Single-storey extensions
Where foundations, drains, structural openings and roof junctions usually create the real work.
House extensions across the UK
Plan the Extension Before You Build It
A house extension is much easier to control when the awkward parts are dealt with on paper: where the drains run, what supports the old rear wall, how the roof meets the house and which approvals apply.
Dimensions and finishes matter, but they come after the basic questions about structure, ground, water and access.
Quote requests are provided by MyJobQuote, an independent third-party service.
One useful rule
Do not finalise the room layout until the drains, structural opening and finished floor levels have been checked against the existing house.
Planning permission
How permitted development, previous extensions and local restrictions affect the route.
Building Regulations
Structure, insulation, drainage, fire safety and completion paperwork.
Extension costs
Why floor area alone does not explain the final price.
Party walls
When foundations, boundaries or shared walls may trigger notice in England and Wales.
Choosing a builder
Compare scope, organisation and comparable work rather than headline price.
Before the foundations
Find out what is already in the ground
Rear and side extensions regularly meet drains, shallow old footings, filled ground and tree-influenced soil. A few early checks can prevent the foundation design changing after excavation has started.
Where new meets old
The junctions deserve more attention than the middle
Roof abutments, thresholds, cavity closures and the opening through the old external wall are where several parts of the extension meet. These details can affect leaks, heat loss, cracking and the amount of structural steel required.
Planning is not one UK rule
Check the rules that apply where the house is
England, Wales and Scotland have different detailed permitted-development limits, and Northern Ireland has its own planning system. The Party Wall etc. Act applies in England and Wales, not Scotland or Northern Ireland.
Extension guide library