House Extensions St Albans
Single storey rear and double storey extensions in St Albans, 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
GS Renovation builds house extensions in St Albans, from single storey rear kitchen extensions on post-war semis to side and two storey additions. The planning position here is unusual, because the adopted plan dates from 1994 while a new plan sits at examination. We appoint structural engineers, build to their calculations, and coordinate building control applications and inspections.
For St Albans, 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 St Albans: 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 St Albans
St Albans range: choose above
The adopted plan your extension is judged against dates from 1994
The current adopted Local Plan for St Albans is the District Local Plan Review 1994, adopted on 30 November 1994, and it is one of several documents that together make up the Development Plan for the district. St Albans City and District Council describes it as one of the oldest in the country. That is the council's own description, not ours.
Not all of it still applies. Local Plans expired after 27 September 2007 unless saved, and a Direction made in 2007 saved specified policies of the District Local Plan Review 1994. The council published a saved and deleted policies version in July 2020, so the live policy set is narrower than the original document. Check which version a policy reference comes from before relying on it.
Housing in St Albans
The Council Tax list puts St Albans at about 29,270 homes, 32% flats against 69% houses; 19% went up before 1919, 17% between the wars and 63% after 1945. 27% of homes here are terraced; a rear extension on a terrace in St Albans digs foundations close to both neighbours, so notices to both are normal.
The emerging plan already carries weight in decisions
St Albans City and District Council states that its emerging Local Plan now has significant weight in decision making, with its policies an important material consideration. The new draft Local Plan was submitted to the Planning Inspectorate for independent examination on 29 November 2024 under Regulation 22. A consultation on Main Modifications under Regulation 24 commenced on Monday 13 April 2026.
For a householder extension that means two policy sets are live at once, the saved 1994 policies and the emerging ones. We are a contractor, not a planning consultant and not an architect, so we do not argue your case for you. We build what is consented, appoint the structural engineer, and coordinate the building control side once permission is settled.
Four Article 4 areas where permitted development has been removed
Four heritage Article 4 Direction areas cover parts of St Albans District: Verulam and Fishpool Street, Sopwell Lane and Albert Street, Cunningham Avenue and Childwickbury. The Sopwell Lane and Albert Street Direction, dated 5 July 1990, removes permitted development rights under Part 1 Classes A to H and Part 2 Classes A to F. Part 1 Classes A to H is the part that covers extensions, roof alterations and porches.
The Verulam and Fishpool Street Direction, dated 2 January 1991, removes Part 1 Classes A to H and Part 2 Classes C to F. It is recorded as removing Part 2 Classes C to F only, so it does not remove Part 2 Class A, which covers gates, fences, walls and other means of enclosure. The Sopwell Lane and Albert Street Direction does remove Class A. The two are not identical, and the address decides which applies.
Foundations sit on chalk with sand and gravel over it
BGS 1:50,000 mapping records the bedrock beneath St Albans city centre as the Seaford Chalk Formation, with the superficial deposits above it mapped as the Satwell Gravel Member, sand and gravel within the Kesgrave Catchment Subgroup. Across Fleetville, Marshalswick and The Camp the superficial cover is mapped as Kesgrave Catchment Subgroup sand and gravel, deposits formed by an ancestral River Thames.
Beneath the London Road area of south St Albans, close to Cunningham Avenue, BGS maps River Terrace Deposits of sand and gravel. Sand and gravel over chalk is a different foundation problem from clay, and it changes excavation, trench stability and drainage falls. The structural engineer we appoint specifies the foundation and we build to that specification. On the post-war semis of Marshalswick the usual project is a single storey kitchen extension across the back, with a steel beam where the old rear wall opens into the new room, and the foundation depth is set once trial holes show what the sand and gravel is doing.
Kitchen extensions in St Albans
58% of the houses in St Albans are semi-detached or detached, which usually leaves room for a kitchen extension across the full rear width, with a steel beam over the opening into the house. The fit-out is priced on its own page, kitchen renovation in St Albans; the build figures are in the table above.
