholds, dissatisfaction, early turnover, and lower application demand signal that a critical spatial limit has been breached. Compact units smaller than thirty square metres can serve short-term or transitional roles, but long-term stable occupancy, particularly for more than one person, consistently favours larger space.

5. Empirical Benchmarks from Constrained Housing Environments

The case studies in Section 4 reveal consistent thresholds at which spatial constraint begins to undermine occupancy duration, satisfaction, and housing stability. This section synthesises those patterns into an empirical typology. Drawing on formal and informal housing models, it identifies the floor area per person typically associated with sustained residence. Relationships are organised along two axes: internal space per occupant and typical length of stay. Together they outline a spatial envelope inside which compact housing continues to function without elevated turnover, dissatisfaction, or forced mobility.

Figure 1 plots each housing type by modal floor area per person and expected occupancy duration. Icons indicate typical household size and whether private kitchen and bathroom facilities are present. The horizontal axis measures duration in days (capped at three years) and the vertical axis shows floor area per person (capped at forty square metres to keep the focus on constrained dwellings). A dashed line marks a notional lower bound for long-term viability, derived from tenancy and satisfaction data.

Graph illustrating typical floor area per occupant (in square meters) versus typical duration of living period (in days) across various housing types. The graph highlights critical thresholds for long-term viability in compact housing contexts, with annotations indicating various types of accommodations.

Figure 1. Typical floor area per occupant and typical duration of residence across a range of constrained housing types. Points are annotated with the number of typical occupants and indicate whether private bathrooms and kitchens are included. The dashed line represents an approximate lower bound for residential use. Approximate modal values shown. (Graphic by author.).

At the lower end of the envelope sit dwelling types intended for very short stays or institutional use. Cruise cabins, emergency shelters, and São Paulo’s ten to fifteen square metre mini apartments fall here; these private, self-contained units support average stays shorter than one year [112]. Military barracks and student dormitories also appear in this zone. In the United States, unaccompanied military housing offers roughly thirteen to seventeen square metres per person in shared rooms, while standard dormitories provide about nine to eleven square metres per person, with longer stays enabled by institutional context and communal support systems.

A second cluster contains micro-units and efficiency apartments that offer more autonomy but remain tightly constrained. Tokyo’s one-room mansions and Hong Kong’s nano flats provide roughly fifteen to twenty-five square metres per person. Although popular with single professionals and students, tenancy data show average stays under three years and high turnover when more than one person shares these units [5,106]. New York’s adAPT pilot studios, twenty-four to thirty square metres, achieved moderate early satisfaction but saw notable attrition after eighteen months, particularly among residents working from home [107]. London co-living schemes display similar patterns, with average stays of eight to fourteen months [108].

The upper band of the envelope includes units that support longer residence and higher satisfaction. Mumbai’s eighteen to twenty-five square metre nano homes work for singles but show marked dissatisfaction among couples [111]. Government-built studio flats of thirty-five square metres in Singapore report satisfaction above ninety per cent, yet the main reason households give for planning to move is the wish for more personal space [109]. National market polling shows that thirty-six per cent of prospective buyers of private shoebox apartments cite lack of space as their chief concern, versus seventeen per cent among those considering units larger than forty-five square metres [110]. In Hong Kong, surveys find that sixty per cent of residents in units below twenty-five square metres rate their living space as unsatisfactory and that stress rises sharply when more than one person shares such flats [45,46,105].

A non-linear relationship emerges between space and duration. Dwellings smaller than fifteen square metres per person serve mainly short-term or institutional purposes. Between fifteen and twenty-five square metres, transitional use becomes feasible for single adults, but turnover remains high. From twenty-five to thirty-five square metres per person, long-term residence becomes more common, especially in self-contained units with daylight and acoustic buffering. Spatial efficiency offers some advantage for couples who can share kitchens and bathrooms, yet satisfaction improves markedly only when unit size nears forty-five square metres [105,109]. Tenancy duration rises by roughly one year for every additional ten square metres between fifteen and forty square metres [5,106].

