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 have a double-storey extension on your list for a property in Chalfont Saint Peter, we can help from the first measurements to the final clean-up. For a typical home, plan for 14–22 weeks on site, though larger or more complex jobs take longer. We cover postcodes HP8 and SL9 and nearby Gerrards Cross, Rickmansworth and Amersham, and every quote we send is fixed for the scope described in it.
- Guide price
- £67,000–£134,000 inc VAT
- Time on site
- 14–22 weeks on site
- Postcodes
- HP8 and SL9
- Planning rules
- England
- Local area
- Buckinghamshire
- Survey
- Free, with a written quote
What should you budget for a double-storey extension in Chalfont Saint Peter?
In Chalfont Saint Peter, guide figures for a double-storey extension sit at £67,000–£134,000, VAT included. We set them using rates for the South East, currently about 12% above the national guide. The table shows what pushes a project towards either end of the range; your own price is set after a free survey.
| Type of job | What it usually involves | Guide in Chalfont Saint Peter |
|---|---|---|
| Small (15–20m² total) | A compact rear or side extension adding a small room on each floor. | £45,000–£73,000 |
| Typical (30–40m² total) | A larger kitchen or living room below with a double bedroom or en-suite above. | £67,000–£134,000 |
| Large (50m² plus total) | Wide or deep extensions, often with a new bathroom, steelwork and high-spec glazing. | £112,000–£202,000 |
The main things that change the figure:
- Combined floor area across both storeys
- How the new roof joins the existing roof
- Foundation depth, ground conditions and drains to divert
- Scaffolding duration, access and the level of finishes
What does the job include in Chalfont Saint Peter?
- Insulated cavity walls with brick or render to match the house
- First-floor joists, stud walls and new openings upstairs
- Scaffolding for the full build, erected and inspected
- 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 Chalfont Saint Peter?
Buckinghamshire runs from Chiltern villages of brick and flint, through Metroland interwar semis around Amersham and Chesham, to Victorian terraces in High Wycombe and Aylesbury. Milton Keynes adds estates built from the 1970s onwards in brick, render and timber frame, and new housing continues to spread around its edges.
The Chiltern hills are more exposed than the vale below, and clay-with-flints soils make drainage design and footing depth worth checking early.
These patterns matter for a double-storey extension: older walls, roofs and floors in Chalfont Saint Peter can need different materials or extra preparation compared with newer homes.
Planning and building rules in Chalfont Saint Peter
As Chalfont Saint Peter is in England, read the following with that system of planning and building control in mind. We check what applies to your house with the council before you receive a quote.
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.
The four stages
We look at the job
Book a visit and we'll come to you. The survey covers measurements, the state of what's there now and any obvious constraints, so the price that follows is based on your actual home, not an average.
Written quote
We put everything into a written, fixed-price quote: the specification, what's excluded, staged payments and the expected time on site. Take whatever time you need to decide; there's no pressure to commit.
Booking the work
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.
On site to finish
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.
Why homeowners choose us
Double-storey extensions in Chalfont Saint Peter: questions
Will the extension affect my neighbours?
A double-storey extension can affect neighbours' light, outlook and privacy, which is why planning departments look closely at height, depth and window positions. Side windows facing neighbours often need obscure glass. Work near a shared wall may also need party wall notices; the Party Wall etc. Act 1996 applies in England and Wales only. We talk through these points early so the design is realistic.
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.
Can I stay at home during the work?
In most cases, yes. Most people can live at home throughout, and we plan the work to keep disruption down by protecting floors, agreeing working hours and keeping access routes clear. Bigger jobs affecting kitchens, bathrooms or heating may mean a short spell with reduced facilities, and we talk this through with you at the survey.
How much does a double-storey extension cost?
A typical double-storey extension of 30–40m² across both floors costs £67,000–£134,000, 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 will a double-storey extension take?
On a typical home, allow 14–22 weeks on site. Larger projects, older buildings and extra work found once things are opened up can extend that, while simpler jobs may be shorter. Your quote includes an estimate of time on site, and your point of contact keeps you updated on the programme as the work progresses.
Nearby towns
Coverage for Chalfont Saint Peter spans HP8 and SL9. Close by, Gerrards Cross, Rickmansworth and Amersham are covered too, and the rest of our UK-wide area follows the same survey-then-quote process from start to finish.