With our diminishing building space and fast rising land prices, the return of the basement makes sound economic sense. So why are they still so rare in new houses in the UK?

Basements were fashionable with the Victorians and Edwardians when labour to dig the cellars was cheap, but with the coming of World War One the rate of building fell dramatically. After the war the number of household servants radically diminished so the need for accommodation below stairs was greatly reduced. With the rush to the newly-expanding suburbs in the 1920s and 30s, thanks to improved public transport, more land became available for building and so the need for below ground accommodation diminished.

Today it is estimated that less than two per cent of new homes being built in the UK have basements, although as many as seven per cent make use of sloping sites to build a partially submerged basement. Nevertheless they are becoming less rare according to Alan Tovey of the Basement Information Centre. “Many self builders are seeing the obvious advantages of going down to provide extra space as plots get smaller and more expensive,” he says.

“However, the real impact will come when the volume housebuilders move into basements. At present they perceive them as simply an extra cost, but new planning directives from the government plus Westminsters drive to increase housing densities will, I am sure, nudge more and more housebuilders in the direction of basements.”

What are the Benefits of a Basement Conversion?

More Space, Same Footprint

It has been estimated that in the UK we need 4 million new homes in the next 20 years, so naturally one important option when it comes to using our available building land better is to go down. By adding a basement to a two storey house you can get as much as 50 per cent more floor area without having to increase the size of the footprint or having to sacrifice any more garden.

Growing Families

Basements have a big appeal for growing families who do not want to move house.If a basement is an option it means you can stay in a home you love, in an area where you have already put down roots.

Better Site Utilisation

If you are having to dig deep foundations for any reason, it might make economic sense to add a basement. Deeper foundations cost more, so turning this expense into useable space makes sense.

Use a Sloping Site

Basements can also make good use of a sloping site. Rather than level it why not create a semi-basement, if necessary by doing a cut and fill, digging out from the slope and then levelling to form a firm base upon which to build?

Gaining Extra Space

Basements can be a good way of gaining extra space in sensitive sites where there are height restrictions. A full basement can mean the house can benefit from an additional storey, without having to raise the ridge height of the roof.

Energy Efficiency

A house with a basement has fewer directly exposed external walls.

Wall and floor insulation are improved and the means of construction incorporates additional mass. The effect of this is that the building does not overheat or cool down too fast. It therefore helps to retain heat and to control fluctuations in temperature. This is why the Basement Development Group says that a house with a basement can be up to 10 per cent more thermally efficient than one built entirely above ground and will also bring about savings in the quantity of insulation material needed.

Multi-purpose use

One of the joys of a standard basement is that it can be used for a variety of purposes and graduate from being a children’s playroom to a television and games room for them when they grow older. Unusual specialist uses include basements specifically designed to provide swimming pools or wine cellars.

What are the Cons of Including a Basement?

Not an Option Where There is a High Water Table

The British Structural Waterproofing Association and the British Cement Association do not recommend building basements particularly those that rely entirely on tanked protection on sites where the water table is too high. This is defined in the Waterproofing Design Guide (available from the Basement Development Group) as where the water table is above the underside of the lowest basement floor slab. A very useful risk assessment chart is printed in the guide.

Problems of this type are likely to occur when a head of water brings pressure to bear on the walls of a basement. If there is an external membrane for waterproofing it is always possible you might get a leak. A hydrostatic head is totally different from percolation of water. A head of water refers to depth, so if, for example, a burst water main were to saturate the ground on the outside of the basement, the head of water would reach the top of the basement walls.

If you have a leak in the membrane it should be easier to carry out repairs if it is fixed inside rather than outside the structure. It is possible to open up external systems for inspection, but this may not be practical if there is hardstanding above or, as is often the case, where the basement is partial that is, beneath only a part-section of the house.

You Might Struggle to Find Professionals for the Job

One other potential drawback is that if you are contemplating a basement in your new self build you might find your favourite architect may not be willing to take on the brief. The reason is likely to be fear of litigation should the basement fail.

One architect in a small partnership says: “If there is a failure they fear the client might take them and the structural engineer to court.” A number of very famous architects, including Frank Lloyd Wright, were against basements beneath houses. In this country it is generally the smaller practices who are against building basements in domestic schemes on the basis of: why take the risk? In towns where basements in new buildings are the norm, the big practices are usually quite able to cope.

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