The metrication of Parker Morris Standards
In the UK, the process of metrication – the switch from imperial to metric units of measurement – was officially agreed in 1965. Yet, there is still a mix of imperial and metric measurement in use. Journey distances and travel speeds are measured in miles, but shorter distances in metres. Petrol is measured in litres but fuel efficiency in miles per gallon. Room dimensions are often shown in feet, although furniture is measured by centimetres and metres.
While many sectors were reluctant to change to a metric system, the building industry embraced the switch, as the UK was already developing international metric and decimal standards for engineering products with the International Standards Organisation (ISO). Since the 1960s, the British Standards Institution (BSI) had worked with the ISO to push for the adoption of the International System of Units (SI units). In 1968, the Metrication Board was created to coordinate the metrication programme (Fig. 1). And in January 1972, metric dimensions became official for all new building schemes: the metrication of industry had begun. That year, the floor-to-floor height of 2.60 m for new homes became mandatory. 
Figure 1: Posters by the Metrication Board (1970)
However, it would take several years to change not only the units of measurement but entire industries, and more importantly, ways of thinking and operating. As highlighted by the BSI in 1967, the change to the metric system in the construction industry ‘would not be meaningful unless it implied a change to metric thinking as opposed merely to the translation of present values into exact metric equivalents’.  The government believed that metrication would only be successful if local authorities adopted the metric system and used the new metric building components themselves, ‘otherwise the manufacturers will not be willing to produce or even design them’. They also recognised the need for some measure of compulsion, given ‘past experiences have shown that advice on the best use of preferred or standard dimensions is not in itself sufficient to ensure that authorities use standard components’. 
At that time, the standards used for new housing schemes were the so-called Parker Morris Standards based on the housing report Homes for Today and Tomorrow published in 1961 and written by the Parker Morris Committee for the Ministry of Housing and Local Government. One would assume that the metrication of these standards would just mean converting measurements from imperial to metric units, but in fact it entailed a long process. Several discussions took place on how best to convert the imperial measurements in the report to metric dimensions without sacrificing space and considering the needs of industry. The main challenge was that the Parker Morris Standards could only be rounded up, given that the mandatory floor areas were defined as minima. Therefore, metric dwellings would be slightly larger than their imperial counterparts. As Walter Ulrich, undersecretary of the Department of the Environment stated, ‘it would seem politically impossible to convert them to metric by rounding down’.  In the few cases were reductions were proposed, Ulrich further highlighted that these had to be compensated, ‘either in the main area of the dwellings or the storage space, but in all cases there is at least a countervailing increase in the other element, so that the minimum area for the dwelling as a whole will be more than at present in all cases except one, where it will be the same’. 
Figure 2: Recommendations for metric sizes of the Parker Morris Standards by the architect K.M. Wood to Mr. Walter Ulrich (1967). National Archives.
Figure 2 shows the edits pencilled in by Ulrich, who thought it was ‘politically impossible to reduce this minimum for living space and storage […] by more than at most one sq. ft. in any case’.  Measurements were rounded up to the next whole number, therefore, in the case of storage where area increments were smaller, 0.5 of a square metre was suggested.
The Parker Morris Standards led to the creation of several government-issued design bulletins that provided detailed information on issues such as housing layouts, furniture dimensions, and the standardisation of components and construction methods. In order to provide detailed guidance on how to use the newly adopted metric standard dimensions, the government published Space in the Home: Design Bulletin 6, metric edition (1968), which superseded Design Bulletin 8: Dimensions and Components for Housing (1963), which was based on imperial measurements. Design Bulletin 6 showed how the main activities in a home related to furniture and space requirements. It provided metric dimensions for the typical items of furniture for which the dwelling designer should allow space for, and provided anthropometric data about the space needed to use and move furniture about (Fig. 4). The bulletin also included typical room plans for a terraced house that would meet the requirements and provided the updated metric measurements for minimum floor areas (Fig. 5).
Figure 3: Ministry of Housing and Local Government, Design Bulletin 8: Dimensions and Components for Housing: With Special Reference to Industrialised Building (1963)
Figure 4: Ministry of Housing and Local Government, Design Bulletin 6: Space in the Home, Metric Edition (1968)
Figure 5: Recommended internal floor areas by the Parker Morris Committee in imperial units (left) and floor areas in Design Bulletin 6 in metric measurements (right). In green are the added and in red the subtracted square metres in the conversion from imperial to metric measurements.
