Annexe extensions across Welwyn Garden City
Welwyn Garden City homeowners can use us for the whole annexe extension project: survey, design, planning or permitted development checks, building regulations and the build itself.
- Guide price in Welwyn Garden CityFrom £58,000 inc VAT
- PlanningUsually a householder application
- Build time16–24 weeks on site
- Postcode districtsAL6, AL7, AL8, AL10
Planning rules that apply in Welwyn Garden City
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.
The planning position for a specific Welwyn Garden City address depends on its history and any designations, which is why we check it at the first visit.
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).
Annexe extension prices in Welwyn Garden City
Labour and material costs vary across the UK, so for Welwyn Garden City we use our East of England factor (×1.06). The ranges include VAT and exclude design, structural and council fees.
Typical rates in Welwyn Garden City: £2,120 to £4,030 per m² including VAT, depending on specification.
| Size | Essential | Standard | Premium |
|---|---|---|---|
| Studio annexe 25 m² | £58,000 – £73,000 | £63,500 – £79,500 | £79,500 – £101,000 |
| One-bedroom annexe 35 m² | £74,000 – £93,000 | £89,000 – £111,500 | £111,000 – £141,000 |
| Larger annexe 45 m² | £95,000 – £119,500 | £114,000 – £143,500 | £143,000 – £181,500 |
Try the guide-price tool to see a range for your own size and finish.
Local to Welwyn Garden City
Across AL6, AL7, AL8, AL10, we can visit, measure and advise. Neighbouring towns we cover include Hatfield (3 miles), Hertford (6 miles), St Albans (6 miles), Harpenden (6 miles).
Just over the Bedfordshire border, Luton is about 10 miles away. 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.
What is included
- Separate or shared heating and hot water
- Planning application describing ancillary use
- Design for accessibility: level thresholds, wider doors, walk-in shower
- Kitchenette, shower room and bedroom finish
- Fire separation and alarms to building regulations
Accessibility is cheaper to design in than to retrofit. Level access, a 900 mm door width, a level-access shower and space to turn a wheelchair can all be planned into the footprint for little extra cost.
What happens next
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
We confirm the build price in writing, based on the approved drawings and the finishes you have chosen.
Build and sign-off
Work is carried out to the agreed programme, inspected by building control and signed off at the end.
Your questions about an annexe extension in Welwyn Garden City
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.
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.
How long does an annexe extension take to build in Welwyn Garden City?
On site, typically 16 to 24 weeks once approvals are in place. Before that, allow 10–16 weeks design and approvals.
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.
Will an annexe affect council tax?
It can. Some annexes are assessed separately for council tax, with discounts or exemptions in some cases when occupied by a relative. Check with the Valuation Office Agency (England and Wales), your local assessor (Scotland) or Land & Property Services (Northern Ireland).
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.