Extension plans and drawings

Extension plans and drawings turn an idea into something a council, a building control body and a builder can work from. We start with a measured survey of your house, sketch layout options with you, then produce the drawings needed for planning and for building regulations.

You can use our drawings with our build team or on their own. Either way, the design stage is priced in writing before it starts, so you know exactly what you are paying for.

What is included

• Measured survey of the house and garden
• Two or three layout options to compare
• Planning drawings: existing and proposed plans and elevations, site and location plans
• Building regulations drawings and specification
• Structural calculations from an engineer (full pack)
• 3D views to check the look and the light (full pack)

Who it suits

• Homeowners at the very start of a project
• Anyone who wants fixed designs before getting build prices
• Projects that need a planning application or other approval

Design advice

The most expensive changes are the ones made after the steel is ordered. A good design stage settles layout, heights, glazing and services on paper, so the build price is firm.

How much does it cost?

National guide prices including VAT at 20%. Your area page shows prices adjusted for your region.

Planning rules across the UK

England

In England the main routes are permitted development (ideally confirmed with a lawful development certificate, £274), larger home extension prior approval (£249, 42 days) and a householder planning application (£548, normally 8 weeks), with council fees as set from 1 April 2026.

Wales

In Wales the routes are permitted development (a lawful development certificate is available), or a householder planning application to the council. Wales has no prior approval scheme for larger rear extensions, and fees are set by the Welsh Government.

Scotland

In Scotland the questions are whether the extension falls within householder permitted development (Classes 1A to 1D) or needs planning permission from the council, and the building warrant, which is required before construction begins and is followed by a completion certificate.

Northern Ireland

In Northern Ireland we check the permitted development limits for your house type and, where needed, apply to your council for planning permission, then submit full plans or a building notice to council building control.

Building regulations and neighbours

Building regulations approval is separate from planning. In England you can use the council's building control team or a registered building control approver; a full plans application gets the drawings checked before work starts, and the inspector signs the work off with a completion certificate.

In England and Wales, if the work involves a shared wall, building on the boundary, or digging foundations within 3 m (sometimes 6 m) of a neighbour's building, the Party Wall etc. Act 1996 applies and notice must be served before work starts: two months for work to a party wall, one month for new walls on the boundary and for excavations. Scotland and Northern Ireland have no Party Wall Act.

Questions about extension plans and drawings