Conversion of basements

What permission is required before you start work?

Before carrying out a basement conversion it is advisable to seek guidance from the Planning department, as planning permission may be required under the Town and Country Planning Acts and from Environmental Health so that they can consider if the proposed accommodation will be adequate.

A Building Regulations application is required for converting an existing basement to habitable use, excavating a new basement or extending an existing basement.

If the proposed works affect a party wall, e.g. if beams are to bear onto a party wall, the wall is to be extended, altered, underpinned or if excavations are to be carried out near to a party wall, the owners and leaseholders of both the building within which the proposed basement works are to take place and those of adjoining properties must be informed.

The relevant legislation is the Party Wall etc Act 1996.

Guidance notes on the Act are available from DCLG Free Literature, PO Box 236, Wetherby, L23 7NB,or they can be accessed on the internet from the website of the Department of Communities and Local Government.

The Local Authority does not have a role in the implementation of the provisions of the Party Wall etc Act 1996.

Works should not start unless all necessary approvals have been received.

What is the best way of submitting a Building Regulations application?

Basement conversions can encounter a multitude of problems, which could mean that the conversion fails to satisfy the minimum standards set out in Building Regulations and that it does not satisfy its purpose. For this reason, this Borough advises that applications for basements conversions are submitted under the “full plans” procedure.

Where the basement is to be used as a workplace, a full plans application is required.

When a full plans application is deposited, a Building Control Surveyor formally checks the drawings and details submitted. Any deficiencies and potential problems should be resolved before the application is approved. Drawings must accurately represent the existing building, its construction, internal layout, the proposed works and layout.

What are the more common pit-falls with basement conversions?

If one is considering doing a basement conversion, there are a number of points one should consider in particular:

Tanking (waterproofing)

Walls and floors below external ground level and the junctions between them should be provided with a waterproofing system. This is to prevent ground moisture reaching the internal surface of the wall or upper surface of the floor, to maintain satisfactory environmental conditions within the basement for the intended use. Consideration should be given also to determining the position of the water table; whether it is high, low or varies significantly throughout the year.

There are several different ways in which basement walls and floors can be waterproofed. Whatever method is used, it should be appropriate for resisting ground water pressure and should have British Board of Agreement (BBA) or similar independent technical accreditation.

One should bear in mind that good attention to detail and good workmanship are important for the tanking to be successful.

Structure

The existing walls may have to be underpinned and floor level reduced in order to achieve a satisfactory floor to ceiling height. Existing first floor joists may also have to be supported, such as by a steel beam or beams.

It is therefore advisable to seek guidance from a suitably qualified Structural Engineer to undertake the structural design of any underpinning and structural alterations, including drawing up a method statement setting out how and in what sequence the proposed works are to be carried out.

It is necessary that the works are designed with safety in mind and carried out in a safe manner and workmanlike manner.

Reference may be to Approved Document A of the Building Regulations, which makes recommendations for structural elements.

Means of escape in case of fire

In dwellings, basements will usually have a single stairway. In the event of a fire the stairway maybe blocked by smoke from the basement or ground floor storey.

If the basement is to be used for habitable purposes, an external door or window suitable for egress should be provided. Alternatively, a protected stairway leading from the basement to a final exit may be provided.

Means of escape provisions for workplaces are more stringent than those necessary for domestic use and a suitable alternative means of escape is normally required.

Windows provided for emergency egress purposes should have an openable area of not less than 0.33m2 and at they should be at least 450mm high and 450 wide. A self-closing fire door (FD30) should be provided between the basement and the rest of the house. Mains powered interlinked smoke detectors should also be provided in the basement, ground floor hallway and first floor landing.

If the door from a single basement room opens into a room on the ground floor, for example a kitchen, there should be two fire doors at the top of the stair leading in opposite directions. The exit route should be protected by a fire resisting construction.

If the house has 3 storeys before converting the basement, self-closing fire doors are required to the basement and to the other rooms which open onto the stairs at all levels. Mains operated and interlinked smoke detectors should be provided at all levels.

Any services of more than 40mm in diameter which pass through an element providing fire separation, should have the same fire resistance as the fire-resisting compartment it penetrates.

Works to basements that may be used as a workplace require consultation with the London Fire Brigade.

Ground floor fire resistance

The ground floor should achieve at least ½ hours fire resistance, unless it is a compartment floor, in which case it should achieve at least an hours fire resistance.

There should be at least 100mm insulation between the ground floor joists and 2 layers of 12.7mm plasterboard used with joints staggered.

Ventilation

Basements used for habitable or workplace use should have adequate natural ventilation. Rapid ventilation, through openings of not less than 1/20th of the floor area, with secure controllable background ventilation, should be provided.

An appropriately designed mechanical ventilation system may be used as an alternative for workplace uses.

Note: Ventilation should be maintained to any adjacent timber ground floor, for the prevention of condensation and any consequent risk of timber decay.

Stairs

Stairs to the basement should have a pitch of not more than 42 degrees and have a headroom of not less than 2.0 metres, with suitable handrails and non-climbable balustrading with gap of less that 100mm between spindles.

Thermal insulation

Insulation should be provided in external walls and floors. The insulation should have a reasonable thickness. The insulation should be compatible with the tanking material.

All new windows and doors should be to current standards, i.e. with a U value of 2.0Wm/2oK or less.

Energy efficient lighting should be fitted to the room.

Electrical installations

New domestic electrical installations must comply with Part P of the Building Regulations and should be installed either by a registered self-certifying electrician or by a competent person who can issue an electrical installation certificate under BS7671.

Notes:
Although this list may cover many common issues, it will not cover all situations. Absolutely precise information cannot be given as individual circumstances vary.

Additional measures may be required to satisfy the provisions of the Building Regulations and other statutory requirements.

Contact us

Building Control
Environment and Regeneration
Waltham Forest Council
Sycamore House
Forest Road
London E17 4JF
Tel 020 8496 3000
Email building.control@walthamforest.gov.uk