Annexe extensions in Boston: design, approvals and build
A annexe extension in Boston starts with the right design and the right approval route. We take care of both, then build it with our own project management.
- Guide price in BostonFrom £52,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsPE21
Included in a typical project
- Design for accessibility: level thresholds, wider doors, walk-in shower
- Fire separation and alarms to building regulations
- Planning application describing ancillary use
- Kitchenette, shower room and bedroom finish
Guide prices for Boston
Prices below are for Boston, using the East Midlands factor of ×0.95. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Boston: £1,900 to £3,610 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Studio annexe 25 m² | £52,000 – £65,500 | £57,000 – £71,500 | £71,000 – £90,500 |
| One-bedroom annexe 35 m² | £66,500 – £83,500 | £79,500 – £100,000 | £99,500 – £126,500 |
| Larger annexe 45 m² | £85,500 – £107,000 | £102,500 – £128,500 | £128,000 – £162,500 |
For a figure based on your own dimensions, use our guide-price tool.
Extensions in and around Boston
We cover Boston and the postcode districts PE21. The same team covers Spalding (14 miles), Skegness (19 miles), Grantham (26 miles), Lincoln (27 miles), all within easy reach.
Just over the Cambridgeshire border, Wisbech is about 23 miles away. Homes across the East Midlands often have usable side land or a driveway beside the house, which opens up side and wraparound options.
Planning rules that apply in Boston
In England an annexe that stays part of the household and connects to the house is assessed as an extension, but its size usually takes it beyond permitted development, so a householder application describing the ancillary use is the normal route.
Homes in conservation areas, national parks, National Landscapes (formerly AONBs), the Broads and World Heritage Sites have tighter rules, so we always check the property's status and planning history before design starts.
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.
Applications are decided by the local planning authority (your district, borough or unitary council).
Our process, step by step
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
Our team builds the extension, keeps you updated weekly and finishes with building control sign-off.
Questions people ask about annexe extensions
Do you cover all of Boston?
Yes. We cover Boston and the surrounding parts of Lincolnshire. Site visits are free and there is no obligation.
How long does an annexe extension take to build in Boston?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 10–16 weeks design and approvals.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Boston, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
Can the annexe have its own front door?
Yes, many do, but it should still connect to the main house to stay clearly part of it.
Does an annexe extension need planning permission?
Usually yes, because of its size and the way it will be used. Councils check that it stays ancillary to the main house, so the application must describe the use clearly.
Book a free site visit in Boston
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.