Earlier in the year, a Georgian terraced house which belonged to a former Phones4U CEO collapsed without warning. The owner was having a cinema, gym and wine storage room built in the basement when both an outer wall and two storeys fell into the street. Luckily there were no injuries, but let’s hope the owner was fully insured. Not that Georgian houses were exactly solid when built – newly built houses collapsing because of inadequate foundations happened quite often in Georgian London.

Unqualified Builders Piling in

However, it does emphasise yet again the need to employ a basement conversion company that knows what it’s doing. This is particularly relevant at the moment, when there is a strong temptation to wing it with a general builder who says they’ve dug out a basement before.

The reason it’s tempting to go with a risky proposition is that the boom in basement conversion in London means a lot of builders are trying to get in on the act. They can appear to talk the talk about structural engineers, and their prices will almost certainly be lower than employing a full service firm.

But what do they actually know about the water table in your area? Or how to install a sump pump properly? Or whether your plans for your existing cellar do or don’t require planning permission?

Complex Projects Unsuitable for General Builders

Basement conversions are complex projects, in which a number of specialists bring their knowledge together to create a plan that is safe, achievable, robust and will stand the test of time.

Most basement conversion projects take place beneath terraced houses because they are the ones with no room to extend or expand. However, it’s important to note that because the wall is shared with the house on each side of you, the provisions of the Party Wall Act apply. Do you know how to serve a Party Wall notice? Does your builder? It’s just one of dozens of pieces of regulation and compliance that are required, and yet another reason why specialist basement conversion practices are the only sensible choice.

After all, the difficult bit is not the digging! Anyone can hire a digger and start excavating. It’s the other stuff that tends to cause the problems – advanced understanding of the structure’s tolerances, for example, or what a methods statement is (not something even a good general builder will necessarily know about). And in 2015, 50% of basement building sites inspected by the Health and Safety Executive failed a safety inspection.

So how to steer your way through this maze? Look for a company that sees quality assurance as the steering principle of its work. This points to experts, who understand how important sound systems of work and proper knowledge are. If you can, find someone who is a full member of the British Structural Waterproofing Association. The BSWA is hot on standards of work and expertise, and if your chosen firm is a full member, it should offer you some peace of mind.