BISF (British Iron & Steel Federation built) Steel Frame House – Defective or Not?
Following the post war housing shortage of the 1940’s, thousands of homes were built across the width and breadth of the country using a range of new and unproven building methods. Many of these houses have since been demolished or have suffered from serious structural defects making them potentially unsafe and in some cases very difficult to obtain mortgages on unless they have been fully repaired. A large number of these non traditionally constructed houses have been officially classified as defective under the housing defects act 1984 and government funds have since been made available to repair them. PRC or precast concrete houses are just one example of the many that are listed.
The British Iron & Steel Federation House is NOT, and has never been, classified as defective under the Defective Housing Act, 1985. In fact, the BISF House has emerged as one of the most successful System Built dwellings of the post war construction era.
All too often BISF houses are wrongly classified as ‘Prefabs’ and placed into the same category as what one could loosely describe as a ‘real prefab.’ i.e Prefabricated, temporary life-span buildings (frequently bungalows) that were built in large quantities across the country, after WWII. Although many temporary prefabs still stand today, the construction methods used to build these dwellings was quite different from those used to build the British Iron and Steel Federation house. Two visual similarities however, did cause some confusion between the two properties. The BISF house did incorporate the use of prefabricated steel panels and asbestos roofing sheets to the exterior of the house, and thus, outwardly at least, the properties did appear to look very similar externally. This lead to many people making the wrong assumption that the BISF house was simply a semi-detached version of the temporary prefabricated bungalow. This is just one reason why the BISF was wrongly labelled by so many as being a ‘Prefabricated house’.
The term ‘prefab’ for a BISF house was not only adopted by the public, but also by surveyors, insurance companies and lenders too, based largely on a lack of familiarity and understanding of BISF construction. Regular readers of Non Standard House.com will recall our previous article showing how even mortgage companies get their BISF facts totally confused by incorrectly classifying BISF houses as defective, under the Housing Defects Act legislation 1984/5. See Post HERE
To say that BISF houses are problem free would be wrong.
Many post war houses are considered to have ‘inherent defects’. In simple terms this means, a defect in the building which is a product of improper construction or design.
For example, certain PRC (Precast Reinforced Concrete) type houses have a defect known as ‘concrete cancer’.
Such PRC houses were built using a system of steel reinforced concrete panels, but contaminates present inside the concrete has caused devastating damage to the inner steel reinforcing bars or rebars. Severe corrosion and crumbling concrete caused by the chemical contaminates has weakened entire structures causing them to be classed as defective under the afore mentioned Housing Act defects legislation.
Poor quality steel was also a contributing factor and was widely used in post war construction due to raw material shortages. Todays higher quality steel is more resilient to corrosion and attack by compounds, but it is still not always immune from the effects.
BISF houses do suffer from a number of specific problems which tend to be caused by poor maintenance rather than defective production or design. Similar low quality steel may or may not have been used to build the supporting frames of BISF houses, but unlike in the case of PRC properties, the steel used in the construction of BISF houses, was never encased in contaminated concrete, otherwise these houses could well have suffered a similar fate.
This does not mean that the BISF steel frame is immune to its own specific problems.
Steel in any shape or form needs to be protected from corrosion, caused by contact with moisture. A protective anti-corrosion coating is often all that is required, but inevitably this coating can become breached by handling during construction, or when first applied, it may not have covered all of the exposed parts, such as the bolts or other fixings.
Corrosion of the BISF house steel structure can occur. Where present, It is most frequently observed to occur at the base of the steel stanchions, located under the wall render on the outer corners of the Gable end wall. This is the point where the steel legs or stanchions are bolted down onto the concrete footing platform, and where moisture is most likely to collect.
This is particularly evident in cases where the ground floor exterior wall render has cracked, allowing water penetration and occasionally pooling.
Condensation caused by poor insulation and lack of ventilation can also accelerate corrosion. When warm moist air inside the house condenses onto the cold steel surface in sufficient quantities, it can soon run down to the lowest part of the frame and significantly accelerate corrosion.
This column would need replacing by cutting out the badly corroded section and replacing it with a new section of treated steel. The process itself is not difficult but would normally need the services of a builder and structural engineer who have experience with this type of repair.
The image to the right shows a repaired steel stanchion.
The corroded steel has been cut away from the foot, leaving only sound steel above. A new base plate and supporting steel column have been welded together and inserted directly under the existing column which has also been fitted with a base plate for added support.This new section will then be coated with a corrosion resistant coating to protect it from further corrosion.
Severe corrosion of the frame is very rare – But it can occur, as we seen.
When we consider that these stanchions have been in place for over 70 years, it is hardly surprising that some will need inspection and repair.
Fortunately this is not a very common problem, unfortunately the stanchions are hidden underneath render or brickwork and are not easily seen or accessed.
It is worth ensuring that the lower part of a BISF house is well maintained and any cracked or damaged render should be repaired quickly to avoid water penetration. Remember that standard render must not be applied. A flexible or treated render should be used that will allow some movement and prevent cracking. You should also check the property for signs of cracking to the concrete foundation pad, paying particular attention to the corners of the property at ground level if visible. Any sign of disintegrating or cracking concrete may well need further inspection. Remember to always use qualified tradesmen who are familiar with BISF construction and have a proven record or valid references.