Across locations and cultures, two functional lower bounds recur. Single adults can usually sustain long-term residence once a dwelling reaches about thirty square metres. Two-person households require roughly forty-five square metres to maintain privacy, reduce spatial stress, and limit turnover. Units below these limits repeatedly exhibit dissatisfaction, early mobility, and weak demand.

These empirical patterns reinforce earlier behavioural and regulatory thresholds. Units smaller than thirty square metres for single occupants and forty-five square metres for couples align with research showing that crowding below fifteen to twenty square metres per person elevates stress and social conflict [3,38]. While some households accept tighter quarters for cost, location, or life-stage reasons, the convergence of tenancy data, satisfaction surveys, and market behaviour around these thresholds supports their use as performance benchmarks. Compact dwellings smaller than those limits may meet short-term needs but seldom function as stable, long-term homes.

6. Synthesis of Evidence for Minimum Viable Floor Areas

The evidence presented across behavioural research, regulatory practice, and real-world market behaviour converges on a narrow and consistent range of floor areas required to support sustained residential use. Each of these domains identifies spatial thresholds below which occupancy becomes difficult to maintain, domestic activities begin to conflict, or turnover increases. When viewed together, these sources provide a triangulated basis for defining the lower bounds of functional housing.

Table 3 summarises this convergence. The first column lists internal floor area minimums found in regulatory frameworks across jurisdictions. The second column captures the size ranges of dwellings in widespread use within space-constrained housing markets, even when these units are considered suboptimal. The third column identifies the observed thresholds for sustained occupancy, based on tenancy duration, satisfaction, and post-occupancy outcomes. The final column presents a proposed technical minimum for each household type, grounded in the alignment of behavioural evidence, policy standards, and built examples.

Table 3. Summary of recommended minimum viable internal floor area.

Household TypeRegulatory RangeMinimums in Space-Constrained MarketsObserved Thresholds
for Sustained Occupancy
Proposed
Minimum
Single Person12–40 m215–25 m225–30 m230 m2
Couple30–55 m235–45 m240–45 m245 m2
Family
(3–4 people)
40–90 m245–75 m255–75 m260 m2

For single-person households, long-term viability consistently begins between 25 and 30 square metres. Units smaller than this are frequently tolerated, but studies report elevated stress, social withdrawal, or desire to exit within one to two years. Couples require 40 to 45 square metres to preserve privacy, functional differentiation, and behavioural autonomy. For three- to four-person households, the spatial demands of sleeping, socialising, working, and circulation require a minimum of 55 to 75 square metres depending on household composition and activities.

The proposed technical minimums are set at 30, 45, and 60 square metres for one-, two-, and three- to four-person households, respectively. These values represent the smallest viable floor areas capable of supporting long-term occupancy under compact housing conditions. They are not aspirational design targets or quality-of-life ideals. Rather, they define the floor below which spatial sufficiency begins to break down, even in well-designed, well-located dwellings. At these sizes, households can sleep, cook, bathe, work, and relax without constant compromise or persistent conflict. Below these thresholds, housing may still function temporarily, but is unlikely to support autonomy, stability, or psychological well-being over time.

While the difference between a three- and four-person household is meaningful, the 60 square metre value is proposed as a rounded baseline for both. A household of three may find this space sufficient; four people may require closer to 65 or 70 square metres. However, the use of round values in 15 square metre increments—30, 45, and 60—serves two practical purposes. It supports modular construction and housing aggregation, and it provides clarity and memorability for implementation in policy, planning, and code enforcement.

These thresholds offer a defensible reference point for performance-based housing standards. They reflect a lower bound on viability rather than a cap on quality or aspiration. While adaptation and local variation will always apply, this framework allows for compact housing solutions that preserve essential functions without compromising long-term habitability.

