House Extensions Hemel Hempstead
Single storey rear and double storey extensions in Hemel Hempstead, 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 Hemel Hempstead: single storey rear, side returns, wrap arounds and two storey additions. We appoint the structural engineer, build to the calculations, and coordinate the building control applications and inspections. Planning runs on a separate route through Dacorum Borough Council, and we tell you at survey which consents your scheme needs.
For Hemel Hempstead, 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 Hemel Hempstead: 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 Hemel Hempstead
Hemel Hempstead range: choose above
The plan Dacorum decides your extension against
Dacorum Borough Council is the local planning authority for Hemel Hempstead. Its Core Strategy was formally adopted on 25 September 2013. The Site Allocations Development Plan Document was adopted in July 2017. Saved policies of the Dacorum Borough Local Plan 1991 to 2011, adopted in 2004, remain part of the adopted development plan, so an application is judged against a set of documents rather than a single one.
The council's emerging plan is called the New Dacorum Local Plan, running to 2041. An emerging plan carries weight in decisions before it is adopted, which is one reason a scheme drawn up two years ago is worth revisiting before it is submitted. We are builders rather than planning consultants, so where a scheme looks finely balanced we will say that a planning professional is the right person to advise on it.
Housing in Hemel Hempstead
Count the homes in Hemel Hempstead and you get about 41,110: 89% built since 1945, 6% between the wars and 5% before 1919, with flats at 31% and houses at 69%. 39% of homes here are terraced; a rear extension on a terrace in Hemel Hempstead digs foundations close to both neighbours, so notices to both are normal.
Validating the application, and paying for advice first
Dacorum states that it does not currently have any additional local validation requirements for planning applications beyond the national list. It will not validate an application submitted without the Community Infrastructure Levy additional information forms, so those go in with everything else. Application fees are set nationally. Dacorum directs applicants to the Planning Portal fee calculator rather than publishing its own scale.
Pre-application advice is charged separately. Dacorum charges £235 including VAT for written pre-application advice on a householder extension or outbuilding. It charges £475 including VAT for pre-application advice on an extension to a house that is not listed, and £560 including VAT where the house is listed. The council quotes 20 to 30 working days for a response, so that belongs at the front of the programme rather than in the last fortnight before you want to start.
What is under the footprint
Chalk, with different material sitting over it depending on the neighbourhood. British Geological Survey mapping shows Adeyfield with Lambeth Group and Seaford Chalk Formation bedrock, and records the Clay-with-flints Formation as the superficial deposit there. Grovehill is mapped on Clay-with-flints over Seaford Chalk. Bennetts End is mapped on Head over Lewes Nodular Chalk. At Boxmoor the valley floor is Alluvium over New Pit Chalk, with Head on the lower slopes and the higher ground around St John's on Lewes Nodular Chalk with no superficial deposit mapped.
Clay-with-flints is the one to plan around. The BGS records it as up to about 10 metres thick, but very variable where let down into dissolution pipes in the Chalk, and records that those pipes and hollows may be 1 to 50 metres in diameter. A foundation that is straightforward at one corner of a rear extension can meet something quite different at the next. Trial holes and an engineer's foundation design answer that. A geology map on its own does not.
Public sewers and lateral drains
They set where an extension can go. Thames Water requires a build over agreement if you build within 3 metres of a public sewer, and also if you build within 1 metre of a public lateral drain. A Class 1 build over application, where the internal diameter of the sewer is 175mm or less, costs £130. We raise drainage at survey, because moving a proposed wall costs far less than moving a sewer.
The agreement is applied for by you as the property owner, and we prepare the drawings and drainage details it needs. It runs alongside the building control application rather than after it. Where the position of a sewer is uncertain, a drainage survey before the foundations are designed is cheaper than redesigning them once the trench is open.
Kitchen extensions in Hemel Hempstead
57% of the houses in Hemel Hempstead 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 Hemel Hempstead; the build figures are in the table above.
Side return extensions in Hemel Hempstead
Side returns belong to Victorian and Edwardian terraces, and only 5% of homes in Hemel Hempstead 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 Hemel Hempstead
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 Hemel Hempstead often needs planning permission from Dacorum Borough Council. On the 39% 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.
- Brickwork and mortar matched to the existing elevation
- Foundations, groundworks and steel frames
- Steel goalpost frames where the rear wall opens up
VOA Council Tax stock of properties, March 2025, for all 12 statistical areas in Hemel Hempstead. Counts rounded by the VOA.
The GS Renovation Difference in Hemel Hempstead
An extension here runs on two separate consent routes, and GS Renovation keeps both in step: the planning application your designer submits to Dacorum Borough Council, and the building control applications and inspections that follow it. We appoint the structural engineer, build to the calculations, and keep the two routes in step so that neither holds up the other. Our founder has over 30 years of hands-on experience. We are fully insured and registered in England, company number 14611254, and you deal with one point of contact from survey to handover.
- Insulation and thermal detailing to current regulations
- Weathertight shell reached before the fit-out begins
- Structural engineer instructed and coordinated on your behalf
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…
Saiid did a complete refurbishment of our small bathroom. This involved ripping out the existing bath/shower, basin, toilet, pipework, and tiles and…
FAQ
Frequently Asked Questions about House Extensions Hemel Hempstead
How much should house extensions in Hemel Hempstead cost?
The cost of house extensions in Hemel Hempstead is typically £2,000 to £2,800 per m² for a rear extension (London-derived), and the HP1 survey decides where in that range your job lands. The biggest mover is what the survey finds: the width of the opening into the house decides the steel. GS Renovation shows the Hertfordshire Building Control fee on its own line, and the written figure follows within days of the visit.
Do the Old Town conservation rules apply to an extension in Piccotts End?
Piccotts End is its own conservation area, designated on 6 October 1969, and one of 25 in the borough. Conservation area control applies there in its own right. Piccotts End does not appear on Dacorum's list of completed conservation area character appraisals, so there is no published appraisal setting out what the council looks for. That makes early contact with the conservation team on 01442 228000 more useful there, not less.
There is a mature tree where the extension foundations would go. Is it protected?
Take it that it is, if the property sits inside a conservation area. The Old Town character statement advises that, regardless of whether a tree is covered by a tree preservation order, a tree is likely to be protected if it lies within the conservation area boundary. Works to it are then dealt with through Dacorum before the foundation design is fixed. The conservation team can be reached on 01442 228000.
What shape does a rear extension behind the High Street need to be?
One that follows what is already behind the building line. The character statement asks that the scale, form and massing of existing rear extensions be respected and, where possible, reflected in future alterations and extensions behind buildings fronting the High Street or Queensway. It describes those rear extensions as tall narrow gables projecting perpendicular to the building line, and treats the plot grain, with buildings running down the plot, as very important.
Does the conservation area rule out a side return?
It does not rule one out, but it removes the permitted development route. In the Hemel Hempstead conservation area, planning permission is required for any extension that would extend beyond a wall forming a side elevation of the original house. A side return there is therefore a planning application, decided by Dacorum Borough Council as the local planning authority. We survey and build to the scheme that gets permission, rather than the other way round.
There is a manhole cover where the extension floor will be. What happens to it?
It has to be relocated. Thames Water does not permit internal manholes, so a chamber inside the proposed footprint cannot simply be built over and covered. That work sits with the build over agreement, which Thames Water requires where you build within 3 metres of a public sewer. We raise drainage at survey, because a diverted run can change where the new wall lands and what the foundation has to avoid.
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