BISF houses were created from 1946 onwards by a body called the British Iron and Steel Federation. The idea was to build large numbers of properties quickly, and at relatively low cost after the war.
They were intended to be cheap, durable, and quick to construct. Over time this has led to question marks about durability though, and mortgage lenders often won't lend on BISF properties. This can lead to difficulties when trying to sell (or buy) BISF houses.
BISF houses have proven to be problematic for people who are either selling or buying a home. You may not know your house is BISF, so be aware.