Example Floor Plans

Poor design can render even a large home unliveable. The challenge of maximising the liveability of a given floor area remains for talented designers and the marketplace. While this study does not prescribe specific design solutions, it is useful to demonstrate that the proposed minimum floor areas can accommodate full domestic function. Figure 2 presents one example of how units at 30, 45, and 60 square metres can be laid out to support daily life, based on a common and efficient multi-family configuration. The plans assume a double-loaded central corridor, with units arranged on a 4 m structural grid. Each dwelling has one exterior wall for daylight and ventilation. This configuration is compact, repeatable, and adaptable across many housing typologies.

Floor plans showing the layout of residential units of 30 m², 45 m², and 60 m², illustrating spatial dimensions for living, kitchen, and bathroom areas.

Figure 2. Feasible floor plans for one-person, two-person, and three- to four-person minimum floor area units. (Note that for the 60 sqm unit shown here, a second exit door, fire sprinklers, and/or mechanical ventilation would likely be required for code compliance in most jurisdictions.).

The 60 square metre unit essentially doubles the core layout of the 30 square metre unit, while the 45 square metre version adds a “half module” to provide a second sleeping area or more generous shared space. All three units use the same bathroom configuration, with the 60 square metre plan including two bathrooms. Each plan includes a dedicated space for a stacked clothes washer and dryer, and all units provide sufficient room for sleeping, eating, working, and relaxation. In the smallest unit, additional flexibility may be achieved through use of a lofted bed above a desk or integrated storage elements. The dimensions are comparable to those of an economy hotel room, a typology that has long demonstrated the spatial efficiency achievable within a minimal footprint.

These plans are not intended as optimal layouts, but rather as proof that the minimum floor areas proposed in this study can support essential domestic functions with clarity and coherence. Other configurations may yield better outcomes depending on site constraints, user needs, and architectural strategy. The key point is that at these floor areas, it is possible to provide private, enclosed spaces for sleeping and hygiene, areas for cooking and eating, and sufficient volume for work and relaxation.

7. Concluding Remarks

This study has identified lower bounds for internal floor area that appear necessary to support sustained residential use across three common household types. For single-person households, 30 square metres enables full domestic function with minimal spatial stress. For couples, 45 square metres allows for behavioural autonomy and reduced conflict. For families of three to four people, 60 square metres supports differentiated sleep, hygiene, and work zones while maintaining circulation and privacy. These values are not optimal targets, but rather performance-based thresholds derived from the convergence of behavioural research, policy standards, and market outcomes.

The goal of this work is not to dictate housing typologies or enforce rigid formulas. Instead, it is to clarify the spatial boundaries within which compact dwellings can function reliably over time. Below these thresholds, evidence from diverse settings points to higher turnover, reduced satisfaction, and compromised domestic activities. The thresholds represent a floor that supports liveable outcomes under spatial constraint, not a ceiling on aspiration or quality.

Clarifying this floor opens the door to more precise answers to larger systemic questions. What is the lowest feasible cost for delivering liveable housing at scale? How much residential floor area is required to support a given urban population within environmental constraints? What unit sizes are most compatible with modular or prefabricated construction? How can compact homes accommodate the needs of ageing populations, single-person households, or remote workers without compromising well-being? These questions cannot be addressed meaningfully without a clear understanding of how much space is minimally required to support daily life.

The thresholds proposed here do not resolve these challenges, but they provide a starting point. They define a stable platform on which designers, developers, and policymakers can build compact housing that is not just efficient, but functional and enduring. Future research should explore how these benchmarks intersect with environmental performance, construction systems, and regional context.

The risk of ignoring these limits is not just technical, but human. Compact housing that falls below the point of viability may be cheaper or more abundant in the short term, but it is less likely to support autonomy, stability, or well-being in the long run. In that sense, understanding spatial adequacy is not a matter of regulation alone. It is also a matter of practical foresight for cities, for builders, and for the people who will live in these spaces.

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Understanding Customer Needs (Diamond 2)

Let’s say I want to create a better eat-at-home meal solution for work-from-home professionals. That’s not really a strikingly novel problem. Indeed, food and beverage services are some of the oldest businesses in existence. I will face fierce competition to do the job. Why will customers choose my solution and not those of my competitors? 

