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Houses of Non-Traditional Construction – Common Property Defects #6

Sunday, 20th March 2016 | by: Steve Hobbs

We have recently completed a number of pre-purchase surveys for clients intending to buy houses of non-traditional construction. Properties of non-traditional construction can often be a source of concern for buyers and mortgage lenders alike, as some suffer defects not found in the general housing stock, and might require expensive repairs.

As industrialisation swept the nation in the first half of the 20th Century, and wages began to outweigh the costs of materials in the construction process, the attention of developers turned to processes designed to increase efficiency and speed on site. The earliest system-built houses date back to the inter-war period, when around 50,000 non-traditional dwellings were built. However, it was during the post-war period that production stepped up a gear. Between 1945 and 1955 around 20% of new housing was system-built, amounting to some 500,000 units, with a further 750,000 units being constructed between 1955 and 1970.

In the 1970s there was a reaction against system-building, due primarily to issues of poor design and construction that came to light as defects in the houses built during the 1940s and 1950s began to appear. A number of dwellings suffered from problems with thermal insulation, noise insulation and condensation, and in some cases failure of external cladding and structural components. The government introduced legislation under the Housing Defects Act 1984, which allowed local authorities to designate particular types of property as ‘defective by reason of their design or construction’, and fund remedial work. In total, 26 specific systems were designated defective.

There are a large number of different systems that have been employed over the years, each of which are unique and have their own list of potential defects (not to discount a number which have performed satisfactorily). In general, they can be classified as steel framed, timber framed, precast reinforced concrete construction, and cast in-situ concrete construction.

Concrete Systems

Concrete systems can be broadly classified as being of precast reinforced concrete construction, or cast in-situ concrete construction. Precast reinforced concrete systems were manufactured off-site, and ‘slotted together’ on-site, whilst cast in-situ concrete systems were poured on-site into a timber ‘formwork’ called shuttering.

Concrete system-built houses can be hard to identify. Many have been refurbished, with rendered finishes, new roofs and replacement windows, masking the characteristics of the original building. Chimney stacks built of concrete blocks or mass concrete are an indication that the house may be of concrete construction. Usually, this can be confirmed by inspecting the party walls in the roof space, which are not covered by external renders or internal decorations.

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One of the earliest examples of caste in-situ concrete construction; this terrace in Brockley, South London, was built by the Edwards Construction Company in the 1920s. The walls consists of an inner and outer leaf, tied together with special walls ties. Whist there are not obvious signs in this terrace, the reinforcements in a number of examples have been found to have suffered corrosion, particularly in exposed locations. From the exterior, the only indication of the form of construction is the concrete chimney stacks (top and bottom left). The concrete party wall can be seen in the roof space (bottom right).

The primary concern in houses of concrete construction is carbonisation of the concrete, which can result in the reinforcing steels rusting, compromising the building’s structural integrity. Generally, carbonisation is a greater issue in buildings of precast reinforced concrete construction, due to the use of poor-quality concrete, and reinforcing steels being placed at insufficient depths within the concrete.  The process is accelerated by water penetration, so buildings in exposed locations or with compromised weather-tightness can be particularly vulnerable. Carbonisation can also be caused by calcium chloride, which was commonly added to concrete up until the 1970s. Corrosion of the reinforcing steels will often manifest itself as longitudinal cracking in the external finish of the wall, accompanied by spalling and splitting of the concrete, revealing the reinforcements below. In extreme cases there may be bulging and leaning of the external walls as the building begins to lose its structural integrity.
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Top left; this ‘Unity’ house in Leyton, East London, is of precast reinforced concrete construction. The loads are carried by vertical precast reinforced concrete columns, with inner and outer leafs of precast concrete blocks. Common defects include rusting of the fixings between the joists and columns, and carbonisation of the concrete leading to degradation of the reinforcing steels, resulting in complete structural failure. Unsurprisingly, Unity houses are designated defective under the Housing Defects Act 1984, and as such are only mortgageable if they have been subject to an authorised repair scheme. Top right; a house on the same estate which has been repaired. The work involved removing the outer leaf of blockwork and reinforced concrete columns, before constructing new external brick-faced cavity walls. The owner described the process as “removing the cancer of the house”.

