A double-storey extension adds two floors of new space to your house in one build, typically a larger kitchen or living room downstairs with an extra bedroom, bathroom or en-suite above, sharing one set of foundations and one roof.
If you live in Hemel Hempstead and are weighing up a double-storey extension, the starting point is a visit to measure up and talk through what you want, which costs nothing. We cover homes across HP1, HP2 and HP3, and a typical project of this kind in the East of England lands somewhere in the £63,000–£126,000 bracket, including VAT. The exact figure depends on size, access and the finish you choose.
- Guide price
- £63,000–£126,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- HP1, HP2 and HP3
- Planning rules
- England
- Local area
- Hertfordshire
- Survey
- Free, with a written quote
How much does a double-storey extension cost in Hemel Hempstead?
What will a double-storey extension cost in Hemel Hempstead? Our guide range is £63,000–£126,000 including VAT. That figure is adjusted for the East of England, about 5% above the national guide, and is intended for planning a budget. A firm written price for your chosen specification follows a free survey at your home.
| Type of job | What it usually involves | Guide in Hemel Hempstead |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £42,000–£68,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £63,000–£126,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £105,000–£189,000 |
Expect these to shape the final quote:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Bathrooms, en-suites and plumbing on the upper floor
- Scaffolding duration, access and the level of finishes
Scope of the work
- Groundworks, foundations and below-ground drainage
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Electrics, plumbing and heating by qualified trades, with certificates
- Windows, external doors, plastering and internal doors
- Building control inspections and completion certificate
What are homes like around Hemel Hempstead?
Hertfordshire is home to the first garden cities, Letchworth and Welwyn Garden City, and the post-war new towns of Stevenage, Hatfield and Hemel Hempstead. Watford and St Albans have Victorian terraces and Georgian streets, interwar semis line the commuter suburbs, and brick-and-flint cottages appear in Chiltern villages to the west.
Generally dry with chalk and clay soils; clay areas can move in long dry spells, and mature trees near houses need considering for foundations.
In Hemel Hempstead, as elsewhere in Hertfordshire, we take the building's age and construction into account before recommending anything, because both can change what is involved in a double-storey extension.
Permissions for a double-storey extension in Hemel Hempstead
Homes in Hemel Hempstead come under the regulations for England, summarised below. We don't rely on general rules alone: we confirm the position for your address with the council before a quote goes out.
In England, a two-storey rear extension can only be permitted development if it is no more than 3 m deep, at least 7 m from the rear boundary and finished to match the house. Most double-storey and all two-storey side extensions need full planning permission.
Building Regulations approval is needed, with structural calculations for beams, foundations and the roof. The Party Wall etc. Act 1996 often applies on semi-detached and terraced houses.
Rules change and every property is different, so we check the planning history and constraints for your address before we quote.
What happens after you get in touch?
Free site survey
A free survey comes first. It gives us what we need to price a double-storey extension properly, including dimensions, existing materials and access for deliveries, and gives you the chance to ask anything you like.
Written quote
We turn the survey notes into a written quote. The price is fixed for the specification we agree, and the document sets out materials, scope and payment stages in plain language.
Getting ready
Next comes planning the work itself. We set a start date that suits you, line up the right trades, and make sure any approvals for a double-storey extension are in place before the first day on site.
The work itself
During the work we protect the areas around it and tidy up at the end of each day. Once complete, we check the finish, remove our materials and hand over paperwork such as building control sign-off where it applies.
What you can expect from us
Double-storey extensions in Hemel Hempstead: questions
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £63,000–£126,000, built to a plastered finish. As a rough guide, allow around £1,400–£2,600 per square metre plus fixed costs for groundworks, scaffolding and fees. The second storey usually costs less per square metre than the first, because foundations and roof are shared. Bathrooms upstairs and a complex roof add most. We confirm a fixed price after the survey.
How long does a double-storey extension take?
A double-storey extension typically takes 14–22 weeks on site, depending on size, roof design and weather. Foundations and ground-floor walls come first, then the first-floor joists, upper walls and roof. Once it is weathertight, electrics, plumbing, plastering and finishes follow. Allow extra time beforehand for drawings, calculations and approvals. We give you a stage-by-stage programme with your quote.
How is the new roof joined to the existing house?
The new roof is usually tied into the existing roof so the two read as one. On a rear extension this often means a lower ridge or a hipped end, with valleys where the slopes meet. We strip back some existing tiles, fix new rafters and battens, and lay matching tiles or slates. Lead or proprietary flashings seal the junctions so water runs off properly.
What happens at the survey?
We visit your home at a time that suits you, look at the area involved, take measurements and check access, condition and any services that might be affected. We talk through what you want from a double-storey extension, explain the options and answer questions. There is no charge and no obligation; afterwards we send a written quote.
Can you combine a double-storey extension with other work?
Yes. Because we manage several trades under one contract, we can plan a double-storey extension alongside other work on your Hemel Hempstead home, such as new windows with rendering, or a kitchen refit with an extension. Combining jobs can reduce repeat set-up such as scaffolding, skips and access, and every element is listed and priced in the same written quote.
Nearby towns
Whether you're in the centre of Hemel Hempstead or on its outskirts, HP1, HP2 and HP3 addresses are covered. We extend the same service, and the same fixed-price approach, to Berkhamsted, St Albans and North Watford.