Basements

A well-converted basement or cellar can be an interesting space and a great way of getting extra room in your house but they will involve a high level of scrutiny from your local authority building control team – this is because of significant damp and structural safety issues as well as means of escape in the event of a fire implications. Depending on the size, quality of build and the finish, converting a basement or cellar can increase your property value by 20% or more – local estate agents are probably best placed to advise further.

Straightforward basement or cellar conversions could provide a good return on investment, especially if it is an existing space with no structural changes required. For projects that require excavation and/or underpinning, the costs involved will be significantly higher depending on There has been a significant resurgence in basement and cellar conversions in residential developments over the past few years, particularly in urban areas, where there is limited space to construct above ground extensions.

The location, scale, build quality and specification and other factors that can push up your basement/cellar conversion costs:

• If you have to divert drainage or if the area has a high water table which means you need a pump to be working constantly.
• Your property sits on certain types of ground such as clay, sand, marsh or made-up ground (previously excavated material.)
• The site is difficult to access or has nowhere to store excavated soil.
• There is high demand for parking on your street and you can’t get permission for a skip.

Substantial basement and cellar conversions can be extremely complex projects and a poorly thought-out conversion can even reduce a property’s value, and in some cases compromise the structural integrity of your existing home as well as neighbouring properties. Therefore, like all building projects, it is important to plan your conversion very carefully and get the work carried out by an experienced contractor.

Design issues to consider

When you are thinking about whether your basement or cellar is suitable for conversion you might like to consider:

• Structure: Is there sufficient headroom, bearing in mind that the ceiling and the floor treatments that you will have to install are likely to reduce the available headroom?
• Means of escape: What provision will be required for means of escape in the case of a fire and how does this impact the rest of your property?
• Drainage: Does the space ever flood?
• Access: What is the access like? Is there a place for a staircase?
• Storage: Will you have enough storage space if you convert your basement/cellar?
• Suitability: Is there enough room to provide the accommodation that you require or would you be better extending the property?
• Ventilation: Is there any ventilation to your cellar or could any be provided?

What permissions do I need?

You will almost certainly need planning permission if you are making any structural changes or altering the external appearance of the property, or if the building is listed or in a Conservation Area.

You should also check with your local planning authority whether it requires a Basement Impact Assessment before granting approval. Due to a growing number of concerns from homeowners about potential structural and water damage to their properties, a number of London councils now require the submission of a Basement Impact Assessment during the planning application stage. If you are making structural changes and share a wall with your neighbour, you may also need an agreement under the Party Wall etc. Act 1996. Building regulations on the other hand, are applicable to the conversion of all basements and cellars as well as the construction of new ones.

Building regulations and basements/cellar conversions

Building regulations will apply to structure, thermal insulation, ventilation, drainage, ceiling heights, damp proofing, electrical wiring, water supplies, fire protection and means of escape in the event of a fire.

Structure

If there is not sufficient headroom in your basement/cellar it is sometimes possible to lower the floor but this is not a straightforward procedure. You’ll need to carefully consider if lowering the floor will undermine the house or the neighbour’s house foundations and whether the floor will end up below the water table as this could make the property more vulnerable to flooding – specialist advice is recommended before considering lowering floors.

Damp proofing

As most basements or cellars are set below the ground they tend to suffer from problems with damp. A number of systems are available for damp proofing basement and cellars; most of them will use a waterproof render system known as tanking which forms a continuous damp proof layer across the floor and up the walls. This is generally Wherever a new stair is installed in a basement/cellar conversion, it should be designed in accordance with the following guidance.

• Pitch: The maximum pitch for the stair should not exceed 42 degrees.
• Rise and going: The maximum rise of each tread of a domestic stair should not exceed

220mm and the going should be at least 220mm.

• Headroom: There are no reductions permitted – it is a simple 2m minimum above the pitch line.
• Handrails and balustrades: The stair should be provided with a handrail at least 900mm high and any exposed edges of stairs or landings should be provided with balustrading at least 900mm high. Ballustrades should not allow a 100mm sphere to pass through and should not be climbable. Need to install a new stair? installed by specialist companies who will offer an insurance-backed guarantee for the installation – your local authority building control team will need to approve details of both the system and installer prior to installation.

Some basements and cellars will already have good, stepped access to them. However, whether the existing stairs will provide suitable access to a habitable room is a matter of professional judgment. If there are no steps, or if the existing steps are inadequate, a new stair will need to be installed Careful consideration should be given to the best location for the stair and this will be influenced by a number of factors including the layout of the existing house, the headroom available and whether a secondary means of escape can be provided from the basement/cellar area.

Fire safety

All basement and cellars converted for habitable use will need a suitable escape route in the event of a fire. Often existing light wells/windows can be upgraded to provide a secondary fire escape as well as ventilation. These windows need specialist fire hinges which ensure that it can be fully opened so you can climb up from the light well to ground level in the event of a fire. If you cannot provide a secondary fire escape, the staircase will need to end up in a fire protected hallway with a door direct to outside. When converting your basement or cellar it is a good opportunity to review the fire precautions that are available in your existing home. Mains operated smoke detection significantly improves fire safety in the home and the building regulations require that it should be installed where basements are converted for habitable use.

Drainage

Drainage needs careful consideration at an early stage in any basement/cellar conversion as it can be problematic, especially if you are looking to include a sink, bathroom, shower room or new fixed appliances. New appliances, such as a washing machine, will need to connect to the existing foul drainage system, but these are usually found above the level of the appliances you are looking to install. The solution here is to install a pumped drainage system that macerates the drainage and pumps it to the existing drainage system. You will need suitable routes for pipes to run to a point where they can connect to existing drains.

Ceilings

Adequate ceilings need to be provided as part of your basemen/cellar conversion, primarily for fire, thermal insulation and sound-proofing purposes. Plasterboard is probably the most common material used for ceilings as it offers good fire resistance and flame spread properties. If your basement/ cellar or the room above is to be used as a bedroom you will need to install acoustic quilt for sound proofing within the floor void between the rooms.

Heating

If you are looking to install heating as part of the conversion, extending the existing central heating system is the most effective solution but your plumber heating engineer will need to check that your existing boiler and pump has sufficient capacity to serve any additional radiators.

Ventilation

Any new habitable rooms in the basement/ cellar will need to be ventilated and this can sometimes present a problem for converting basement/cellar conversions. Where natural ventilation through windows is not practical a mechanical ventilation system will need to be installed, but these will need to be approved by your local authority building control team.

Thermal insulation

Your basement/cellar conversion should provide an insulated envelope so that heat loss minimised. As well as insulation, you should consider the efficiency of any services you install. Low energy light fittings should be used where possible and any new heating systems should work to high levels of efficiency and have suitable thermostats and controls. Further information about energy efficient heating systems is available in the chatbot elsewhere

Electrics

It is sometimes possible to extend existing circuits to basement/cellar conversions but often new circuits and a new distribution board will be required. Seek advice from a competent electrician at an early stage to see if your electrical system can be extended.