On another level

Brian Davison of Delta Membrane Systems delves into the benefits of including a basement in a property, and advises on how to prevent water damage.

When asked in what type of house you would usually find a basement, the average person would think of a multi-storey property, probably terraced, and built in the Victorian era, perhaps slightly later.

The picture many have in their minds when it comes to basements is a damp area, illuminated by a solitary light bulb. Because of this, basements are often considered a relic from times gone by, a dank place where a rickety old boiler rattles away in an effort to keep to the house warm, or where all those old photographs are kept – the dumping ground for worn-out cardboard boxes.

While many perceive basements as serving little or no use, there is a strong argument to include basement areas on new-build developments, the most prominent being the ability to increase usable living space.

Land that might once have been ignored, seen as unsuitable for construction, is now ‘in the frame’. With developers currently pushing through as many properties as possible onto a plot, the negative effect of smaller and more compact housing is being seen across the country, and is particularly acute in London.

In situations such as these, creating extra space without a detrimental effect on the ecology of a dwelling will always be be of benefit to the homeowner. In larger, more exclusive sites, a basement can be the ideal place for a ‘granny annex’, wine cellar, gymnasium, home cinema, or play area for kids and grown-ups alike.

When it comes to construction, instinctively the thought process is to ensure moisture from the outside is prevented from ingressing into the building, but that need not be the case. The most common solution for below ground construction would be tanking, the application of a layer of cementitious waterproof render on the walls, likened to a waterproof screed on the floor. This can also be achieved by using a sheet membrane, asphalt or other liquid-applied waterproofing material.

Hydrostatic pressure, the external water pressure around the basement, is another critical factor. It is crucial that the tanking be securely fixed to the substrate, as the pressure from the water table around the basement can be significant. Hydrostatic pressure will force water through tiny gaps very quickly, so great care should be taken at this stage to ensure that the waterproofing meets the demands made of it.

Many argue that rather than doing your utmost to prevent water entering the building, with a real possibility of failure, it would be more beneficial to deal with the water once it has entered the building. This is how the problem is often dealt with in refurbishment situations. Cavity membranes with a studded profile are used on the internal face of the walls and concrete floors to form a waterproof structure. The studded side is placed against the wall and the floor to create an area that allows water to flow down to the floor and into a drainage channel to a sump. It is then pumped out to a suitable drainage outlet.

Compared to the tanking options, this is a relatively straightforward and cost-effective solution to dealing with the water that seems to inevitably find its way into a building. The method has been used on countless properties, domestic and commercial, in both new build and refurbishment applications.

There is no escaping the fact that a well-built and finished basement area has the potential to bring much more usable space to a property, and there is no need whatsoever for this space to quickly become redundant.

The extra space a basement brings, all within the footprint of the land parcel, can be invaluable, and is one way of bringing added value that will remain with a property for decades to come. Basements might have been a thing of the past, but they also have a real future in the modern housing market.

Advice on all aspects of basements is offered by the Basement Information Centre, particularly in its publication ‘Guidance Document – Basements for Dwellings’. This is an essential read for those new to this type of work, as it provides practical guidance on meeting the relevant requirements in Schedule 1 of the Building Regulations.

Brian Davison is managing director of Delta Membrane Systems.