In 2015, the UK government published the Nationally Described Space Standard (NDSS) following a housing standards review. Unlike its predecessor, the Housing Quality Indicators, the NDSS is not a requirement to receive government subsidies. The introduction of the NDSS has coincided with a significant shift in affordable housing supply with most housing developments currently being built without government subsidies. The following discusses the impact of these changes on the sizes of recently completed affordable housing.

Space standards prescribe minimum dwelling and room sizes based on the spaces deemed necessary for typical domestic activities. The minimum floor areas and dimensions largely derive from anthropometric measurements, standard furniture dimensions, activity zones associated with the use of furniture and daily activities, and general circulation areas as well as the space needed for access. [1] They are widely seen by regulators and the housing sector as a reliable measure of dwellings being usable and fit for their intended purpose. Dwelling size not only determines usability but also has a significant long-term impact on the diversity, flexibility, and adaptability of housing, and small dwellings in particular can have a negative effect on the health and well-being of occupants.

In England, space standards have historically been implemented as a condition for receiving housing subsidies. Most recently, the Housing Corporation introduced Housing Quality Indicators as a funding requirement for its 2008–2011 and 2011–2015 Affordable Housing Programmes. However, in 2015, the use of space standards as a subsidy condition has ended with the introduction of the current Nationally Described Space Standard, which was introduced as a planning tool. [2]

As the current standards are implemented through local plans, the decision to adopt the NDSS remains at the discretion of local authorities. The local authorities wishing to adopt the NDSS must provide an assessment of the need for and economic viability of incorporating the NDSS. This is done in order to prevent increased standards from creating additional construction and land costs that are unsustainable in the local housing market, impacting housing affordability. Moreover, the adoption of the NDSS does not guarantee the full compliance of new affordable housing units, as they are negotiable. Developers often negotiate planning requirements and compliance with space standards, particularly if site constraints or local housing market conditions would render their developments financially unviable. 

As there was no available data, we submitted environmental information requests to all 322 local planning authorities in England. We sought information on when they adopted the NDSS into their local plans or supplementary planning document, or whether they are planning to do so. We also asked whether they use alternative standards in assessing planning applications. 

Of all contacted local authorities, 79% (n=253) responded: 37% of them (n=93) had adopted the NDSS in their local plans and policies, and a further 8% (n=21) adopted them as a design guidance in the form of a Supplementary Planning Document (SPD). The number of local authorities who adopted and are planning to adopt the NDSS are shown per year in the graph below. Of the local authorities that did not adopt the NDSS, 85% (n=112) reported that they used no other space standard in their local plan or planning guidance.

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Figure 1. The number of local planning authorities who adopted the Nationally Described Space Standard.

Our dataset is accessible at this link. 

The significant shift in how affordable housing design is controlled has coincided with a shift in affordable housing provision. New affordable housing in England is mainly funded and provided through three primary means: a) housing associations supported by subsidies from Homes England and the Greater London Authority, b) housing associations using their own income generated from activities in the private housing sector (cross-subsidies), and c) planning obligations imposed on new private developments. While most affordable housing in the past received state subsidies, the number of affordable housing units gained through planning obligations imposed on new private developments have exceeded the number of affordable housing units built using government subsidies. According to the National Planning Policy Framework (2019), in developments with more than 10 dwellings, generally at least 10% of units must be for affordable homeownership, which includes homes offered via shared ownership and equity loans.

A shift to supply by the private sector means that incentivising and controlling affordable housing and its design is more difficult, as it has become a by-product of speculative housing developments and is thus of secondary concern. Consequently, the design of affordable housing is influenced to a greater extent by the preferences of the private sector.

We studied the implementation of space standards in new affordable housing within the context of this voluntary and negotiable adherence to these standards. Our analysis is based on data derived from the planning applications of 153 new housing developments (9,876 affordable housing units) completed in 2021.

In our sample, the most common dwelling types were: 2B(ed)4P(erson) (23%) and 3B5P (19%) two-storey houses and 1B2P (16%), 2B3P (10%), and 2B4P (14%) flats. These five types made up 88% of all affordable housing in the analysed sample. For each common dwelling type, a very wide variation in dwelling size was observed (Figure 3). For instance, 2B4P flats ranged from 60.2 m² to 110.2 m². Despite this, the gross internal areas of units were tightly clustered around the median. 72% of 1B2P, 66% of 2B3P, and 65% of 2B4P flats, as well as 51% of 2B4P and 62% of 3B5P houses were within 5% of the median GIA (±2.5m² in a 1B2P flat to ±4m² in a 3B5P house). 