Maybe because I do a better job of advertising, or because my product is more available, or because it’s priced lower. Those things are important for sure. But, much more significant, customers will choose my product if it better meets their needs.

The second diamond in the triple-diamond design process begins with a job to be done, understands the customer needs, and identifies one or more insights. There are two key goals of the second diamond. The first is to comprehensively catalog your customers’ needs. The second is to identify one or two latent needs – needs that are important but not yet addressed in the marketplace. We call these latent needs insights and they are useful in pulling a compelling solution concept when we get to the third diamond.

What are Customer Needs?

We aren’t here only talking about fundamental human needs in the sense of food, shelter, and belonging. Rather, for any given job to be done, customers typically care about 30 to 50 distinct attributes of a potential solution that if provided will result in greater satisfaction. We call these attributes needs, and they tend to vary a lot across individuals. For example, consider these two products. First, the Wendy’s Pretzel Bacon Pub Triple Cheeseburger. Second, the Soylent liquid meal. Both are solutions to the job “How might we provide lunch to hungry workers?” But, clearly the burger is better at meeting the primal craving for fat and salt, and the Soylent is better at meeting the need for high efficiency.

Wendy’s Pretzel Bacon Pub Triple Cheeseburger (Source: Wendy’s)
Soylent read-to-drink meal (Source: Soylent)

You have a focal customer, or type of customer, sometimes called your beachhead market, and represented by your customer persona. Once you have specified the target segments, a goal of the second diamond is to create a comprehensive list of user needs. There are entire textbooks that teach the methods for understanding user needs. In fact, I am a co-author of one of them (Ulrich et al. 2020). Here is an example of a comprehensive list of customer needs for a music player.

Example comprehensive list of customer needs for a music player.

How to Identify Customer Needs

In sum, you create this list by doing a set of open-ended interviews with individual potential customers. You interpret what you hear and see in terms of the individual underlying needs. 

You do your best to express these needs independently of solution concepts. So, instead of stating that the music player has a touch screen enabling a finger to rearrange the order of a playlist, you state that the music player allows the user to predetermine a sequence of songs, a statement independent of any particular solution concept. 

Once you have a comprehensive set of unique needs, you arrange them into clusters. For example, the primary need “The music player lets me control the music” is supported by a cluster of secondary needs that are more specific and detailed like “The music player lets me easily find and play music I have enjoyed previously” and “The music player lets me reduce frequency of play of a song.”

The full needs list is important for the ultimate product design. After all, you don’t want to miss anything important. You may also at some point use more formal quantitative customer research tools in order to understand which needs are most important across different market segments and the relative importance of say price and convenience for a particular segment. But, in the triple diamond model of design, our goal is the development of a compelling solution concept, and for that purpose, we are doing an initial exploration of customer needs in order to understand the important unmet needs among our potential customers – what we call an insight.

What is an Insight?

A woman named Emily Harper recently posted a video on the social media site TikTok showing how she prepares ground beef for use in recipes. With the comment that all this fat is disgusting, she is shown first cooking the meat and then washing it thoroughly with hot water using a wire strainer. The video went viral with seemingly half the world aghast that she had removed all the flavor from her food, and the other half thrilled at this revelation of a new technique for healthy living.

Your job as a zero-to-one product leader is not to pass judgment on crazy customer behavior. Rather, you benefit from acting like an anthropologist and asking yourself what deep insight does this behavior reveal about the nature of your potential customers.

In thinking about the opportunity for 99 Bowls, a service providing immediately available yummy food for work-from-home professionals, I hope to observe Emily with a curious and open mind.

The insight I derive from watching Emily going to extreme lengths to adhere to strict dietary constraints is that some individuals feel a compelling need to tightly control the macro nutrient profile of the food they eat.

Among designers, the term insight refers to a user need that is:

  1. authentic
  2. non-obvious, and
  3. significant.

Authentic means that the insight is based on an actual observation of users in the target market.

Non-obvious is self explanatory.

Significant means that if your solution addresses the need it would result in a meaningful enhancement in the value perceived by the customer.

