BISF 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 BISF house is NOT and has never been classed as defective under the housing act. 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 the ‘real’ prefabricated, temporary life-span buildings that were built in large quantities across the country. Although many temporary prefabs still stand today, the construction methods used to build these dwellings is quite different from those used to build the British Iron and Steel Federation house. The main similarity was the use of prefabricated steel panels and asbestos roofing sheets on the outside of the houses. Outwardly the properties appeared very similar, giving rise to the common and wrongly used term prefabs for BISF homes.
This term was not only adopted by the public but also by surveyors, insurance companies and lenders based largely on a lack of familiarity and understanding of BISF construction. Regular readers of BISF house.com will recall our previous article showing how even mortgage companies get their BISF facts confused, wrongly classifying them as defective under the housing act 1984. 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.
Certain PRC type houses have a defect known as ‘concrete cancer’.
These 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 and causing them to be classed as defective under the housing act.
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 not immune.
BISF houses do suffer from a number of specific problems which tend to be due to poor maintenance and not always defective production or design. Similar low quality steel may or may not have been used to build the supporting frame of a BISF house but unlike a PRC property, the steel used in a BISF house was never encased in contaminated concrete or it 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 exposed parts such as bolts and other fixings.
Corrosion can occur particularly on the outer corners of the BISF frame where the steel legs or stanchions are fixed to the concrete footing platform as can be seen in the image here.
This is particularly evident in cases where the ground floor render has cracked allowing water and moisture to enter the cavity.
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 see here.When we consider that these stanchions have been in place for almost 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 not easily seen.
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.