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Figure 2. Dwelling size distribution per dwelling type. The minimum dwelling size for flats is 50m² for 1B2P,  61m² for 2B3P, and 70m² for 2B4P in the NDSS.

Figure 3. 

Mean dwelling sizes changed between 6 m² (in 2B3P flats) to 22 m² (in 3B5P houses) across different regions (Table 6). They were consistently higher in London, the South East, and the South West and lowest in the East of England, East Midlands, West Midlands, and Yorkshire. Consequently, the compliance rates with the NDSS were highest in London (80%) and the South East (65%) and lowest in the East Midlands (8%) and West Midlands (13%). 

Our study found that 57% of new-built affordable housing meets the recommended space standards of the NDSS and 81% those in the HQIs. The most significant difference in compliance rates related to dwelling types (flats and houses). While flats had a high compliance rate with both standards (NDSS: 71%, HQI: 87%), houses only showed similar levels of compliance with the lower HQI standards (NDSS: 18%, HQI: 80%). 

In the studied sample, 95% of affordable housing units in London were flats, compared to only 30% of units outside London (cf. DLUHC, 2022b). As a result, 55% of flats in the sample were from London, where space standards comparable to the NDSS were already adopted in 2011 and applied to all tenures and developments in the metropolitan region. However, only 28% of local authorities nationally had adopted the NDSS. The higher compliance rates of flats, therefore, relates to the highest compliance rates in London (79% compared to an average of 31% in other regions). 

The differences in the compliance rates of dwelling types with the NDSS relate, only to a certain extent, to local plans. Even though the compliance rates were significantly higher in local authorities where the NDSS was adopted (p < 0.01), the differences in how flats and houses meet the standard were persistent. The overall compliance rate of flats was 74% in areas where the NDSS was adopted and 68% where it was not, compared to 47% and 13% for houses. These findings suggest that there are different industry standards for flats and houses, with the standard flat sizes more aligned with the NDSS and standard houses with the HQI. 

The strong correlation between dwelling types and standards are likely a result of how these standards are generated. The NDSS recommends higher overall dwelling sizes than those in the HQI, but the two standards do not differ significantly in their reasoning of space. Both standards are based on the furniture dimensions, activity zones, and circulation space required for maximum occupancy, which are nearly identical. 

While the NDSS was adapted from the London Housing Design Guide, which was written for London where the majority of new housing consists of flats, the HQIs were national and therefore had a greater concern for single-family houses. While the method for calculating overall dwelling sizes used in the LHDG is appropriate for flats (i.e. adding up minimum room sizes), terraced houses pose additional geometric problems. In terraced houses, the living room and kitchen are located on the ground-floor and bedrooms and bathrooms on the first-floor. Terraced housing design thus requires balancing room sizes and layout efficiency on identically shaped and sized ground- and first-floor levels. However, according to room-by-room calculations, the floor areas required for these spaces are not the same.

We also found that the HQI standards are preferred by private housebuilders in developments that predominantly consist of houses (thus outside London). Comparing private house types by different volume housebuilders, all had sizes close to the HQI standard. In addition, in many of the planning applications analysed, the HQI scores of affordable unit types were included on submitted plans, even though they are not required. The HQIs were used as a voluntary industry standard or a measure to demonstrate the usability of housing. This not only shows that some standards are habitually used in housing organisations, but that standards are used as a form of reassurance both at an organisational and regulatory level. Thus, the prolific use of standard types creates consistency in dwelling size across affordable housing, even when space standards are not mandatory. 

[1] For example, the London Housing Design Guide (Mayor of London, 2010) and Design Bulletin 6: Space in the Home (MHLG, 1963) detail how these standards are calculated based on furniture dimensions and typical activities at home.

[2] An exception to this was the inclusion of some minimum dimensions pertaining to the access and use of dwellings in the Building Regulations. The Approved Document M (2015), now incorporates minimum dimensions for circulation spaces, bathrooms, WCs, kitchens, and bedrooms according to three categories: M4(1) visitable (applicable to all dwellings), M4(2) accessible and adaptable, and M4(3) wheelchair user dwellings. 

NDSS was were no longer a funding condition by Homes England in the Affordable Homes Programme 2016–2021.Homes England’s Affordable Homes Programme 2021–2026 funding requires all units to meet at least 85% of the NDSS.