What do extension plans include?

Extension plans are the drawings that show what you want to build and how it joins your house. For a typical home they include a location plan, a block plan placing the extension against your boundaries, and floor plans and elevations of the house as it is now and as it would be afterwards. Sections through the building are added when levels or structure matter.

The same drawings tend to do several jobs. One set supports a planning application. A more detailed set is needed for Building Regulations. Your builder will also want drawings to price from, so the more complete they are, the fewer surprises later.

Do I need planning permission for an extension?

Not always. Many single-storey rear extensions to houses, and some two-storey ones, can be built under permitted development, which gives national consent for certain work without a planning application. The limits cover depth, height, distance from the boundary and the materials used, and the government's technical guidance on householder permitted development sets them out with diagrams.

If your plans go beyond those limits, you apply to your local council's planning department, and the council decides. A designer can prepare the scheme and the application, but nobody can promise the outcome.

What can take permitted development away?

a flat or maisonette, which has no householder permitted development rights
an Article 4 direction made by the council for a street or an area
a condition attached to the original planning permission, which is common on newer estates
a conservation area, where side extensions and rear extensions of more than one storey are not permitted development
a listed building, which needs listed building consent for changes that affect its character, whatever the planning position

Is there a way to get certainty first?

Yes. You can ask the council for a lawful development certificate, which confirms in writing that proposed work is lawful as permitted development. It is optional, but it is useful if a neighbour questions the work, and a buyer's solicitor may later be glad to see it.

What about Building Regulations?

They are separate from planning and apply to most extensions even when no planning permission is needed. They cover structure, foundations, insulation, drainage, ventilation, fire safety and electrics.

There are two routes. With a full plans application, drawings are checked and approved before work begins. With a building notice, you tell building control you are starting and the work is inspected as it goes, without advance approval of drawings. Both are council building control routes. You can use a registered building control approver instead, a private alternative to the council, who checks the work after an initial notice is given. The gov.uk guide on how to apply for approval compares the options. At the end, keep the completion certificate, because a buyer's solicitor will ask for it.

Will I need to tell my neighbours?

You may have to. Under the Party Wall etc. Act 1996, a notice is required if you build on or astride the boundary, cut into a shared wall, or dig foundations close to a neighbour's building. The notice periods are usually one or two months depending on the work. Your neighbour can agree, or the two of you can appoint surveyors to settle the terms.

This is a legal process of its own. Planning permission does not replace it.

What should I think about before the drawings start?

what is not working about the house now, and how you want to use the new space
drains and manholes in the garden, since building over or near a public sewer needs the water company's agreement
trees, which may be protected by a preservation order or a conservation area
how the extension will look from the street and from next door
whether a measured survey of the house is needed to start from

What does a designer do, and what is left to others?

An architectural designer develops the scheme and prepares the drawings. Structural calculations usually come from an engineer, and some projects need a surveyor or a drainage specialist as well. Ask what is covered and what is not before you agree anything, and how the fee is set.

What should I put in my enquiry?

the type of extension, such as rear, side or two-storey
your postcode and whether the house is detached, semi-detached, terraced or a flat
whether it is listed or in a conservation area, if you know
any earlier drawings or planning history
whether you want planning drawings, Building Regulations drawings or both

What happens after I send it?

With your consent, we pass your enquiry to a architectural designer, if one covers your postcode. If nobody does, we tell you and your details go nowhere. Talking terms through with the designer is up to you.

Who you will hear from

We pass your enquiry to one local architectural designer, if one covers your postcode. It is never sent to a list of companies. If nobody covers your postcode, we will tell you and will not pass your details on.