Design and build two-storey extensions in Northamptonshire
We handle a design and build project for homeowners across Northamptonshire, from the first visit to the final paperwork.
Northamptonshire at a glance
- Nation
- England
- Price region
- East Midlands
- Postcode areas
- LE, NN
- Towns covered
- 9 listed below, plus surrounding villages
- Site visits
- Free, no obligation
What a design and build project involves
This service suits you if you want one team accountable from the first visit to the completion certificate. We manage the design, approvals and build, and the work is carried out by vetted teams working under S&K. Because the same team designs and builds, costs are checked as the design develops. Every project starts with a free site visit.
Northamptonshire towns we list: Northampton (NN1), Corby (NN17), Kettering (NN14), Wellingborough (NN8), Rushden (NN9) and Daventry (NN11). Every other address in Northamptonshire is covered as well.
Fees
The design stage is priced in writing before it starts, and the build is a fixed price in writing once the design is agreed.
Rules in England
In England, design and build covers the permitted development check or planning application (£548 (or £575 for applications made from 8 December 2026)), building regulations approval from council building control or a registered approver, Party Wall Act notices where needed, and the Building Safety Act dutyholder roles. We programme them so they overlap where possible.
Approval in England: Householder planning application: £548 (or £575 for applications made from 8 December 2026). Lawful development certificate: £274 (about £288 for applications from 8 December 2026). Councils should decide householder applications within 8 weeks of validation.
Building regulations: Building regulations approval (full plans recommended) from the council or a registered building control approver, with a completion certificate at the end.
The Party Wall etc. Act 1996 applies, so notices may be needed for work on or near a shared wall or boundary.
Getting the design right
Cost checking as you design
Because the people drawing the extension also build it, each design option comes with a guide cost. That avoids the common problem of an approved design that turns out to be too expensive once builders price it.
Responsibility for the rules
In England, where more than one contractor is involved, a principal designer and principal contractor must be appointed. On design and build projects we take on these duties, so you are not left holding responsibilities you may not know you had.
How we work in Northamptonshire
Visit and first ideas
One of our team visits your house in Northamptonshire, checks the walls, roof and drains, and sketches out options with you.
Choose the approval route
Some designs fit permitted development, most need a householder application. We decide which applies in England before drawing in detail.
Detail and price
Construction drawings, engineer's calculations and building control sign-off, then a written fixed price for the build.
On site
One project lead runs the job, keeps you updated and arranges inspections at each stage until completion.
Towns we cover in Northamptonshire
Design and build two-storey extensions in Northamptonshire: questions
Do I have to use you for the build if I pay for the design stage?
No. The design stage is priced separately, so you can take the approved drawings to other builders if you choose. Most people who use design and build carry on to the build, because the design has been costed as it developed.
When is the build price fixed?
Once the design is agreed and the drawings, structural calculations and specification are complete. Before that we give guide costs at each stage. The fixed price is set out in writing before work starts, and any changes you ask for after that are priced separately before they are made.
Who builds my extension?
Your extension is built by vetted teams working under S&K, with the project managed by us from design to completion. You have one point of contact throughout, and the same team that prepared the design is responsible for the build.
Neighbouring areas
- Design and build two-storey extensions in Rutland
- Design and build two-storey extensions in Leicestershire
- Design and build two-storey extensions in Bedfordshire
- Design and build two-storey extensions in Warwickshire
All extension services in Northamptonshire · About design and build two-storey extensions
Ready to see what a second storey could do for your home?
Book a free site visit. We'll look at your house, talk through options and explain the approvals you'd need, then price the design stage in writing.