In the second diamond of the triple-diamond model the designer achieves two goals: first, comprehensively identify the customer needs in the target segment and second, flag a small subset of those needs that comprise insights. 

Four Categories of Needs

The result of a set of customer needs interviews is a comprehensive list of customer needs, usually 30-50 distinct items. These needs can be sorted into four categories, illustrated by a framework from the Japanese total quality movement of the 1980s and 1990s called a Kano Diagram.

Four categories of needs as represented by a Kano Diagram. (Adapted from original by KTU.)

The horizontal axis is the extent to which the need is satisfied by the solution. The vertical axis is the resulting change in customer satisfaction, or perceived value of the solution.

The “don’t care” needs are needs that are irrelevant to the customer. Address them or not –  the customer’s satisfaction does not change. For example, for me, whether or not the food you deliver to me is gluten free, I don’t notice or care.

The “linear” needs are those for which the customer’s satisfaction is essentially directly proportional to the extent to which your solution addresses the need. For example, affordability is often a linear need. When the food is a little more expensive, I’m a little less satisfied.

The “must haves” are needs that if fully addressed do not result in dramatic improvements in satisfaction, but if not addressed at all, result in extreme dissatisfaction. For example, if a food container is microwavable, I don’t particularly notice. However, if the container immediately melts or sparks in the microwave, I’ll be very dissatisfied.

The “latent” needs are needs that if unaddressed are not missed, but if addressed result in surprise and delight. For example, if my food service allows me to precisely specify the macronutrients of my lunch, say 20% carbohydrates, 40% fat, and 40% protein, I’m thrilled.

While there have been some attempts to use the Kano framework quantitatively based on survey methods, it’s mostly conceptual. It gives you a way to think about customer needs and to direct your investment. Ignore the don’t cares. Deliver the must-haves. Invest at competitive parity in the linear needs. But, then, seek out the latent needs like hidden gems. The latent needs are by definition non-obvious. To the extent that they derive from your observation of users, they are authentic. Those that are significant – a big deal for customers if addressed – are insights. These insights will be used in the third diamond to pull compelling solution concepts.

How to do Customer Interviews

OK, but how do I actually get the information to identify the customer needs. Put simply, you get out of the office and interact with customers.

More specifically, you conduct at least 10 one-on-one interviews for each distinct market segment. For new zero-to-one products you’ll probably just have one beachhead market. Perhaps surprisingly, you need just 10 interviews to identify 90 percent of the customer needs that would eventually be revealed by interviewing hundreds of customers.

I recommend you do these interviews as follows:

