Downstairs toilet: fitting a cloakroom WC where there was none

A toilet needs a soil pipe that falls steadily to the drains, and the easiest positions are close to an existing soil stack or a manhole. Under-stairs spaces on an outside wall near the kitchen drain are often straightforward. A position in the middle of a house with a solid floor may mean breaking out the floor to lay a new drain, and in a timber floor the pipe has to run between or through joists without weakening them.

Where gravity drainage is impossible, a WC with a macerator and pump can discharge through small-bore pipe. Approved Document G only accepts this where there is also access to a WC that discharges directly to a gravity system, so a macerator toilet can be an additional toilet but never the only one in the house. Macerators also need an electrical supply and occasional maintenance, and they are noisier than a normal toilet.

A new toilet needs extract ventilation. Approved Document F gives a minimum intermittent rate of 6 litres per second for a room with a toilet; a window that opens wide enough for purge ventilation can be used instead where security is not a concern. Under-stairs WCs rarely have a window, so a fan ducted to the outside is usual, and the duct route should be part of the quote.

Approved Document G requires hand washing facilities in the toilet room or in an adjoining space that is the only way into it, and that space must not be used to prepare food. The room with the toilet must be separated by a door from any kitchen or food preparation area. A toilet that opens straight off a kitchen, with no door between the two, does not meet the guidance.

• where the soil pipe runs and how it connects to the drains
• whether a macerator is proposed, and why
• fan position and duct route to the outside
• hand basin size and its water supply
• door position and which way it opens
• lighting and electrical work, and who certifies it
• the Building Regulations route and who submits it

An under-stairs toilet works when there is enough headroom where you stand at the basin and in front of the toilet. The sloping ceiling can sit over the cistern, but not over your head as you stand up. Wall-hung toilets with a concealed cistern and small corner basins help, and a door opening outwards, or a pocket door, often makes a tight room usable.

The stairs above are usually part of the escape route from the upper floors. Cutting into a stair enclosure or removing the underside lining can affect its fire protection, so ask how the fitter will keep the enclosure intact.

The Planning Portal says that providing a bathroom or WC in a room where there was none before is likely to need Building Regulations approval for ventilation, drainage, structure, electrics and fire safety. Planning permission is not normally needed unless it is part of an extension or the house is listed.

In practice, a building notice or full plans application is made to Building Control, and an electrician registered with a competent person scheme can self-certify their part. Keep the completion certificate: buyers' solicitors often ask for it when a downstairs toilet looks recent.

Describe where you would like the toilet, the nearest drain or soil pipe if you know it, and the floor type. Once your phone number and email are confirmed, businesses in your area see the job without your contact details. One of them can buy it, and it is then removed from our list. We email you the business's name, address and phone number before it receives your details. It is free for you, there is no guarantee of a taker, and it is withdrawn after 21 days if unsold. Offrano only checks that buyers are registered businesses, so ask who will handle the Building Control application.