Non-standard construction

What is a BISF house, and why is the frame a survey question?

A BISF house is a post-war steel-framed house, named after the British Iron and Steel Federation system. The frame, not a conventional brick cavity, is what carries the building. A survey should say if that is what the surveyor believes they are looking at. It cannot, from the cladding alone, prove the steel is sound.

Last reviewed 24 October 2026. Written for buyers in England and Wales unless this answer says otherwise. No named surveyor has signed this page. It is general guidance, not a report on your house, and not legal advice.

What is the fuller explanation?

Steel frames corrode where they stay damp, especially at the feet and behind cladding. A visual survey looks at the cladding, the junctions and any staining or distortion. It does not remove panels as standard, and it does not scan the steel. Calling it “non-standard” without the system name makes the next conversation with a lender harder, because lenders ask which system, not whether the house feels solid.

BISF construction is not the same sentence as a designated defective precast-concrete house. Do not let the two labels be swapped in a mortgage application. Ask the surveyor which system they mean, ask the lender whether they lend on it, and only then decide whether a specialist inspection of the frame is justified. There is no RICS national price for that inspection.

What should you ask your surveyor?

Are you identifying a BISF frame, or only saying the house is non-traditional?
What could you see of the steel, if anything?
What should we ask a lender before we treat this like a brick cavity semi?

What are the typical next steps?

Tell the lender the construction the surveyor has named, in the surveyor’s words.
Do not clad over the frame to make it look like a cavity wall before the lender has answered.
If the system is only a suspicion, ask for the evidence: the roof form, the cladding, the party wall. Do not invent a label.

Costs vary with the building and with who you instruct. Where this page does not cite a published figure, ask the surveyor, a relevant specialist, or your solicitor for a written quote. Do not treat a forum average as the price.

Also asked about this

Is every steel-clad house a BISF?

No. Several systems used steel. The name matters. If the surveyor is not sure, they should say they are not sure.

Does a brick skin mean the frame has gone?

No. Brick or render can be a cladding in front of steel. Ask what is behind it. The survey may not have opened it.