Correspondence within the Ministry of Housing shows that some local authorities were treated as ‘special’ cases before the Design Bulletin 6 was issued and permitted to introduce the metric system early. Hoping that they would ‘be carrying out pilot schemes in metric, and something might be learnt from their experiences’, the central government considered giving subsidies to support experimental schemes.  In 1971, the cost of the average metric dwelling was estimated to be 1.25% higher than the imperial one (£38 more per unit). In a press release, J. A. Fowler pointed out that whilst costs have increased ‘there are savings to be made out of the greater standardisation which the change to metric will bring’. 
Another problem caused by the metrication that would affect how the Parker Morris Standards would be implemented, was a change in furniture sizes. Before the Design Bulletin 6 was published, discussions with the National Bedding Federation took place to revise bed sizes. They were proposing a single bed of 2 x 1 m and a double bed of 2 x 2 m. But John Noble, architect at the Department of the Environment, and Cleeve Barr, Chief Architect of the National Building Agency, were against the proposed widths. Instead, Noble believed that the increasing demand for 3 ft. single beds (91 cm) should become the planning norm for single bedrooms rather than the 2 ft. 6 in. small single beds (76 cm) previously popular. Noble argued that minimum bedroom sizes should be abandoned and replaced by standard bed sizes in order to avoid bedrooms that are too small to fully accommodate a standard bed (Fig. 6). He observed that ‘People are growing – we can’t stop them, and are already demanding more comfort in their beds as their living standards rise. Even if the rooms are small, at least the beds should be comfortable.’ 
In the discussions between the building industry and the government during the process of metrication, the Parker Morris Standards were considered as the permitted minimum. An analysis carried out by I. B. & Consortia Group and R & D Group (1968) reviewed 106 plan types designed using imperial measurements and compared them to the minimum floor areas in the Parker Morris Standards to test a 1.5% downward tolerance in overall floor area (Fig. 7).  They found that a high proportion of housing schemes were within 0.5% above or below. In flats, most schemes met the Parker Morris Standards’ minimum dwelling areas, and a substantial proportion was considerably above (40%). Houses were 50% below and 50% above the Parker Morris Standards, with 35% within the 1.5-1% and 27% within the 0.5% tolerance of total dwelling size. In order for schemes to comply with Parker Morris Standards, they suggested that it would be preferable that the downward tolerance in floor area be reduced to 0.5%. They also suggested how floor areas should be measured in relation to an established grid to ensure compliance with the required standards (Fig. 8).
Figure 6: Standard bed sizes in the Design Bulletin 6.
Figure 7: Findings from I.B. & Consortia Group on the tolerance in applying Parker Morris Standards in existing housing schemes.
Figure 8: Correspondence on how measurements could be calculated using the proposed grid lines
The switch to metrication slightly increased dwelling and storage areas set out by Parker Morris Standards, as can be seen in Figure 5. For example, a 6-person 2-storey terrace, semi-detached house, and maisonette are the dwelling types that increase in overall dwelling size the most, by 0.53 m2. In comparison, a 6-person flat increases only by 0.11 m2 in total floor area. Other overall dwelling areas such as a 2-person flat and single-storey house remain the same. Storage areas in a 4-6 person flat or maisonette increase approximately by 0.60 m2. In houses, however, storage space only increases 0.14 m2 for 4-6 person houses and 0.21 m2 in a 1-person house. Storage in a 3-person house decreases 0.18 m2 but increases in its overall dwelling size by 0.32 m2. The increase in floor areas is relatively small, however, the addition of half a metre of storage can make a significant difference to occupants.
Today, even though the construction industry uses the metric system, materials such as timber are still sold in both imperial and metric units. Elements such as plywood, blockboard and hardboard are sold in soft metric sizes, meaning they are exact conversions of their imperial units. The SI system is metric and all in base of 10, which makes it easier for calculations. When, for example, elements such as plywood are converted from imperial (in a base of 12) to metric units, a lack of precision and a margin of error are often accepted.
The metrication of the Parker Morris Standards shows that defining dimensional standards is a difficult task and consists to some extent of subjective decisions. As seen in Figure 5, standards were converted and rounded up to achieve simpler metric dimensions, rather than using exact imperial-to-metric conversions, raising questions about the specificity or flexibility of these dimensions in the first place. As seen in the minutes and correspondence between government officials, architects, and industry-related professionals, the standards are the product of negotiations.