Welwyn Garden City over-garage extensions, designed and built
Thinking about an over-garage extension for your Welwyn Garden City home? Start with a free site visit: we measure up, check what the council will allow and give you honest guide figures on the day.
- Guide price in Welwyn Garden CityFrom £25,000 inc VAT
- PlanningHouseholder application needed
- Build time12–18 weeks on site
- Postcode districtsAL6, AL7, AL8, AL10
Extensions in and around Welwyn Garden City
Across AL6, AL7, AL8, AL10, we can visit, measure and advise. We also work in nearby Hatfield (3 miles), Hertford (6 miles), St Albans (6 miles), Harpenden (6 miles).
The East of England mixes market-town terraces, inter-war semis and modern estates. Clay soils are common in parts of the region, which can affect foundation design.
Guide prices for Welwyn Garden City
Prices below are for Welwyn Garden City, using the East of England factor of ×1.06. They are guide ranges including VAT for the build only, not a quote.
Typical rates in Welwyn Garden City: £1,910 to £3,600 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Over a single garage 12 m² | £25,000 – £31,500 | £26,500 – £34,500 | £34,000 – £43,500 |
| Over a large single garage 16 m² | £30,500 – £37,500 | £35,500 – £46,000 | £45,500 – £58,000 |
| Over a double garage 24 m² | £45,500 – £56,000 | £53,000 – £69,000 | £68,500 – £86,500 |
Try the guide-price tool to see a range for your own size and finish.
Will the council need to approve it?
In England any side extension over one storey, including a room built over a side garage, needs a householder planning application. The fee is £548 from 1 April 2026 and councils aim to decide within 8 weeks.
Before any drawing is finalised we check whether the house is listed, in a conservation area or subject to an Article 4 direction.
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).
What we take care of
- Strengthening or rebuilding the garage walls if needed
- Opening into the existing first floor
- Design and householder planning application
- Insulation, electrics, heating and finish
Fitting the new room to the existing landing is the planning puzzle inside the house. We design the connection first, then the roof, so the extension does not end up with awkward steps or a corridor through a bedroom.
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
A designer visits, takes measurements and photos, and discusses layouts, budget and timing with you.
Design and approvals
We produce the drawings and structural design, and manage the approvals so they are in place before work starts.
Fixed written price
You receive a written, itemised price and programme. Nothing starts until you are happy with it.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Questions people ask about over-garage extensions
Do I need building regulations approval in Welwyn Garden City?
Yes. Almost every extension needs it, whatever the planning route. We prepare the drawings and book the inspections.
Can I see a price before committing to anything?
Yes. The guide prices on this page are adjusted for Welwyn Garden City, and the guide-price tool gives a range for your own size. After the survey you get a written price before anything is agreed.
Do you cover all of Welwyn Garden City?
Yes. We cover Welwyn Garden City and the surrounding parts of Hertfordshire. Site visits are free and there is no obligation.
Does building over a garage need planning permission?
In England and the rest of the UK, adding a storey over a side garage almost always needs a planning application, because two-storey side extensions are outside permitted development.
Can my garage take the weight of a room on top?
Some can and some cannot. Many garages have a single-skin wall or shallow foundations. Our structural engineer checks this before we give a fixed price.
Book a free site visit in Welwyn Garden City
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.