House Extensions Hitchin
Single storey rear and double storey extensions in Hitchin, 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 is a planning job and a building job, and in Hitchin the planning half needs answering first. We coordinate the design, appoint the structural engineer, make the building control application and build the work. We do not produce structural calculations, and we are not architects or surveyors. This page sets out what governs an extension in Hitchin.
For Hitchin, 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 Hitchin: 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 Hitchin
Hitchin range: choose above
In the Hitchin Conservation Area an extension is not permitted development
The Article 4 direction covering the Hitchin Conservation Area removes permitted development rights for the enlargement, improvement or other alteration of a dwellinghouse. It was made on 9 October 2012. North Hertfordshire has only two Article 4 directions in the entire district, and this is one of them. The other covers Stockens Green Conservation Area, so this is not a district wide rule you can assume applies to a neighbouring town.
The direction removes seven classes of permitted development in total. Among them are the provision of hard surfacing and the erection or construction of a porch where the exterior fronts a highway. It also covers the erection of gates, walls and fences fronting a highway, and painting of the exterior of a building fronting a highway. A driveway and a porch are planning matters inside that area. We confirm the designation for your address before a scheme is drawn.
Housing in Hitchin
Of the 16,130 homes the valuation list records in Hitchin, 14% were built before 1919, 16% between the wars and 69% since 1945; 30% are flats and 70% are houses. A rear extension on a semi in Hitchin digs beside the attached neighbour, so one party wall notice is usual, and 28% of homes here are semi-detached.
Your extension is judged against a recent local plan and a new design code
The North Hertfordshire Local Plan 2011 to 2031 was adopted on 8 November 2022 and forms part of the statutory development plan against which Hitchin applications are determined. It sits alongside the adopted Hertfordshire Minerals Local Plan and Waste Local Plan.
The North Herts Design Code Supplementary Planning Document was adopted by the council on 16 June 2026. It supports Local Plan policies SP9 and D1, and sets clear, written and illustrated design requirements. For a single storey kitchen extension at the back of a Hitchin house, the questions are practical ones: whether it sits within the permitted development limits outside the Hitchin Conservation Area or needs a full application inside it, and what steel the engineer sizes where the old rear wall opens into the new kitchen. We read the code against your scheme before submission rather than after a refusal.
What is under an extension depends on which part of Hitchin it is in
The British Geological Survey maps the bedrock beneath Hitchin town centre as the Zig Zag Chalk Formation, part of the Grey Chalk Subgroup. Over that chalk in the town centre it maps glaciofluvial deposits of Mid Pleistocene sand and gravel. Chalk and a sand and gravel cover are not the same foundation problem, and the depth of the change is what the foundation design turns on.
In the Hitchin Hill area of south Hitchin the survey also maps artificial ground. Worked Ground is mapped at the north end of Hitchin Hill and over a broad area to its west, towards Charlton, and Infilled Ground is mapped to its east. The artificial ground layer is blank along much of the Hitchin Hill road frontage itself, so it cannot be assumed for any one address. That is an argument for a trial hole rather than a rule of thumb.
Six Hitchin streets sit inside an Environment Agency flood warning area
The Environment Agency flood warning area with notation 052FWFIVHG covers Woolgrove Road, Green Lane, Purwell Lane, Brook View, Ninesprings Way and Oakfield Avenue in Hitchin. It is named Ash Brook, Ippollitts Brook and River Purwell at Hitchin, Ashbrook, Little Wymondley and Graveley.
If your address is on that list, floor levels, the ground floor build up and the drainage strategy belong in the planning case rather than in a later conversation on site. We flag it at survey and get it into the design. Applications to Hertfordshire Building Control can be made direct or through the Planning Portal, and its building control telephone number is 01438 879990.
Kitchen extensions in Hitchin
61% of the houses in Hitchin 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 Hitchin; the build figures are in the table above.
