Extension plans and drawings across Thornbury
For Thornbury homeowners we handle extension plans and drawings, with fees agreed in writing before any work starts.
- Guide price in ThornburyFrom £1,200 inc VAT
- PlanningWe find the right route for you
- Timescale2–6 weeks for drawings
- Postcode districtsBS35
When it helps
- Homeowners at the very start of a project
- Projects that need a planning application or other approval
- Anyone who wants fixed designs before getting build prices
What it costs in Thornbury
Guide fees for Thornbury including VAT, using our South West England factor of ×1.02. Council and building control charges are not included.
| Option | What it covers | Guide price |
|---|---|---|
| Essential | Measured survey and planning drawings | £1,200 – £2,250 |
| Standard | Planning drawings plus building regulations drawings | £2,200 – £3,900 |
| Premium | Full pack with structural calculations and 3D visuals | £3,450 – £5,650 |
Try the guide-price tool to see a range for your own size and finish.
Extensions in and around Thornbury
Postcode districts we cover around Thornbury include BS35. Neighbouring towns we cover include Yate (7 miles), Mangotsfield (8 miles), Kingswood (10 miles), Dursley (10 miles).
Portishead, in Somerset, is roughly 12 miles from Thornbury and also on our list. South West homes range from terraced streets in the cities to stone cottages and bungalows in the countryside, and conservation areas are common in historic centres.
Will the council need to approve it?
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.
In a conservation area, national park, National Landscape, the Broads or a World Heritage Site the permitted development limits are tighter (no side or two-storey extensions without an application). Listed homes need listed building consent, and if permitted development rights have been removed, any extension needs an application.
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.
Building over or within 3 m of a public sewer needs the water company's consent, usually through a build-over agreement, before the foundations go in.
Applications are decided by the local planning authority (your district, borough or unitary council).
How the project works
Site visits are free and there is no obligation. Where drawings are needed, the design stage is priced in writing before it starts.
Free site visit
First, a site visit: we look at the house, garden, access and drains and listen to what you need.
Design and approvals
We draw the design, agree it with you and handle planning or permitted development checks and building regulations.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
The build is managed from start to finish, inspected at each stage and signed off on completion.
Questions answered
How long does this take for a Thornbury home?
2–6 weeks for drawings, depending on the council and the complexity of the project.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Thornbury, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
Who do I contract with in Thornbury?
Your contract is with S&K Property Investments and Improvement Ltd, which designs and manages the project and the build teams who carry it out.
Can I use your drawings with another builder?
Yes. Once paid for, the drawings are yours to use for your project.
How much do extension plans cost?
Our design packs range from about £1,200 to £5,650 including VAT, from planning drawings only to a full pack with building regulations drawings, structural calculations and 3D views. Council fees are separate.
Book a free site visit in Thornbury
We will measure up, check the planning position and give you honest guide figures.
- Free, no-obligation site visit
- Planning route checked before you spend on drawings
- Written price once the design is agreed
- Building control sign-off at the end
Prefer to talk? Call 0800 088 6341 or .
Book a free site visit
Tell us a little about the project and we will arrange a time.