BISF refurbishment. BISF properties were homes that were designed and built by the British Iron and Steel Federation. The organisation was actually formed back in 1934 but it wasn’t until after the second world war that it diversified into housing by signing up to the Ministry of Works Emergency Factory Made Housing Programme.
By enlisting the support of renown architect Sir Frederick Gibberd they came up with a Ministry of Works approved permanent steel framed house design that we know today as simply the BISF house.
In total there were over 35,000 BISFs built in the UK from between 1944 and 1950 – all two storey semi-detached or terrace houses. They are one of the easier types of non-trad properties to identify due to the fact they incorporate a vertically profiled steel sheet to clad the upper floor of the property which we affectionately know these days as “wrinkly tin”!
As you’d expect the main frame structure comprises of steel columns. In total there are spaced RSC stanchions, double RSA single storey stanchions (typically 17 or 19 in number), RSJ floor support beams, RSA floor joist supports, RSJ floor joists, ceiling joists, tubular steel floor trusses, a mock truss and RSA purlins and cladding rails. The frame was coated for protection with red lead or black bituminous paint. The frame was specifically spaced to take steel framed windows. The ground floor windows were a particularly large size.
Separating walls were of cavity construction and built with concrete breeze block which were faced with a timber frame lined with plasterboard. In the roof space the separating wall was a single leaf block.
Externally the ground floor finish to most BISFs consisted of a thick render applied onto to expanded metal lathing. There are some variants with were finished with brick and block cavity wall, vertically profiled asbestos sheets The upper floor, as mentioned earlier, was finished externally with a vertically profiled steel sheet which were originally galvanised and coated with a red lead paint – although many now have been repainted in various colours.
The roof was a shallow pitch gable design with was finished with profiled asbestos cement or steel sheets.
You will often find these BISFs have a single storey lean-to attached to the gable wall.
Areas of Concern
As you’d expect, because there’s a lot of metal work used in the construction of a BISF house corrosion is the biggest area of concern.
- Specifically you should look for corrosion to the RSA and the RSC stanchions – especially around the corners and at the base.
- Corrosion of the rails holding the sheeting needs to be examined.
- The metal lath holding the render will likely have corroded. This will result in render failure.
- The profiled steel sheets along with any steel flashings are also prone to corrosion.
- Check for cracking to ground floor slabs – especially in the corners.
- Extra care is needed when checking for deterioration of any profiled asbestos cement sheets used on the roof
As you will see from some of the before and after images, BISF refurbishment can be transformational to both individual properties and communities as a whole. The profiled steel sheeting that we associate with all these properties looks incredibly cheap and dated. It’s also highly inefficient from a thermal perspective too. It’s therefore possible to make these properies look modern and new whilst also improving thermal efficiency dramatically.
As with any non-trad refurbishment project – it shoudl always start with a full structural survey. The steel fame should be examined for any corrosion and repaired accordingly. The Structherm technical team will then get to work on a full specification for teh refurbishment works.
Typically this will incorporate the unique Structural External Wall Insulation system (SEWI) which is designed to fix into the steel frame itself and therefore span the existing substrates which can either be removed or left in place. You can read more about the SEWI system here.
The SEWI system adds both structural integrity and thermal efficiency. It also provided a base for a wide variety of modern finishes, textures, effects and colours. This could be brick effect render, standard through colour render in a variety of textures or a dry aggregate dash. It could (and often is) also be a combination of different finishes.