Factory-built homes could be the answer to the housing crisis

More homes are urgently needed to avert the housing crisis. One possible solution would be to use more non-traditional building methods - replacing 'bricks-and-mortar' with more industrial methods.

This already seems quite popular in other parts of the world, but although attempts have been made to introduce factory or system-built homes in this country they have never met with wide acceptance.

Often bad publicity has been to blame - for instance the partial collapse of the Ronan Point tower-block or the 'concrete sickness' which affected some post-war system-built homes.

And a single critical TV programme killed off timber-framed construction which had become popular in the 1970's and 1980's. However later research showed the programmes criticisms to have been unfounded, and owners have found no particular problems with homes built using this method.

Developers thinking of adopting non-traditional building methods now face a number of hurdles.

First they must consider whether such methods will be acceptable to the local planning department and will comply with building regulations.

Secondly they must consider whether buyers will be prepared to buy the completed houses.

And in order for buyers to buy the houses they will have to be acceptable as security to mortgage lenders.

This last point has often proved the major sticking point - lenders will want to know that a house on which they are being asked to lend is going to last as long as a traditionally constructed property.

In fact mortgage lenders have not been totally opposed to new construction techniques. But many surveyors face the difficulty of giving satisfactory survey reports because they do not have the experience of looking at properties built using non-traditional methods.

There are certainly a lot of arguments in favour of factory methods of construction. It would help the housing industry and should save time and make homes cheaper.

Traditional house-building construction methods seem to have changed little since Victorian times or even earlier. True there is much more machinery on a modern building site, but visit building sites and you are likely to see a lot of workmen carrying out traditional jobs in the time-honoured way.

But much else has changed in the modern world - most of the goods we buy nowadays have been mass-produced in a factory, often by robots rather than humans. Few people would now want to buy a car which had been made in the same way as they were a hundred years ago!

Already many parts of modern homes such as window frames and roof trusses are made in factories to standard sizes and delivered to site for installation. It would seem a logical step to factory-build the rest of the home as modular units which could then be delivered to the site and simply put together to provide a finished property.

Of course it would still be necessary to prepare the site and provide connections for drains and other services. But construction times could be cut dramatically and far less manual work would be required on-site.

In fact the idea of non-traditional construction has been around for many years. A few homes were built in the 1920's and 1930's using pre-cast or in-situ concrete. A number of steel-framed methods were also developed. But the total number of homes built in this way was very small.

At the end of the Second World War in 1945 there was an urgent need for millions of new homes, both to replace those destroyed by bombing and to replace old slum properties. At the same time there was a shortage of skilled labour in the traditional building trades.

One answer to the problem was the 'prefab' - pre-fabricated factory-built dwellings rather like modern mobile homes, which were intended to provide short-term housing until more permanent homes could be constructed.

Although pooh-poohed by many town planners these prefabs proved remarkably popular with their residents and many had a life far longer than originally planned. In fact some of them were subsequently moved to other sites as holiday homes and are still in use!

For more permanent homes several system-build methods were developed. These often utilised pre-cast panels which could be quickly assembled on site, sometimes on a prefabricated steel frame. Aluminium panels were also used.

The majority of homes built using these methods were owned by local councils, who were therefore responsible for repairs. However when the Right-to-Buy legislation enabled council tenants to buy their homes surveyors often found problems which would have made it difficult for buyers to get a mortgage.

In particular the concrete panels used to build many such homes were found to be suffering from carbonation. Sometimes called 'concrete sickness' this is caused by carbon dioxide in the atmosphere reacting with the cement and reducing the alkalinity of the concrete.

This in turn can cause corrosion in the steel reinforcing bars within the concrete panels, thus affecting the structural integrity of the building.

In order to address these problems legislation was passed and which a company was set up to investigate remedial methods. Following this a number of private companies were authorised to carry out remedial works to homes which had been constructed using a method designated as being defective.

All such works have long since been completed and the properties are now assumed to have the same life-expectancy as conventionally built homes. Consequently they can be purchased without any especial difficulty in getting a mortgage.

Although no steel or timber building systems were found to be defective there were problems in replacing damaged cladding panels as the original manufacturers had ceased production.

Consequently many such properties were re-skinned with traditional (but non load-bearing) walls, and are now indistinguishable on the surface from traditionally built homes.

While these problems with system-built homes received great publicity little attention seems to have been given to the many faults which can arise with so-called traditionally-built properties. Common faults which have arisen in recent years include:

• Lack of lateral bracing to trussed rafters leading to the collapse of roofs
• Corrosion of gang nails used in the manufacture of trussed rafters due to interaction with certain timber preservatives.
• Sulphate attack of mortars in brickwork leading to expansion of brickwork and detachment of renders
• Problems with concrete blocks manufactured from low-grade aggregates. One example of this occurs particularly in Cornwall where blocks using waste from tin-mining, known as 'mundic' can suffer severe failure.
• Weak mortar mixes resulting from either the use of unsuitable sands or from low cement content, resulting in rapid erosion of the mortar from the brickwork and structural instability. (In one case an entire housing estate had to be completely rebuilt!)
• Wall tie corrosion - in severe cases requiring complete re-building of the exterior wall.
• Problems with ingress of water into wall cavities through improperly installed lintels.

Problems of this sort are rarely reported widely, and seem to be accepted almost without question as part and parcel of the construction industry rather than the fault of masonry construction. But when such problems arise with non-traditional construction it is usually perceived as being a fault with the system and all system-building methods are equally condemned.

Factory-built homes can offer many advantages:

• Being constructed in a controlled environment materials are not exposed to rain, sun or other weather conditions as they are on an open building site.
• They can also incorporate very high levels of energy efficiency and comply with zero-carbon standards.
• Factory-built houses can be supplied as a ready to live in integrated package, pre-wired and pre-plumbed and with kitchen appliances and bathroom fixtures already installed. Therefore the minimum of on-site work is required before the house is ready for occupation.
• Homes do not have to be uniform in appearance, as computer-controlled machinery can easily produce a wide range of finished designs.

We don't have to be thinking 'mobile homes' here. Many such homes are indistinguishable from traditionally-constructed homes once erected.

Manufactured homes are common in other parts of Europe as well as North America and Australia. So surely the time has now come to re-consider our insular attitude to non-traditional building methods.

The problems which have occurred with some system-build methods in the past are unlikely to re-occur and are no worse than many of those encountered with masonry construction.

We should therefore accept that modern industry can provide perfectly satisfactory homes which are likely to have a similar useful life to traditionally built ones.