  • Identify about 10 potential customers for each segment. These customers need not be typical. In fact, they could be extreme in some ways. After all, our ultimate goal is to find unmet needs, and sometimes the extreme users are better at revealing those needs. For example, if our segment is work-from-home professionals, we might interview some professionals who work from highly remote locations, say a cabin in the mountains. Or, we might interview workers who are extremely passionate about food, so called foodies, say those who are food writers. Or possibly those with extreme food regimens, say adherents of ketogenic diets.
  • Conduct the interviews either alone or with one other person. You can get by doing them alone, but you’ll find it easier to keep track of what you learn if you have a partner. The other advantage of doing interviews in pairs is that you can engage a lot of people in the process. For example, bringing members of your technical team on interviews is a very powerful way of developing empathy for the customer.
  • You can use an audio recording device, but honestly I rarely do. I think notes are pretty much just as effective. I think recordings are a bit obtrusive and they are rarely actually transcribed and used. Having said that, I do take a lot of photos and even some short video clips, as the visuals are very helpful in reporting on the interviews and in remembering specifics.
  • Do the interviews in the customer’s use environment if possible. If interviewing office workers about lunch, do the interview around lunch time at their offices. The reason for this approach is that you are going to observe as much as you are going to listen. You will develop an entirely different and better understanding of your customer if you observe them in their own world.
  • Plan on about an hour of unstructured conversation. I know this is a bit daunting for many people, but I’m pretty sure you can do it. I have four questions that I use to get the conversation started, but rarely need them. You simply start with an open-ended question related to the job to be done. For instance, “what’s your plan for lunch today?” Once you’ve asked a question, listen carefully to the response and look for an open door. For example, your customer might say, “well, I usually skip lunch.” That’s a huge open door. You know what to do – step through the door by asking, “really? Why’s that?” I guarantee a big fat customer need is about to be delivered to you with that question. The response might be “i’m trying to lose a few pounds” or “I don’t have time” or “I’m planning to eat a big dinner later” or “I forgot to bring my food” – whatever the customer says, you’ll learn a lot. If you walk through a bunch of doors and find yourself way off topic, bring the conversation back to the job to be done with one of your prepared questions. The prepared questions I like are “How do you currently do the job” which you’ll ask more naturally like “what do you do most days for lunch?” or “What issues do you consider when choosing what to do for lunch” or “what most annoys you about lunchtime?” or “what would be your perfect lunch experience?” Any of these questions will result in more open doors – then you step through them.
  • Whenever possible, ask the customer to show you as opposed to tell you about the question. For example, if the customer responds “I bring my lunch” ask to see the lunch itself. You’re going to learn a lot by observing them. For example, you might learn about office food storage, or dietary preferences, or portion sizes, all revealing of needs in a more direct and truthful way than would be an oral response to a question.
  • After your interview, sit with your partner and debrief. Revisit the conversation and identify as many needs as you can, even if obvious or obscure. This process results in a long list — usually 30-50 distinct needs. I say usually, but for some complex products there could be many more. I once worked on a project to design a better blood pressure monitor, and we identified about 400 distinct customer needs.
  • Finally, work to identify those needs that could be considered insights.

What About Large-Scale and Quantitative Market Research Techniques?

The triple diamond model of design is highly effective in understanding latent customer needs and in developing novel solution concepts in response to those needs. However, it has no mathematical underpinnings. There is no notion of statistical significance or estimation of the magnitude of a consumer response to a given feature. Many of you probably have backgrounds in engineering, economics, or mathematics and may be uncomfortable relying on such a qualitative process to create new products.

Of course your discomfort is justified. After all, in business we do really need to answer questions like how big is the addressable market? What should our price point and product specifications be? How will our new product fare in a competitive landscape?

These and other important questions are best answered with quantitative market research tools. 

But be careful – the triple-diamond model is intended to engage you in a rich and multi-sensory way with the customer. You won’t achieve that goal with a web-based survey. Avoid the impulse to employ quantitative market research techniques until after you have used the customer-centered, qualitative approach captured by the triple diamond model.

Notes

Ulrich, Eppinger, and Yang. 2020. Product Design and Development. McGraw-Hill.

List of highest-calorie fast-food burgers available in the United States. https://www.eatthis.com/fast-food-burgers-highest-calories/

Wikipedia description of Kano Model. https://en.wikipedia.org/wiki/Kano_model

The Triple-Diamond Model of Design

I’ve been a product designer my entire adult life. Here is one of the products I created, the Belle-V ice cream scoop. In full disclosure, I had a lot of help from a talented team. When people see the product they impute genius to the designer – wow, that’s amazing. How did you come up with that?

I’m using an example of a physical good for specificity, but I’ve experienced the same kind of reaction to digital products and services.

The reality is that I learned an effective process when I was in my 20s and I’ve applied that process repeatedly, sometimes weekly or even daily for 40 years. When you only observe the outcome, the results seem magical. But, the truth is that a fairly straightforward sequence of process steps can reliably lead you to a great result.

Design is just another word for the pull approach to innovation. All design processes are a sequence of steps that begin with some articulation of the “what” and result in some description of the “how” – the process moves from what to how.

Commercial phase-gate product development processes are just an elaboration of that basic idea, with lots of detail. My textbook on product design and development (Ulrich et al. 2020) is a comprehensive description of that detail. Most of you working in larger organizations probably use some sort of phase-gate process that is specific to your industry.

