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Prior to the end of WWII, the British Iron & Steel Federation worked closely with Architect Frederick Gibberd & Engineer Donovan Lee to develop several steel framed BISF prototype houses & flats that could be erected quickly and efficiently using very little skilled labour. However, despite the name B.I.S.F being synonymous with the eventual production dwellings, it was in fact the newly formed company, British Steel Houses Ltd that was responsible for the eventual development and construction of the BISF house we see today.
In 1944 the Interdepartmental Committee on Housing Construction (Burt Committee) shortlisted 2 of the initial BISF prototypes, namely A & B houses for further development at the Ministry of Works Housing Demonstration Site at Northolt Middlesex. After much consideration and a few adjustments to the prototype designs, it was the BISF type 'A' house that went on to gain approval for the erection 34,000 three-bedroom semi-detached houses and 1048 Terraced Houses in England, Scotland and Wales
The prototype 'A' House frame was fabricated from rolled steel sections with roof trusses of rolled steel or tubular sections and the roof was clad with metal sheeting on fibreboard insulation. The lower exterior walls were of traditional brick masonry.
The prototype House 'B' frame was of the same design as the type A frame, but fabricated from flat light steel sections.
The roof trusses also were of light steel sections and the roof cladding was the same as that used in the type A house.
Both types had been designed to accept a variety of external wall materials including traditional brick masonry walls if desired.
Several different floor layouts for the prototype houses were also considered during the developmental stage which can be seen below.
The modified prototype 'A' house was renamed the 'A1' before going into nationwide production in 1944. The final design incorporated render on mesh ground floor walls and profiled steel sheeting to the upper storey section. The preferred roofing material was generally corrugated asbestos cement or corrugated metal sheeting.
The vertically ribbed upper storey cladding was a prominent feature of the BISF house, but unfortunately, it bore a striking resemblance to the cladding profile used on the Hawksley BL8 Temporary Aluminium Bungalow as shown below.
To compound matters further, both systems employed corrugated roofing materials in their design.
The visual similarity caused many to incorrectly assume that the BISF house was simply a semi-detached version of the Hawksley prefabricated bungalow.
Even today, certain members of the public and less well informed professionals continue to assume this to be true, despite the fact that there is no connection whatsoever between these two property types.
The BISF house was designed & built as a permanent dwelling with a lifespan equal to that of a traditional brick-built dwelling.
The house does indeed incorporate a large number of pre-manufactured elements, but unlike the majority of temporary prefab bungalows, it did not arrive on site pre-assembled as a complete dwelling.
The individual components required to build a BISF house were transported in kit form to each site location. They were then bolted together on site, in much the same way as modern commercial steel framed buildings are today. The correct terminology for this type of construction is System built housing.
Temporary prefabs on the other hand, were often pre-manufactured and partially assembled in the factory and transported to site in two complete halves. Each half was lowered onto a foundation pad and simply bolted together by unskilled workers to form a complete house.
There is much debate as to what constitutes a true prefabricated house. This is just one reason why the term System built housing is more commonly used today when describing a property that employs a wide number of pre-manufactured elements in construction.
By The B.I.S.F type A.1 house was to form the mainstay of production. We hold documentation from British Steel Homes Ltd which refers to the erection of 37,000 B.I.S.F. homes in England, Scotland & Wales, with a provided breakdown of 36,052 not including prototypes. There are no records to suggest any were built in Northern Ireland.
Prior to allocation, The Ministry of Health Scotland requested a number of minor alterations to the B.I.S.F. houses they were to receive. To avoid confusion, these units were duly labelled as Type A2 constructions.
The terraced version of the B.I.S.F house, which was built mainly in England, also received minor alterations and subsequently labelled as the type A3.
Below is a partial transcript from British Steel Homes Ltd to an unknown official who had requested further detail in relation to non-traditional steel framed dwellings.
Figures concerning each programme for different types of housing.
We hope to send you shortly, housing returns for England, Wales, and for Scotland. From these booklets you will obtain figures of the total number of houses built during the period 1945 - 48 of steel houses built.
There are several types, e.g. Crudden, Weir and the B.I.S.F. The former two to date have only been built in small quantities, whereas the programming for the B.I.S.F, which is nearly complete, comprises of some 37,000 houses. There are three types of B.I.S.F. houses-
A1 – 30,000.
A2 - 5,000
A3 - 1,056.
Type A1 is the semi-detached type which you visited at Esher
Type A2 has been built In Scotland only and is similar, apart from minor details, to the A1.
Type A3 is a terraced form of house, each block of construction comprising four houses.
