House Extensions Hatfield
Single storey rear and double storey extensions in Hatfield, planning, structure and build under one contract.
- Rated 4.9 from 31 reviews on MyBuilder
- Guide from £40,000 (London-derived)
- Free site survey, itemised quote
An extension involves two approvals that run separately: planning, decided by Welwyn Hatfield Borough Council, and building regulations. GS Renovation builds the extension, appoints the structural engineer for the foundations and beams, and coordinates the building control application and inspections. We are fully insured, and quotations are free and carry no obligation.
For Hatfield, on London-derived ranges a single-storey rear extension typically starts from £40,000, or £2,000 to £2,800 per m²; Hertfordshire work generally runs below that. GS Renovation Ltd, a building contractor based in Potters Bar, does the work in Hatfield: the structural engineer we appoint designs the structure, we build it, and building control signs it off.
Price guide
| Work | Indicative range |
|---|---|
| Single-storey rear extension | from £40,000 |
| Rear extension, per m² | £2,000 to £2,800 |
| Side return, per m² | £2,400 to £3,200 |
| Wraparound, per m² | £2,400 to £3,200 |
| Double storey, per m² | £1,800 to £2,600 |
| Basement extension | see the basement page |
Indicative London ranges (Architecture for London, Resi, MyBuilder and Checkatrade, 2026), not a quotation. Hertfordshire work generally runs below the London figures; your price follows a site visit. Prices checked September 2026. Full breakdown: Extension Costs & Planning.
Quick estimate for Hatfield
Hatfield range: choose above
The authority and the plan your application is decided under
Welwyn Hatfield Borough Council is the local planning authority for Hatfield and decides householder planning applications in the town. The Welwyn Hatfield Local Plan 2016 to 2036 was adopted at a meeting of the council on 12 October 2023, and it is the plan a householder application is assessed against.
The council is also preparing a new local plan running to 2043. Its Draft Local Plan consultation ran from 12 February to 26 March 2026 under Regulation 18, and a Regulation 19 stage will follow before examination. The council names no neighbourhood plan covering Hatfield, so there is no further tier of local policy over the top.
Housing in Hatfield
By the valuation list's count, Hatfield holds about 14,820 homes, 63% houses and 37% flats; by age, 3% were built before 1919, 9% between the wars and 88% since 1945. A rear extension on a terrace in Hatfield digs foundations close to both neighbours, so notices to both are normal, and 41% of homes here are terraced.
Where permitted development is restricted
Welwyn Hatfield Borough Council lists Estate Management Scheme areas and high density housing estates among the places where permitted development rights are more restricted. In a conservation area the council states that permission is needed for raising the ridge of the roof, installing dormer windows, installing cladding and constructing extensions. In practice that catches side extensions and two storey rear extensions, while a single storey rear extension within the permitted development limits can still go ahead unless an Article 4 direction removes it.
Trees and heritage settings add their own steps. Owners must notify the council six weeks before carrying out certain works to trees in a conservation area. The park and garden at Hatfield House is on the Register of Parks and Gardens at Grade I under entry 1000343, and registered parks and gardens are heritage assets, so setting can be a consideration for work close by.
The ground your foundations will sit in
The British Geological Survey maps the bedrock beneath central Hatfield as Lewes Nodular Chalk Formation and Seaford Chalk Formation, undifferentiated. Over central Hatfield and parts of the Old Hatfield area, the superficial deposit is mapped as Kesgrave Catchment Subgroup sand and gravel, which the survey describes as cross-bedded and massive, moderately sorted sand and gravel.
South Hatfield is different again. Lambeth Group, a sedimentary bedrock of clay, silt and sand, is mapped beneath much of it rather than chalk, chalk returns a short distance to the east, and much of that ground carries no superficial deposit. Hertfordshire Building Control names foundations as one of the items its inspectors examine on site, and the depth and design come from the engineer.
Getting an early read from the council
Welwyn Hatfield Borough Council runs duty planning appointments. Face to face appointments are held at its Campus East office in Welwyn Garden City from 10am to 12pm on a Wednesday, and telephone appointments run from 10am to 12pm on Monday, Wednesday and Friday. Slots are capped at one 15 minute slot, so take one specific question rather than an open one.