But, here I’m going to abstract a bit, and focus on the elemental design process – what is design at its very core. While design is the core problem solving approach within the product development process, design can be applied beyond product development. It’s almost a building block of being human – of dealing with life.

My goal is to describe the design process in a way that it can be used in myriad situations, from the creation of a new product from scratch, to the improvement of an existing product, and even for solving internal innovation challenges such as finding new ways to reduce waiting times in emergency departments.

To reiterate, the standard phase-gate product development process is a fully elaborated methodology that typically includes the roles of different functions within the organization. It emphasizes not only what to do in each phase, but the notion of a gate that must be cleared in order to proceed to the next phase. I am now going to boil that basic process down to its essence to give you a tool I call the triple-diamond model that can be used not just in zero-to-one product development, but also in almost any other problem solving situation.

To give credit where credit is due, the triple-diamond model is my extension and elaboration of the Double Diamond Model articulated by the UK-based Design Council, a non-profit organization with the mission of improving design practices.

The three diamonds correspond to three steps. 

  1. Clarify the job to be done in a jobs analysis
  2. Understand the needs of the customer or user. 
  3. Create a great solution concept.

In practice, a fourth phase is usually important – implementing that concept in a way that the organization can actually deliver the solution. This involves writing the code, designing the parts, and planning for production.

The three diamonds each represent a cycle of divergent and convergent thinking. For each diamond, the designer explores alternatives, and then focuses.

The first diamond answers the question, “What is the job to be done?” It starts with a target customer and the gap or pain point as you have first sensed it, and it results in a carefully considered reframing of the design problem in terms of a job to be done. In fact, one of the critical elements of an effective design process is not even really problem solving so much as problem definition.

The second diamond begins with a job to be done and develops a comprehensive understanding of the customer needs, which are those aspects of a solution that could result in satisfaction and even delight if satisfied. The convergent portion of the second diamond identifies one or a few insights, which are essentially important customer needs that were previously not known.

The third diamond uses those customer insights to pull many possible solution concepts and then selects one or a few for further refinement and testing.

Let me show you how the three diamonds played out for the Belle-V scoop. I started with a vague sense that ice cream was really hard to scoop. In diamond 1, I focused on the at-home consumer of ice cream and came up with the job to be done “How might we better dispense bulk ice cream into individual portions?” In the second diamond, I observed people scooping ice cream and noticed that the wrist angle was quite awkward, even painful for some people. That insight allowed me to pull several different solution concepts, including the one that eventually was embodied in the product, a more or less conventional scoop, but with the scoop angled relative to the handle.

Of course, really, it’s diamonds all the way down. The triple diamond model focuses on the concept development process, but when the team proceeds to build the product based around a concept, it will almost certainly use additional cycles of divergent and convergent techniques in order to solve downstream problems, say for establishing a product architecture, or implementing specific components of the solution. For example, even after we had converged on the solution concept of an angled scoop, we did a huge amount of exploration to find the final form of the object. Another diamond focused on the detailed design of the shape of the scoop and handle. And for that matter, there was another diamond when we considered the surface finish of the scoop – divergent exploration of alternatives and then convergence on tri-valent chrome plating.

Some of you are thinking that this model seems pretty tidy for a very simple piece of hardware like an ice cream scoop, but may not apply to more complex goods and services, say to enterprise software or to a hotel experience. I have a couple of reactions to those reasonable thoughts. 

First, as an aside, there’s a reason they call it HARD-ware – it’s hard. Even a simple object like an ice cream scoop presents a lot of complexity and challenges when it comes to actually getting it to the marketplace. 

But, more substantively, for new, zero-to-one systems, software, or services, you must still devise an overarching solution concept. For example, consider LinkedIn – the top-level solution is essentially a user-created resume-like profile with the ability to establish a connection between two individuals, and then the ability to search 1st, 2nd, and 3rd order connections in the resulting professional network. Such an overarching concept could be developed with the triple diamond model. 