Side return extensions in St Albans
Side returns belong to Victorian and Edwardian terraces, and only 19% of homes in St Albans 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 St Albans
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 St Albans often needs planning permission from St Albans City and District Council. With 40% of homes here semi-detached or detached, the side of the house is often an option too. Our double storey extension page explains the build, at £1,800 to £2,600 per m² across both floors.
- Drawings and the structural engineer's design coordinated for you
- Drainage diversion and build-over agreements with the water authority
- Levels, drainage and landscaping made good around the new build
VOA Council Tax stock of properties, March 2025, for all 9 statistical areas in St Albans. Counts rounded by the VOA.
Why Choose GS Renovation in St Albans
An extension in St Albans is argued against a plan adopted in 1994 alongside an emerging plan the council says now carries significant weight, so the consent stage is where the time goes. We build what is consented. We appoint the structural engineer, build to the calculations, and coordinate the building control application and the inspections through to the completion notice. Fully insured, registered in England, company number 14611254, with free no obligation quotations.
- Programme planned around party wall notice periods before excavation near a neighbour
- Rated 4.9 from 31 reviews on MyBuilder
- Weathertight shell reached before the fit-out begins
Reviewed jobs near St Albans
2 MyBuilder reviews from St Albans, with each customer's own job title:
- Downstairs toilet fitting, St Albans, 24 Jan 2018 (1 out of 5)
- Complete new bathroom inc tiling walls & floor, St Albans, 20 Nov 2017 (5 out of 5)
Read all 31 on our reviews page.
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…
The kitchen has been fitted to the high standard. Saaid was polite, professional, tidy, he pays attention to a little details that make huge…
FAQ
Frequently Asked Questions about House Extensions St Albans
How accurate is a house extensions quote for a St Albans house?
Accuracy on a house extensions quote in St Albans comes from surveying, itemising and standing behind the total within £2,000 to £2,800 per m² for a rear extension (London-derived). Quoting low to win a job and correcting it later is the commonest complaint about builders. GS Renovation prices in the order the work runs: the steel into the house is designed before the rear wall comes down. Anything unforeseen is costed before continuing at AL1.
Which stages does building control inspect on an extension?
Eleven are named: commencement, foundations excavated, damp proof course or tanking, oversite, drains laid, floor joists, steelwork, roof carcass, insulation, windows and completion. Which of them apply depends on the design, and a single storey rear addition will not reach all of them. Surveyors carry out site visits Monday to Friday between 10.30am and 2.30pm, so the build programme is planned around that window.
Is a house at the southern edge of St Albans in the Green Belt?
It can be. Green Belt land is recorded on the national planning data register immediately south of the St Albans built up area, around Sopwell and Cottonmill. Where a property sits inside that boundary, an extension is judged on different grounds from the same work further into the city, and the council decides. We are contractors rather than planning consultants, so we flag it before a design is commissioned.
Can solar panels or a heat pump be added while the extension is built?
Not without permission at a Cunningham Avenue address. The Article 4 Direction there, dated 3 November 2014, removes Part 14 Classes A to I, the permitted development rights covering renewable energy equipment such as solar panels and heat pumps. The same Direction removes Part 1 Classes A to H and Part 2 Classes A to C. Elsewhere in the district the position varies by address and the council determines it.
Do the neighbours have to be told before the foundations are dug?
Where the excavation is close to their structure, yes, and the party wall route covers it. Interwar stock brings this up: in the Cottonmill and Sopwell area, 560 of 3,240 dwellings, 17.3 per cent, were built between 1930 and 1939, on plots where the boundary sits near the house. You serve the notice as building owner before digging starts, not once the trench is open. We say when a surveyor is needed.
Does a protected tree in the garden stop a rear extension?
Not on its own, but it shapes the foundation and the way the trench is dug. The national planning data register records 670 tree preservation orders and 544 tree preservation zones for St Albans City and District Council, and consent is needed before a protected tree is pruned or felled. Where a foundation runs inside the root zone, the engineer specifies a deeper or different design at drawing stage.
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