House extensions in East Sheen & South West London

What building an extension involves

Every extension follows the same broad sequence: the design is agreed and approved, the site is set up and the old wall or garden area is cleared, foundations and drainage go in, then the walls, roof and any steel beams follow. Once the structure is weathertight, the electrics, plumbing and heating are run in, the walls are plastered and the space is finished and decorated.

The moment most families notice is when the back wall of the house is opened up. We plan that stage carefully so the house stays secure and weathertight, and we agree with you in advance which rooms will be out of action and for how long.

Timescales depend on size and complexity. As a rough guide, a single-storey rear or side-return extension usually takes around three to four months on site, and larger wraparound or double-storey projects take longer. You receive a written programme for your project before work starts.

Planning permission and permitted development

Many single-storey rear extensions can be built under permitted development, which means they don't need a full planning application, provided they stay within set limits on size, height and materials. Side-return and wraparound extensions, double-storey extensions and homes in conservation areas or with Article 4 directions more often need planning permission. Flats and maisonettes don't have permitted development rights for extensions at all.

The rules are detailed and change from time to time, so check your own house against the current guidance on the Planning Portal. Where a project relies on permitted development, applying for a Lawful Development Certificate gives you written confirmation that it's lawful, which is useful when you come to sell.

Building Regulations and the Party Wall Act

Whether or not planning permission is needed, an extension must comply with the Building Regulations: structure, foundations, fire safety, insulation, ventilation and drainage. A building control inspector checks the work at key stages and issues a completion certificate at the end, which you will need when you sell.

If the work involves a wall shared with a neighbour, or digging foundations close to theirs, the Party Wall etc. Act 1996 usually requires you to serve notice on them before work starts. Allow time for this in your plans. The government's Party Wall guidance explains how the process works.