We earn a commission for products purchased through some links in this article.

Expert advice: planning a side extension

Follow our simple step-by-step guide from concept to completion

kitchen extension
Ben Anders

What to know before you build:

Work out your available budget.
Be realistic. A typical London side extension will start from £125,000 plus VAT, but you will also need to allow for consultant fees and surveys, which typically work out at around 20 per cent on top of the construction cost.

Research and choose an architect
Check their previous work to ensure they fit your aesthetic as well as your budget – and put together a brief detailing what you want to achieve.

Research planning permission.
You may be able to do a small extension under permitted development rules: for side extensions that means that it can be no wider than half the width of the original house and no higher than four metres. Rear extensions must not extend more than three metres beyond the back of the house for an attached property, and four metres for a detached building.However, most new extensions will require permission. Find out more, and apply at planningportal.co.uk/; the application usually costs £172.

extension with window seat
This extension by McLaren Excell, is about adding light and space. The façade is clad in rust-effect Corten steel and the interior joinery is made from grey elm. A generous ledge runs around the inside of the box window, providing a perfect spot to sit and gaze out over your garden. Tip: the box seat is also a great place to sneak in extra storage.
McLaren Excell

Consider party wall issues
A party wall is one shared between neighbours, so if you want to build on, or off, it, you’ll need their permission. You must alert your neighbour of any work taking place on or near a party wall at least two months before work commences – letter templates are available at gov.co.uk. They must then reply within 14 days.

If they agree, perfect, but make sure you have consent in writing. If they do not, you will need to appoint a surveyor (your neighbour can also choose to appoint their own) who will agree the Party Wall Award – a document detailing what work will be done, when, and who will be responsible for all of the costs (including surveyor fees).

wraparound glass doors
Bradley Van Der Straeten has turned this garden door into a dramatic feature that stretches around the corner of the extension. The design has two elements – a bi-folding door on the right and a smaller pane of glass on the left, which can be folded back against the wall.
Bradley Van Der Straeten

Technical designs
Your architect will lead this stage, which normally takes about two months. The detailed technical aspects of the project will be drawn up and given to potential builders.

This can take between eight and 12 months depending on the complexity of the project. Your architect will administer the building contract and inspect the builder’s work.

This article appeared in the September 2016 issue of ELLE Decoration.

Like this article? Sign up to our newsletter to get more articles like this delivered straight to your inbox.


Keep up your spirits and subscribe to ELLE Decoration here, so our magazine is delivered direct to your door.

This content is created and maintained by a third party, and imported onto this page to help users provide their email addresses. You may be able to find more information about this and similar content at piano.io
Advertisement - Continue Reading Below
More From Expert Advice