Basement conversion

Not all basement conversions have to be as extreme as that of hedge fund manager Chris Rokos, whose need for high diving has him planning a swimming pool and diving board dug 4 storeys under his Hyde Park residence.  More modest conversions are common in London nowadays as a way of creating extra space within a house, but be warned it is not a case of grabbing a spade and digging, there are many considerations before embarking on the burrowing route.

Advantages

Obviously you get more space. You are in effect creating a whole new floor the same size as your ground floor and as this can be open plan there are many options for use.

The basement is more accessible than a loft conversion would be, making it more appropriate for everyday rooms such as a living space or bedroom. It can also be used to move a bathroom or toilet, freeing up space on another floor.

Basements draw in heat from the surrounding earth and actually make the house more energy efficient, some reports say by as much as 10 per cent. For this reason proposals have been made to relax the planning consent process. (I have taken this fact from Converted: How to extend your home up, down and out by Elizabeth Wilhide, I cannot find any official figures to verify it so don’t take it as gospel)

It is a way to avoid the costs involved with moving house, such as stamp duty and agents fees. You create more space without the need for a move.

Disadvantages

They remain an incredibly expensive way to increase property size for example, a basement of 40-50 square meters would be around £80 - £100 k. It is only really going to be worth it financially on an upper-end property (around £750,000) where your fees for moving would be high.

They have a tendency for damp, which is expensive and tricky to remedy. There are various systems and building techniques to avoid this but they come at a cost.

If you have no basement to start with then you are looking at a very disruptive process and it would be wise to stay out the house during the job.

You will need a surveyor and solicitor to deal with part wall agreements. As your neighbours will be concerned about subsidence you will have to pay any fees they accrue reassuring themselves.

There is likely to be little natural light or air getting in so ventilation will be an issue.

Things to do

Check water table level

Check with a local agent before you start work so that you can assess whether the change will add enough value to cover the cost.

Contact your solicitor for legal advice as to party wall agreements, planning permission and building consent.

Contact an underpinning specialist to get quotes.

Factor in any costs that may be incurred as you seek alternative accommodation during the job, such as hotels.

A quick word on what not to do

Do not follow in the footsteps of one of my personal heroes, the Moleman. For 40 years he has been digging his own cellar at 121 Mortimer Road in Hackney, east London (actually whingy neighbours and an interfering council have put a stop to it now.

It is probably best to get a professional in…but then again it is people like the Moleman that make this whole silly muddle of a life bearable, so go ahead do it yourself. (oh and as a side point the Moleman managed 26ft deep, millionaire hedgefund manager 16ft. Not that I am passing any judgment, just thought I would point it out)