For established systems, the triple diamond will be unlikely to be applied to the entire product or suite of products, but rather more likely to a feature within that more complex product. For example, once LinkedIn had become a successful product, the triple diamond model could still be applied, but to a new feature, say the creation of the follower feature, which allows individuals to follow another person and get updates that person publishes, but without requiring the individual to become a bi-lateral connection.

Problem Solving, Design, and Design Thinking

I happened to be on a holiday ski trip when I was writing this chapter. (I know, that doesn’t sound like that much of a holiday.) I kept thinking to myself, skiing is fun, but it’s a huge annoyance to actually get on the slopes. For most novice skiers, you have to procure skis, boots, poles, helmet, goggles, and warm clothing. Then, you have to put all that stuff on. Then, while fully dressed in really warm gear you have to walk awkwardly from transportation to a ski lift, sometimes navigating a flight of stairs. Then, you put on the skis. By then you are sweating and your goggles are fogged up. Next you wait in a line. Then you get on a windy and cold ski lift and become quite chilled. When you finally get to the top of the mountain, you stare at a map trying to figure out the best route down. Finally, you get to slide on the snow, which is actually quite fun. I’m an incurable innovator and so I found myself posing the question, “How might we improve the experience of getting skiers onto the slopes?”

If I were a trendy corporate consultant, I would call this a “design thinking” problem. But, I’m actually a bit of a crusty old designer. I’ve taught design for more than 30 years. So, I have to ask “what exactly is design thinking” and how is it any different from plain old design?

Well, first let’s first go back to the definition of innovation and design.

I define innovation as a new match between a solution and a need. Innovation can result from a push – starting with the solution and looking for a need. For example, what might we use the blockchain for? Or, it could start with the need and pull the solution, like I framed the skiing challenge. “How might we improve the skier experience?” Design is innovation anytime you are pulling a solution from a need.

So considering our definition, the short answer to what is design thinking is that it is design. Really. You apply the same process to creating a better ski experience as you do to creating a better ice cream scoop, or a better fitness app. In fact, the word design thinking annoys a lot of designers, because they are usually less interested in thinking about problems than in actually solving them. 

Once I cool off a bit about the weird term “design thinking,” I realize there may be a gem of an idea in there, and that a bit of nuance may in fact be warranted.

A useful definition of design thinking might be that it is design of things we don’t normally think of as designed.

For example, here are some problems for which the design process could be used, resulting in solutions that would not normally be thought of as designed artifacts.

  • How might we improve the patient experience in the emergency department at our hospital?
  • How might we improve the convenience of using a bicycle for transportation?
  • How might we create a delightful food delivery service?

A lot of people talk about needing to apply more design thinking in business. I find myself wondering if the desire for design thinking is really just a reaction to the use of too many spreadsheets and PowerPoint presentations, disconnected from customers and from exploration of solution concepts. This reaction reflects a desire for a different and better culture of innovation.

I do think that good designers exhibit a few desirable elements of culture. Interestingly, most of these elements don’t need to really be confined to design. Here are five:

  1. Designers exhibit a bias for action.
  2. Designers tend to be optimists, exhibiting a culture of yes.
  3. Designers tend to use exploratory prototypes early in the problem solving process.
  4. Designers tend to be skilled at visual expression.
  5. Designers tend to use empathic methods for understanding customers.

Despite my enthusiasm for all things design, I won’t argue it is universally the best approach to problem solving. For example, it would be a mistake to abandon elements of Six Sigma, Total Quality Management, the Toyota Production System, and data-based approaches. It would also be a bad idea to use a design process to find the volume of a geometric shape, a task better suited to an algorithm.

But, for a huge set of challenging problems, design is a great approach. It is fundamentally divergent and open-ended in its perspective on addressing user needs, and that’s useful whether you are designing a bridge, enterprise software, or an insurance claims process.

Notes

Karl T. Ulrich, Steven E. Eppinger, and Maria C. Yang. 2020. Product Design and Development. McGraw-Hill. New York.

Double Diamond Model. UK Design Council.
https://www.designcouncil.org.uk/our-work/skills-learning/tools-frameworks/framework-for-innovation-design-councils-evolved-double-diamond/