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Basements

It is very common in northern Europe, especially Scandinavia, to see the semi-basement flat configuration where the window sills are at ground level and this effectively creates an extra story without making the building much taller. Alternately these areas may be used for utility rooms, storage or, if the contours permit, garaging.

It is quite a mystery why the cellar, which was so common in traditional UK buildings, particularly in the Georgian, Victorian and Edwardian periods, has not been carried on with and developed into a dry basement. This is particularly strange when you consider the high price of building land and the high demand for storage space.

A semi basement area is effectively partly earth sheltered and therefore requires less heating if insulated and unlikely to suffer from frost if not.

One or two of the German timber kit house importers now offer the option of a prefabricated basement room. Glattharr even have a floating show house to prove the waterproof standards of their construction methods!

Another, cheaper approach is the more traditional cellar which is not moisture proofed but can be used for storage provided items are kept dry by wrapping in plastic or whatever, depending on the material. Also useful for storing garden produce and can be used for garaging.

There needs to be some way of making sure that ground water pressure does not force water into the structure. If the water table is constantly low (below the lowest part of the basement floor) then a French drain may be sufficient. The French drain, as it is known, is made by placing a layer (about 300mm wide) of gravel or clean hardcore around the walls of a basement with a land drain at the bottom. The point is that this does not prevent moisture encroaching into the basement walls but it does stop water pressure building up and forcing water in. If there is likely to be a problem with damp then the walls and floor can be lined with cavity drain membranes or special types of waterproof concrete can be used.

Existing basements

Often the problem with existing basements is dampness in the walls and floor (and maybe from a vaulted ceiling). The way this is handled depends on how serious the damp is and what the space is to be used for. If the area is subject to wet rather than merely damp (ie. standing water or drips from the ceiling or running walls) then not only will the surfaces need totally lining with a special type of heavy grade plastic liner or stainless steel liner but will also require a perimeter drain in the floor with a sump pump to remove the water.

If it is simply a matter of damp surfaces which never become wet then it may be possible to simply line them with a damp proof membrane and some type of insulation and surface board or finish.

First you must establish whether the basement area is damp or wet (or ever gets wet). These are very different situations because damp can be covered over with a damp proof membrane (DPM) whereas if water ever drips or runs down the walls or there is standing water on the floor then this must be dealt with by leading the water down behind a studded water proof membrane to a drain and pump in the floor. If you are new to the house try to find out if there has ever been flooding or standing water, possibly in neighbouring house basements.

Secondly you need to decide whether you want an unheated storage area with basic functional surfaces or whether it is to be a heated habitable room.

Damp walls and floor for utility/storage/parking use where there will be no heating

This provides no insulation.

 

Insulating basements

Damp walls and floor for habitable use where there will be heating

There are various thicknesses of expanded polystyrene boards and phenolic boards bonded to plasterboard designed for dry lining walls.

Wet walls and floor for utility/storage/parking

If the walls and floor are wet rather than damp then it is possible to use a system of high density polyethylene (HDPE) cavity drain membranes combined with a perimeter floor drain and pump. In this way water leaking out of the surfaces is able to find its way between the membrane studs till it reaches a drain at the edge of the floor. It is then led round to a sump pump which pumps it away to an external drain.

Triton Chemical Manufacturing Co. Ltd. have good detailed information on their web site about how this works. It is possible to plaster or render directly onto the membrane or to fix timber studs.

Wet walls and floor for habitable use

This is similar to above but you will need to add a layer of insulation to bring it up to part L of the Building Regulations. The thickness you add may depend on quite complicated SAP calculations. Probably the best type of insulation is closed cell expanded polystyrene because this is not affected in case any moisture might form due to condensation. The insulation should be faced with a dry lining board.

Building regulations

Structure

The Building Regulations part A covers the structure of a building. This Approved Document goes into a lot of detail for traditional masonry buildings but almost none for timber frame, steel frame, earth building SIPs etc. For these you will need to consult a structural engineer (while SIPs structures are usually handled by the manufacturer)

Fire safety

With most forms of construction there will be implications concerning fire safety. These are covered in the Building Regulations and you can see examples of how to conform with these in Part B (Fire Safety)

 

1 comment to Basements

  • Terry

    The question which springs to mind here is how the potential self-builder decides which option is most appropriate for their needs? For example, how will they know if the water pressure is low or high?

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