This post adds extra information to part of an earlier post “Severely Constrained Design”.

The Scottish Special Housing Association (SSHA) and the Edinburgh University Architectural Research Unit (ARU) developed a Computer Aided Design program, called House Design. (Bijl et al., 1971) Whilst working at Edinburgh University and SSHA, I was partly responsible for the practical implementation of this program particularly simplifying the interactive positioning of components.

House Design allowed experienced designers to interactively design house types within Circular 36/69 restraints, which had already been incorporated, with some minor variations, into the Scottish Building Regulations.

All location, component and assembly drawings and bills of quantities were then automatically produced without further interaction, by reference to a complete set of standard component and assembly details. That is all possible component and assembly details had been identified, detailed and quantified in advance of their being required.

External walls, windows and external doors were located by placing pairs of 300mm square symbols constrained to be within a 300 mm grid. Structural partitions, non-loadbearing partitions and internal doors were located by placing pairs of 100mm square symbols constrained to be within a 100mm sub-grid. External walls, windows and external doors were therefore notionally 300mm wide whilst structural partitions, non-loadbearing partitions and internal doors were notionally 100mm wide.

Grid Based Component Location

Extra information such as window height or door swing direction was supplied by pulldown menus or extra pointing. At the time this was described as being a 2½D model; most information being derived from the 2D plan with some default height information and a little extra input to supply information about the 3rd dimension.

House Design Dimensional Constraints

Of particular importance was the adoption of a standard 2600mm floor to floor height. This allowed stair symbols and floor openings to be accurately known. Thus far, this all conformed to Design Bulletin 16: Dimensional Coordination in Housing (MoHLG, 1969). Problems arose though when actual component widths differed from their 300 or 100mm notional widths.

Symmetrically Located Components

Without finishes, external walls were actually 240mm wide rather than 300mm, structural partitions 74mm wide rather than 100mm and non-loadbearing partitions 50mm wide rather than 100mm. Design Bulletin 16 recommended (probably required) that internal components were located with their finished faces on a 100mm grid line. Somewhat surprisingly it was thought that this would aid the location of components on site, perhaps assuming that they would all be pre-finished and in modular lengths.

Locating components symmetrically within their grid space with 30, 13 and 25mm offsets as illustrated above, meant that location plans could be automatically dimensioned, with dimensions to the structural face of the components, that is before plasterboard etc. was fixed and exactly as site operatives found them. This meant that as shown below grids could be ignored on site and not shown on location drawings; their work having been done in organising the system, they were no longer needed and could be discarded.

House Design: Accurately Dimensioned Plan

The use of 300 and 100mm grids did however usefully reduce the number of component sizes especially for windows, external doors (300mm increments) and internal doors (100mm increments). This was at the expense of non-modular partition lengths, which in any case were less likely to be manufactured off site.