A bigger kitchen in a new extension

Many people extend at the back of the house to give the kitchen more room.

A kitchen brings water, waste, heat and power into the new space. These notes take each one in turn, so you can plan for it early.

These notes cover the kitchen side of the project in England. Most extensions need building regulations approval, and a new kitchen in a room that never had one is likely to need it too. The rules in Wales may differ.

Planning the drains for the sink and dishwasher

A drain usually serves one property. A sewer serves more than one. Public sewers belong to the sewerage company, and its address is on your sewerage bill.

If you plan to build over or near a public sewer, you need written agreement from the sewerage company. Talk to them at the earliest planning stage.

The sewerage company or the council will let you look at maps of public sewers free of charge. Private drains are not usually mapped. A drain under the new floor may need moving or protecting, which adds to the cost.

The drain you connect to generally needs to sit at least 0.8 metres below the ground floor level. If it is shallower, ask a builder, architect or drainage engineer.

Ventilating the new kitchen

A new kitchen needs extract ventilation. It reduces condensation and removes smells.

The room also needs an opening window for a quick change of air. A window that opens between 15 and 30 degrees should have an opening area of at least a tenth of the floor area. A window that opens wider needs at least a twentieth.

Background ventilation, such as trickle vents in the window frames, is usually needed as well. Your building control body can agree a different approach.

Opening up the back wall

Once the extension is weatherproof, the builder usually makes an opening through the old back wall. A wider opening needs new beams to hold up the wall above.

Each beam normally rests at least 150 millimetres onto the wall at each end. The wall under it may need a concrete pad to spread the load. A steel beam should normally be protected so that it resists fire for at least 30 minutes, most often with layers of plasterboard.

Power and lighting

A new circuit for a cooker counts as notifiable electrical work. So does any other complete new circuit.

An electrician registered with a competent person scheme can self-certify the work. Otherwise the work has to be inspected by a building control body, or in England by a registered third-party certifier. They must be told before work starts. In Wales, kitchens are a special location, so even small changes to a circuit there are notifiable.

New fixed lighting in an extension also has to be energy efficient.

Moving the cooker or the boiler

Anyone employed to work on gas appliances in a home must be on the Gas Safe Register. They must also be competent in that type of gas work.

The engineer's ID card lists what they are qualified to do. You can check it with Gas Safe Register before the work starts.

Keeping the paperwork

Keep every certificate from building control, the electrician and the gas engineer. They are the certificates of compliance you may need when you come to sell your home.