The internal fittings of these houses are similar in all respects to Type A1.
General construction detail
The vast majority of BISF houses were built as two-storey semi-detached pairs.
A smaller number of terraced versions were also built by means of framework replication of the standard semi-detached framework.
The description provided below applies to the semi-detached A1 version.
Variations to layout and construction materials have been recorded but in all cases, the original construction and in particular the design & construction of the steel framework remains largely as described.
Foundation & Substructure
A minimum nine-inch brick wall is built on top of concrete strip foundations. These are overlaid with 4in thick in-situ concrete, thickened to 9in where it is carried over the walls.
The steel framework is based on a 3ft 6in module (106.68cm). Stanchions of 4 x 2in RS channel at 3ft 6in centres, except at 7ft nominal window openings in front and rear elevations, extend to roof level in eaves and gable walls. Their base plates are rag-bolted into the concrete plinth.
At first-floor level in the eaves walls, the stanchions are tied by 4 x 3 inch RS angles which support the ends of the floor beams. At eaves level in these walls the stanchions are tied by the outer ceiling joists.
At first-floor level in gable walls the stanchions are tied by the outer floor beam and at eaves level by the collar beam of the roof truss. The corner bays, at the junction of eaves and gable walls, have diagonal bracings of RS angle between stanchions.
The 4 x 1¾ inch RS joist floor beams run at 3ft 6in centres between eaves walls. They are supported near mid-span by a 5 x 3½ inch RS joist spine beam.
At gable walls the ends of the beam are carried on 4 x 3in RS angle trimmer beams spanning between adjacent stanchions. The spine beam is supported across the width of the house by posts at 3ft 6in centres. The posts are made of two 2 x 2in RS angles welded longitudinally to form box sections.
Roof trusses are constructed of RS angle or tubular sections and span the eaves walls. At gable walls the truss is integral with the gable frame. There is a truss each side of the separating wall.
There may be a single or two intermediate trusses. Purlins are of RS angle. Ceiling joists of 3 x 1½ inch RS joists at 3ft 6in centres run at right-angles to the trusses.
Sheeting rails of 2 x l ½ inch RS angle run horizontally on the walls to the first floor at eaves, window-sill and floor levels.
The cavity between the external cladding and internal lining of the external walls is 6 7/8in wide.
The cladding of the walls to the ground floor up to ground-floor window head, is of render on expanded metal mesh. The mesh is tied to the steel stanchions. Above this level the structure is clad in steel sheet which has a vertical, ribbed profile and is fixed to sheeting rails
The internal lining is of 3/8in plasterboard fixed to 2 x 1in timber framing secured to the steel framework. Some upper floor rooms may be lined with hardboard. A paper covered glass-fibre quilt approximately 1 inch thick is sandwiched between the steel framework and timber framing.
Separating (Party) wall
The separating wall is of cavity construction, comprising two leaves of 3in breeze block separated by a 2¾ in cavity. The leaves are tied together with vertical-twist wall ties. In the roof space only one leaf of the wall is continued above first-floor ceiling level and the cavity is closed with asbestos felt.
Internally, the separating wall is sealed with a cement slurry.
The separating wall is lined on both sides with 3/8in plasterboard on timber framing.
The partition walls are non-load bearing and are of timber framing lined with plasterboard or in some instances on both upper and lower floors, with hardboard.
The partitions are bolted to the steel floor beams or spine beam.
The ground floor is usually of solid construction.
The upper floor is generally of 7/8in tongued-and-grooved boarding fixed to 5 x 1¼ inch timber joists at 1ft 6in centres, spanning between the steel floor beams. (there remains one early prototype at Northolt which was constructed with a concrete floor at ground & first floor level).
The ground floor ceiling is of 3/8in plasterboard or fibreboard fixed to the lower face of the timber joists of the first floor.
The first-floor ceiling
3/8in plasterboard or fibreboard fixed to 3 x 1¼ inch timber joists at 1ft 6in centres spanning between the steel ceiling joists. In some instances, the spacing 'of the timber joists differs and fibreboard is used as an alternative to plasterboard.
The roof is clad with asbestos cement profiled sheets carried on purlins supported by the roof trusses. Alternative roof coverings include corrugated steel, corrugated/ smooth profile metal sheeting with the much later addition of lightweight roofing systems such as Metrotile or Decra Tile.
The structural steelwork is painted with two coats of red lead to which a coat of bitumen is added on-site after erection.
The profiled steel sheet cladding is hot-dip galvanised, treated with a mordant and painted with red lead. The sheeting is finished with two coats of a proprietary stone/ masonry paint.
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