What The BRE Said about BISF Houses

In 1986 the Building Research Establishment compiled a report on the BISF House in conjunction with the Department of the Environment.

The report was written following a 1984/85 review and inspection of a number of different housing types within the UK that were suspected as being defective by design. The majority of the properties found to be defective during this study were in fact PRC (Pre-cast Reinforced Concrete)  houses. The BISF house was found to be Non-Defective and therefore required no Government assistance toward repair.

The BISF House BRE report did highlight a number of issues that were found in a small number of properties but overall the report concluded that despite inspecting many BISF houses, only a very small number were found to be suffering from serious deterioration and that the survey found that many properties were in fact in near original condition, having no deterioration at all. This was particularly evident where properties had been well maintained by their respective owners or landlords.

The report did find a very small number of properties that had suffered from severe corrosion in certain areas, particularly to the corner stanchions and the area around the eaves near to the gable end. However it was noted that these properties were located in very exposed positions and driving wind and rain was considered to be a major factor and particularly where the property had been poorly maintained to avoid water ingress. Overall though, the number of properties found to be in a very poor condition was actually very rare.

Quote:-

” The number of houses thus affected appears to be a small proportion of the total. The majority of BISF Houses are structurally sound and those with deterioration of the structural framework can be relatively simply repaired by cutting out and replacing the affected members”.

However, it is still worth identifying the main areas where deterioration can be found in order to carry out good levels of maintenance and prevention for the future.

The report recorded the form of construction used and the areas and locations where deterioration of structural and non-structural elements could be identified.

Background and identification

The opening paragraph states that initially 30,000 semi-detached BISF houses were earmarked for construction in 1944 following the Burt Committee push to provide immediate alternative housing as a replacement for the large numbers of properties destroyed during WWII. This number swelled to include 1048 Terraced BISF Houses, which were of the exact same construction, simply placed side by side, thus reducing the quantity of materials required at gable ends.  Over 4,000 BISF houses were also built in Scotland although no indication was given to what proportion of these if any were Terraced.

The report states that following the initial build of a number of experimental prototype houses at Northolt, only the BISF type A house went into mass production and despite being manufactured to accommodate a number of external finishing options, (including a brick Skin*), the  vast majority received rendered lower walls and steel profiled sheeting to the upper elevation. Profiled asbestos sheeting was also the most commonly used roofing material.

bisf house strip foundation

Minor Variations in room layouts and construction were noted between properties but the overall, the structural elements remained largely consistent throughout.

Strip Foundation

The concrete strip foundations were were laid into the ground. A 9″ thick brick wall was then laid directly on top of the outer concrete strip forming the main foundation.

Concrete Pad

The area was then overlaid with 4″ (101.6mm) thick layer of in-situ concrete to form a pad. Th depth of this concrete layer was increased up to 9″ (228.6mm) deep where it carried over  the the brickwork as shown in the diagram opposite.

bisf house foundation pad
Image provided for illustration purposes by BISF HOUSE
BISF Foundation pad

Frame

The steel frame is based on a 3ft 6in module.

Stanchions of 4 x 2″ RS channel at 3ft 6″ centres, except at 7ft nominal window openings in front and rear elevations, extend to roof level in eaves and gable walls (see Figures 2a and b).

For illustration purposes
Early stage of BISF house frame erection

The stanchion base plates are ragbolted into the concrete plinth.

At firstfloor level in eaves walls the stanchions are tied by 4 x 3in 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.

Corner Bracing
Image provided by BISF house.com
For illustration purposes

The 4 x 1 3/4″ RS joist floor beams run at 3ft 6″ centres between eaves walls. They are supported near midspan by a 5 x 3 1/2″ RS joist spine beam. At gable walls the ends of the beam are carried on 4 x 3″ RS angle trimmer beams, spanning between adjacent stanchions. The spine beam is supported across the width of the house by posts at 3ft 6″ centres.

The posts are made of two 2 x 2″ RS angles welded longitudinally to form box sections.

Roof trusses are constructed of RS angle or tubular sections and span the eaves walls.

BISF House roof structure
Image provided by BISF house.com
For illustration purposes

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 1 1/2″ RS joists at 3ft 6″ centres run at right-angles to the trusses.

Sheeting rails of 2 x 1 1/2″ RS angle run horizontally on the walls to the first floor at eaves, window-sill and floor levels.

2.4 External walls

The cavity between the external cladding and internal lining of the external walls is 6 7/8″ wide (see Figure 3).

2.4.1 Cladding

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.

2.4.2 Lining

The internal lining is of 3/8″ plasterboard fixed to 2 x 1″ timber framing secured to the steel framework. Some upper floor rooms may be lined with hardboard. A glass-fibre quilt, 1″ thick is sandwiched between the steel framework and timber framing.

2.5 Separating wall

The separating wall is of cavity construction, comprising two leaves of 3in breeze block separated by a 2 3/4″ 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 3/8″ plasterboard on timber framing.

2.6 Partitions

The partition walls are non-loadbearing and are of timber framing lined with plasterboard or, in some instances on the upper floor, with hardboard. (Admin: Hardboard also found on ground floor). The partitions are bolted to the steel floor beams or spine beam.

2.7 Floors

2.7.1 Ground floor

The ground floor is usually of solid construction. ( Admin: Or sometimes a mixture of concrete / quarry tiles to kitchen area and floor boards or parquet flooring to living and dining room area).

2.7.2 First floor

The upper floor is of 7/8in tongued-and-grooved boarding fixed to 5 x 1Xin timber joists at lft bin centres, spanning between the steel floor beams.

2.8 Ceilings

2.8.1 Ceiling to ground floor

The ground floor ceiling is of 3/8in plasterboard fixed to the lower face of the timber joists of the first floor.

2.8.2 Ceiling to first floor

The first-floor ceiling is of 3/8in plasterboard fixed to 3 x 13’ain timber joists at lft bin 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.

2.9 Roof

The roof is clad with asbestos cement profiled sheets carried on purlins supported by the roof trusses. (in some cases, steel/ aluminium profile sheets were fitted).

2.10 Corrosion protection

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 paint.

  1. PERFORMANCE IN USE 3.1 Corrosion

The remainder of the report covers performance in use. It areas other areas that may be subject to degradation or corrosion and provides images to support investigations.

You can purchase a copy of the full report via the Building Research Establishment BRE bookshop HERE

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