What it is
BISF houses take their name from the British Iron and Steel Federation. They were built in the late 1940s, often as semi-detached pairs for councils, as one of several ways to build homes quickly at a time when bricks and skilled building labour were short.
The structure is a light steel frame of columns and beams that carries the floors and roof. In the original form, the ground-floor walls were rendered and the upper walls were clad in profiled steel sheeting. Inside, the frame is hidden behind linings. Because the frame carries the house, its condition is central to any assessment, yet it is the part a visual survey can see least.
Many BISF houses have been changed since they were built. The steel sheeting may have been replaced or covered over, insulation added to the outside, windows replaced and roofs re-covered. Some now look very different from the original design.
How to recognise it
- In the original form, a rendered ground floor with profiled metal sheeting on the upper walls.
- Houses of the same design nearby, some in original condition and some altered.
- Steel frame members that may be visible in the roof space.
- Walls that sound hollow when you tap them inside, because they are lined rather than plastered masonry.
- An EPC that describes the walls as "system built".
Over-clad houses can be hard to identify from outside, so the roof space and the paperwork matter.
Common problems
- Corrosion at the base of the columns. The steel columns run down to ground-floor level. Where damp collects there, for example because ground or paths have been raised against the walls or water has been getting in, the steel can rust. Loss of steel at the column bases is a key concern for engineers and lenders.
- Cladding and render. Rusting or damaged steel sheeting, cracked render and failed joints let water in, and water that gets behind the cladding can reach the frame.
- Roofs and rainwater. Roof leaks and overflowing gutters can direct water onto the frame for years before any sign shows inside.
- Insulation and condensation. The original walls were thin and poorly insulated by today's standards. Upgrades help, but if they are badly detailed, moisture can be trapped against the steel.
- Alterations. Cutting into the frame, for example to form a larger opening or attach an extension, should be designed by a structural engineer.
- Materials of the period. Asbestos can be found in any building built before 2000, so get an asbestos survey before any work that disturbs old materials.
Mortgages and insurance
BISF houses were not designated defective, but lenders treat them as non-standard. Some will lend, often with conditions such as a satisfactory structural engineer's report or evidence of refurbishment work. Others will not lend on them at all. Policies change, so check with your lender or broker before you pay for a survey.
Tell your insurer the construction type, and ask your conveyancer to check the paperwork for any over-cladding, insulation or structural repairs.
What we check
In a Level 3 Building Survey of a BISF house we:
- identify the construction and any refurbishment, as far as a visual inspection allows
- look for rust staining, bulging or cracked render, damaged sheeting and damp near ground level
- compare outside ground levels with the base of the walls, and check how rainwater is carried away
- inspect the roof space, where parts of the frame may be visible
- use a drone to look at the roof and gutters, where flight is permitted
- ask for any engineer's reports, refurbishment details and guarantees
We cannot see the bases of the columns without opening up the walls. Where the condition of the frame is uncertain, or your lender asks for it, we recommend a structural engineer, who may open small areas to inspect the steel. Our report explains what we could and could not see, so that you, your lender and any engineer know where to look.
What we have found locally
BISF houses appear only occasionally in our survey reports.
Reports that recorded BISF construction:
1 DBISS survey report since 2022
For other steel-framed designs, see our steel-framed houses guide.
Sources
- Hansard: Housing Defects Bill, second reading, House of Commons, 26 April 1984, which lists the PRC types to be designated
- RICS: Home Survey Standard
- BRE: SAP 10 and RdSAP 10 specifications, which define the wall types used on EPCs
- Health and Safety Executive: Asbestos