Side return extensions in Hitchin
Side returns belong to Victorian and Edwardian terraces, and only 14% of homes in Hitchin 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 Hitchin
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 Hitchin often needs planning permission from North Hertfordshire District Council. With 43% 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
- Full fit-out, finishing and making good
- Bi-fold, sliding and French door openings to the garden
VOA Council Tax stock of properties, March 2025, for Hitchin Town & West, Hitchin Bearton, Hitchin Walsworth and Hitchin Highbury. Counts rounded by the VOA.
Why Choose GS Renovation in Hitchin
An extension in Hitchin turns on which conservation area, if any, covers the address, because the Article 4 direction over the Hitchin Conservation Area takes away the permitted development route that would otherwise apply. We establish that first, then work back through the adopted plan and the design code to a scheme that can actually be consented. From there we appoint the structural engineer, coordinate the building control application and inspections with Hertfordshire Building Control, and build the work. As a contractor we carry the ground investigation, the shell, the roof and the finish, so responsibility does not change hands halfway. GS Renovation Ltd is fully insured and registered in England, company number 14611254.
- Rated 4.9 from 31 reviews on MyBuilder
- Programme planned around party wall notice periods before excavation near a neighbour
- Weathertight shell reached before the fit-out begins
Built a new extension at rear of property. Laid foundations, drainage, raised floor, new roof and completed all fixtures and interior decoration…
Very friendly and I am very pleased with the work he has done, also very clean worker and enthusiastic about his work. Can not fault this company!!!!…
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 Hitchin
How much should house extensions in Hitchin cost?
Expect house extensions at a Hitchin address to cost £2,000 to £2,800 per m² for a rear extension (London-derived), with the property rather than the postcode deciding the figure. At the SG5 survey GS Renovation confirms the detail that matters most, because the depth of neighbouring Hitchin foundations decides how deep the new footings go. Labour, materials and the Hertfordshire Building Control fee are then itemised, so another Hitchin quotation can be compared line by line.
What happens to a drain that runs under where the extension will go?
It is diverted, or the extension is built over it with the right protection, and that is decided before the foundations are set out. Hertfordshire Building Control gives sanitation as part of its remit, and the water authority's build over agreement is a further consent, separate from planning and from building control. A shared drain also serves other houses, so it cannot be blocked or reduced. We locate every run and chamber at survey.
Does a Hitchin address outside the Environment Agency flood warning area still need drainage thought about?
Yes. That warning area, notation 052FWFIVHG, covers six named streets and exists to issue warnings, not to map every risk. The River Hiz runs through the town centre and is culverted in places, and it joins the River Purwell at Grove Mill and the River Oughton near Ickleford. Surface water and a culverted watercourse behave differently from a river in flood. We check the drainage route and the levels for your address at survey.
A neighbour extended without an application before 2012. Does that set a precedent?
No, and the date is the reason. The Article 4 direction covering the Hitchin Conservation Area was made on 9 October 2012, and it took away the permitted development route for enlarging a house inside that area. Work carried out earlier could rely on rights that no longer exist there. Nor is a house outside that conservation area a guide, because the direction reaches only the area it covers. We confirm what applies to your address now.
Do extension foundations at Westmill need to go deeper than elsewhere in Hitchin?
They can, because the mapped ground there is different. At the Westmill estate the British Geological Survey maps Gault Formation mudstone as the bedrock, beneath glaciofluvial sand and gravel. The BGS Lexicon describes the Gault as pale to dark grey or blue grey clay or mudstone, glauconitic in part, with a sandy base. Clay shrinks and swells with moisture, and nearby trees add to that. Depth is set by the engineer from a trial hole, not from the map.
Is a detached garden room caught by the Article 4 direction?
The direction withdraws seven classes of permitted development, and a detached outbuilding is not among the seven. Those classes cover enlarging, improving or otherwise altering a house, altering its roof, chimneys, flues and soil and vent pipes, hard surfacing, and gates, walls, fences, a porch or exterior painting where they front a highway. Conservation area status and the national size limits still apply, so we put the actual building to North Herts Council first.
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