Extending Your House Downwards

We have in the past written various articles about ways in which you can maximise the extent and value of your home. We have considered going upwards into the attic, sideways into a garage or backwards into above-ground conversions or extensions. No doubt you have read about the basement conversions being made by the super-rich in fancy areas of London to provide swimming pools, bowling alleys, ballrooms, room for parking cars. This article is aimed at the more realistic target of providing additional accommodation by going down into the ground beneath or adjacent to your house.


From a legal perspective the first thing to consider is any limitations that there may be in the title to your property which restrict or prevent structural alterations or additions. These are particularly prevalent in long-term leases, but also are often to be found in estate developments which may prohibit such works altogether, or at least require the written consent of the developer of the estate or landlord. Once these points are overcome we move on to the rules and regulations that are applicable to such conversions.


Surprisingly, planning permission is not required for a basement conversion provided that no alterations are made to the external appearance of the building, it is not a flat, apartment or tenement, and the basement does not form a separate dwelling. However if the property is a listed building or is in a conservation area then the permitted development does not apply and specific permissions will have to be obtained.


The Permitted Development Order allows enlargement, improvement or other alteration of a house subject to certain provisions, including that the enlarged part of the house would not have more than a single storey and would not extend beyond the rear wall of the original house by more than 3 metres or be within 7 metres of any boundary opposite the rear wall of the house. It has been argued that the addition of a basement would be adding a storey and

therefore the enlarged part of the house would have more than a single storey. Perhaps surprisingly the High Court rejected this argument by deciding that the enlarged parts of the house did not consist of more than a single storey. The super-rich in London and other cities who have room to do so have gone down two, three and even four storeys into the ground, such works proving to be more economical than moving house, particularly bearing in mind the cost of stamp duty land tax these days. A house worth £1.5 million will cost you £93,750 in stamp duty, and if it is worth £2 million then the cost is £153,750.


It is to be recommended that although you do not need planning permission you do contact the local planning authority and seek a “certificate of lawfulness”. This is a very useful piece of evidence when you come to sell in order to demonstrate compliance.


This is an absolute must because there is so much to consider and to comply with. For example, in respect of the existing building underpinning and foundation work may be required alongside such matter as fire escape routes, ceiling height, damp-proofing, ventilation, electrical wiring and water services. In a nutshell, you need professional help. Whereas a basement usually only has one access point in and out of that room, if you are going to use the space as additional living accommodation then you will need to provide an additional means of escape in case of fire. This can take the form of another door or a window, as long as it can be demonstrated that there is another way to get in and out of the basement in the event of fire.


One of the principal reasons why houses have not been constructed with basements is the obvious one of underground water. In Cornwall we are used to a lot of water but much of it is unseen because it is underground. I live in a valley in a remote part of Cornwall where there is no mains water available. We used to pump water out of the stream into a series of tanks via electric pumps to a tank in the attic so as to have gravity-fed water within the house, but this is certainly not ideal because you do not know what has gone into the stream higher up the valley. Eventually we decided to have our water from an underground supply and got a water diviner to advise us where a supply might be found. He simply asked one question: “Where would you like it?”, and so we ended up with a very convenient supply

immediately next to the house, which has to run through a series of filters to factor out natural chemicals. The result is water that is as pure as any you can buy in a bottle. Now imagine that scenario translated into digging a basement, and the steps that would have to be taken to dispose of the water all around you. I am told that it can be done with special building techniques, waterproof membranes and constantly running pumps, with of course a spare set in case the pump fails, and no doubt there are experts in this field. I expect we have all been in old houses that have a basement and the memory of constant dampness lingers on.


If you live in a detached house with plenty of room around it then there is probably no need to consider any impact your basement conversion will have on a neighbouring property. However if your home is attached, semi- or terrace, or perhaps a ground floor flat with an existing cellar, the Party Wall Act is likely to apply. It covers work to be carried out to existing party walls at or astride a boundary where there is a proposed excavation within 3-6 metres of the neighbouring structure dependent upon the depth of the hole or proposed foundations. A complex set of rules is in place for the provision of detailed information to your neighbour who is entitled to the protection of the Party Wall Act at your expense – a topic that has been referred to in previous articles in this magazine.


Apart from your neighbour, who will have to put up with the noise and general disruption of building works, and making sure that you have complied with all the rules and regulations required by the local authority and the Party Wall Act where applicable, you must consider who else has an interest in your property. My advice is to check out the small print in your mortgage terms and conditions where any structural works are to be carried out, and in addition to consult with your insurers and make sure that all work is covered whilst it is being carried out, and in the event that something goes wrong at a later date.


If you need legal help on property matters do get in touch with us here at Busbys on 01288 35 9000.

David Helman, Busbys Solicitors, Bude & Holsworthy.

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