Dig Deep, SW, May 2012 - A basement conversion can be the solution to space problems and also add value to your home

1st of May 2012

If you can’t move, improve; or so the saying goes.  If, for whatever reason, moving isn’t on the cards right now, there are plenty of ways you can alter your present accommodation to suit you better.  Basement conversions are becoming increasingly popular as a way to add considerable living space and value to your home.

For househunters too, a property with potential for a basement conversion – or lower ground floor, as they are often referred to – can be an attractive proposition; by digging down you can extend the property without increasing the building’s footprint or falling foul of development restrictions.

With property and land values still increasing in London, taking advantage of the space beneath your home makes a lot of sense.  You could even convert the space into a separate self-contained flat and bring in a rental income.  However, the work involved with converting a basement is considerable, so it’s not an undertaking for the fainthearted.

Basement conversions are ideal in prime property areas, like Central London, where there is a lack of available space to extend above ground and where the costs of moving may be higher.  Up to three or four levels are possible to achieve (the so-called ‘iceberg’ homes, some of which even have subterranean swimming pools) but one level is most common.

The options are to convert an existing basement into living accommodation, which may involve digging down to increase the ceiling height, or you can ‘retro-fit’ a basement, which means digging out from scratch.  Retro-fit basements are a greater challenge and are more costly, requiring research into soil conditions, potential contaminants, water tables and structural loads.  There are various architects, structural engineers and basement contractors who specialize in this kind of work.  Sometimes the work can be carried out from outside, which is less intrusive and makes it easier to continue to live in the property while the work is going on.

Basements can also be extended out under a garden area to increase living space and introduce more light into rooms beneath the house.

Alternatively, a ‘garden room’ can be created on its own, maybe with a rooflight cut into decking above.  If you’re considering a basement conversion, most specialist companies will be happy to visit you at your home to conduct a survey and discuss the various options.  One of the main issues is damp-proofing; systems vary from waterproof paints, render and membranes to extensive drainage systems using sump pumps.  Insulation is another factor which will help to determine ultimate success of the conversion.

How you will use the converted space should be considered early on in the process.  A bathroom, kitchen or bedroom will have different electrical, lighting and plumbing requirements to a media room, office or gym, for example.  As basements rarely have much natural light, many people opt for a light and bright décor, with carefully considered electrical lighting.  A minimalist design also tends to work well. 

If your basement has windows, now is your chance to replace them, not only are they old and leaky, but also to introduce designs that will maximize light and look the part.  Access to the basement is another consideration.  If you’re lucky, the existing stairs will be sufficient, but more often than not these are poorly constructed, narrow and steep, in which case, a new wider, easy to use staircase will need to be introduced into the design – especially if children will be using the basement area too.

Many older properties are suitable for basement conversions, particularly Victorian houses where the space would have been used for laundry or as a coal store.  However, some may not have sufficient foundations, requiring the extra expense of underpinning work.  Even without this, basement conversions don’t come cheap.  Before embarking on such a project, it is important to work out whether it is cost-effective – there is little point spending more money on the conversion than it will add to the value of the property (although compared to the cost of moving, it may still be a viable option).  For this reason, extensive basement extensions are often only worthwhile in prime property areas such as central London.

While most basement conversions don’t need planning permission as the work will only alter the inside of the property, if the exterior will be affected, for example, the addition of new doors or windows, or if the work will involve digging up pavements or the road outside your property, you will need permission from your local council.  Listed buildings also require planning consent.  All structural or extension work needs to comply with current building regulations, covering matters such as fire escapes, damp-proofing, ventilation, electrics, ceiling heights, door and window sizes, and so on.  Neighbours sharing a party wall are also entitled to enquire about subsidence and request a report; it’s best to discuss any work you have planned with your neighbours before digging starts.