A further area of concern in both pre-cast concrete and cast in-situ systems is the quality of thermal performance, which tends to be poor. A large number of concrete houses have been found to suffer from excessive heat loss, surface condensation leading to mould growth, and rainwater penetration.

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Top left; a house we recently surveyed in Slough, of Wimpey ‘no fines’ construction. Built by the Wimpey company in the early 1950s, the houses are so called due to the use of cast in-situ ‘no fines’ concrete (concrete made up of cement and graded aggregate, but no sand or other fine aggregate). ‘No fines’ houses have better thermal efficiency than many other concrete dwellings, due to the internal pore structure of the concrete. However, thermal performance can still be an issue. A neighbouring house (top right) has had an external render system applied to improve thermal efficiency.

Steel Framed Systems

Perhaps controversially, no steel framed houses were designated as defective under the Housing Defects Act 1984. That is not to say, however, that this form of construction has not been associated with unacceptably poor performance.

The largest provider of steel framed housing was the British Iron and Steel Federation. British Iron and Steel Federation houses that have not been subsequently altered are easy to spot, as the elevations were clad in steel sheets. The houses had asbestos roof coverings, which tend to become brittle and lose their structural integrity with age, posing a risk to the building’s inhabitants, as well as compromising weather-tightness.

The primary concern when dealing with steel framed dwellings is the potential for corrosion of the frame; particularly the vertical corner members, where the cladding or render may be less effective. Worrying signs include cracking to rendered finishes or heavy corrosion of steel cladding. Again, thermal performance can also be a problem.
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This house in Winchmore Hill, North London, appears, from the outside, to be of typical cross wall construction. However, inspection of the roof space (bottom left) revealed that the building was in fact steel framed. At the request of the buyer, the vendor agreed to have some of the brickwork removed at the flank corners to allow for inspection of the frame, which they were relieved to find remains in acceptable condition (bottom right).

Timber Framed Systems

Timber framed houses have been in existence for many hundreds of years.  However, there are a number of specific issues with those constructed in the in the 1940s, 50s and 60s (since when construction techniques and systems have improved significantly).

The houses were typically clad in brick or in timber. Sometimes, party walls were of brick (called cross wall construction), with the frame forming the front and rear elevations. The frame is typically sheathed in plywood, nailed or stapled to the members of the frame, to provide extra rigidity.

Defects are, perhaps unsurprisingly, typically related to moisture and consequent timber decay. Moisture ingress can result from impaired weather-tightness. Condensation also poses a risk. A vapour check should be fitted behind the internal decorative finish of the walls, but in many cases, the vapour check has been found to be poorly fitted, or subsequently inadvertently damaged by the homeowner or tradesmen whilst carrying out minor internal works. Likewise, fully insulated cavities can result in a build-up of moisture within the wall. A further area of concern in brick clad examples is differential movement between the timber frame and brickwork, resulting in cracking and sometimes bowing of the brick outer skin.

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An example of cross wall coonsruction in Blackheath, South London. The front and rear elevations are timber framed and clad in weather boarding. Structural loads are carried by the brick-built party walls.

Mortgagability

The ability to raise mortgage finance against a house can be an area of concern for potential buyers of non-traditional houses. Even cash buyers may be worried that the future saleability of their property could be compromised if the property is declined for lending purposes. Each lender has its own specific set of requirements, and there are a number of houses not found on the designated defective list that are still considered unacceptable for loan security. Generally speaking, issues of mortgageability are likely to be encountered with precast reinforced concrete homes that have not been subject to an approved repair scheme, cast in-situ concrete houses that are badly cracked, timber framed houses built between 1945 and 1970, and those with fully insulated cavities regardless of age. Others, such as many steel framed houses, may be acceptable for loan security subject to a full building survey.

Conclusions

The present stock of system-built houses contains many types, a number of which, particularly those built in the post-war period, have underperformed, and sometimes developed serious defects. However, the performance of some others has been generally satisfactory, and in many cases, even where defects or other issues such as poor thermal performance do exist, the required repairs or remedial works may be prohibitively expensive.

Consequently, each property needs to be assessed on an individual basis, taking into account the form of construction, and the risks of any associated defects. If you are considering buying, or already own a house of non-traditional construction, and require further advice, our Chartered Surveyors will be happy to help. You can contact the team on 020 7183 2578 or by email.