It helps to know what you are extending. At the 2021 census, 11,254 households in Welwyn Hatfield, or 24.4 per cent, were semi-detached, and 9,217, or 19.9 per cent, were detached. The form of the house sets whether a rear, side or wrap around extension is available at all.
Kitchen extensions in Hatfield
65% of the houses in Hatfield are terraced. On a terrace the kitchen extension is built out from the back, into the side return where the house has one or across the full rear width, and a steel beam takes the old back wall so the kitchen and the new room become one space. The fit-out is priced on its own page, kitchen renovation in Hatfield; the build figures are in the table above.
Side return extensions in Hatfield
Side returns belong to Victorian and Edwardian terraces, and only 3% of homes in Hatfield predate 1919, so they are the exception here; most extensions run across the full rear width instead. Our side return extension page covers the build in detail, with build rates of £2,400 to £3,200 per m².
Double storey extensions in Hatfield
Under permitted development a two-storey rear extension can go no more than 3 metres beyond the original rear wall and must stay at least 7 metres from the rear boundary, and in a conservation area it is not permitted development at all. Many gardens are too short for the 7 metre rule, so a double storey extension in Hatfield often needs planning permission from Welwyn Hatfield Borough Council. On the 41% of homes that are terraced, the neighbours' windows usually decide the depth. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Drainage diversion and build-over agreements with the water authority
- Drawings and the structural engineer's design coordinated for you
- Trial holes to set foundation depth near drains and trees
VOA Council Tax stock of properties, March 2025, for Hatfield Town, Hatfield North & West, Hatfield East and Hatfield South. Counts rounded by the VOA.
The GS Renovation Difference in Hatfield
The variable that catches extensions here is the ground. Chalk, sand and gravel, glacial till and Lambeth Group clay are all mapped within the town, so a foundation design that suited one street is not evidence for the next. We appoint the structural engineer, build the foundations to the calculations, and have them inspected before they are covered, because that is one of the items Hertfordshire Building Control examines. Applications and inspections are coordinated, and we are fully insured.
- Permitted development checked before you pay for a planning application
- Insulation and thermal detailing to current regulations
- Itemised pricing, so you can see what every stage costs
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
George is a very hard working builder, and has done a fantastic job on replacing my Bathroom. His attention to detail was great and I wouldn't…
Punctual, worked hard, and did exactly what he was asked and what he said he would do. Overall, a very high quality job. Will use again.
FAQ
Frequently Asked Questions about House Extensions Hatfield
What is the going rate for house extensions around Hatfield?
House extensions around Hatfield typically costs £2,000 to £2,800 per m² for a rear extension (London-derived), but scope varies more than the market does. Two Hatfield jobs of the same size can be different work, because the width of the opening into the house decides the steel. GS Renovation surveys and prices each on its merits at AL10, with the Hertfordshire Building Control fee shown separately.
What does alluvium in the valley north east of Hatfield mean for extension foundations?
The mapped superficial deposit in that valley is alluvium of clay, silt, sand and gravel, which is not what is mapped across the rest of the town. Alluvium is laid down by water and can vary within a short distance, so trial holes on your plot settle the depth rather than the map does. What the mapping gives the structural engineer is a reason to expect variation and a place to start digging.
Are the drains for an extension inspected as well as the foundations?
Yes. Hertfordshire Building Control names drainage as one of the items its inspectors examine on site. An extension can cross an existing run, add a new connection or change falls, and the moment for that inspection is while the pipework is laid and still open. Building control for Welwyn Hatfield is delivered by Hertfordshire Building Control, which is owned by eight local authorities including the borough council, so both items go through the same body.
Can a flat in Hatfield be extended under permitted development?
No. Welwyn Hatfield Borough Council states that permitted development rights apply to houses and do not apply to flats or maisonettes, so an application is needed. An Article 4 Direction confirmed in June 2022 also removes the right to build additional storeys onto existing blocks of flats in Hatfield, and the Secretary of State modified that direction's boundary in October 2022. Check the boundary as well as the direction for a given block.
Do the swallow holes in the local chalk affect foundation design?
The engineer decides that from the site investigation rather than from the reputation of the geology. The Water End Swallow Holes at Welham Green, in the same borough south of Hatfield, were notified as a Site of Special Scientific Interest in 1969, and Natural England maps the site at 11.12 hectares. There, jointing and solution processes have enlarged cracks in the chalk into channels which eventually collapse. That is a designated site, not a description of your garden.
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