Cost guide
How much does a loft conversion cost in Berkshire?
A loft conversion in Berkshire typically costs £26,000 to £104,000 to build, before VAT and fees, depending on the type. A typical 30m² rear dormer comes to £46,000 to £78,000, or about £60,000 to £106,000 once drawings, a structural engineer, building control, a party wall surveyor and VAT are added. These estimates come from published cost guides adjusted for the South East; they are not quotes.
Last reviewed 22 September 2026. Based on our research into official and published sources, listed at the end of this page.
Costs by type of conversion
| Conversion type | Floor area | Typical build cost | Build time |
|---|---|---|---|
| Velux or rooflight | 30m² | £26,000 to £39,000 | 4 to 6 weeks |
| Rear dormer | 30m² | £46,000 to £78,000 | 10 to 12 weeks |
| L-shaped dormer* | 30m² | £46,000 to £78,000 | 10 to 12 weeks |
| Hip to gable | 30m² | £57,000 to £91,000 | 10 to 14 weeks |
| Hip to gable with rear dormer* | 30m² | £57,000 to £91,000 | 10 to 14 weeks |
| Mansard | 30m² | £57,000 to £104,000 | 12 to 16 weeks |
| Bungalow | 50m² | £72,000 to £114,000 | 10 to 12 weeks |
Ranges, not quotes. Build cost only: excludes VAT, professional fees, planning and building control. Last updated September 2026.
* Estimated from the per-m² rate of a related type: no established source prices it separately.
Sources: Checkatrade, Loft conversion cost: 2026 UK price guide (March 2026 (table), August 2026 (breakdown)); Homebuilding & Renovating, Loft conversion costs (Tim Phillips, quantity surveyor) (29 July 2026).
For the rest of the UK, and for your own loft size and finish, use the loft conversion cost calculator. To compare types in detail, see dormer, hip-to-gable, mansard, Velux and bungalow conversions.
Quick estimate
A shorter version of the calculator. Open the full calculator to add extras, fees and VAT.
Estimated build cost
£57,000 to £91,000
South East (including Berkshire), 30m², before VAT and fees
Hip to gable, 1 bedroom with en-suite, standard finish.
- Typical build time
- 10 to 14 weeks on site
- Planning
- This may be allowed under permitted development or may need planning permission, depending on the size and your property. Planning guide
An estimate to help you budget, based on published cost guides. It is not a quote. Figures are reviewed and updated over time. How we calculate this.
Costs by house type
Checkatrade's UK averages by house type (March 2026) are around £50,000 for a terraced or semi-detached house, £62,500 for a detached house, where conversions are often larger or combine styles, and £75,000 for a bungalow, based on a bigger 50m² roof space. Homebuilding & Renovating says projects in the South East, including Berkshire, can cost 15% to 30% more than comparable projects elsewhere.
Cost against house prices, by town
Build costs are broadly similar across Berkshire, but house prices are not. This shows what a typical 30m² rear dormer (£46,000 to £78,000 to build) represents against the median price of a semi-detached house in each town.
| Town | Median semi-detached price, 2025 | Dormer build cost as a share |
|---|---|---|
| Windsor | £595,000 | 8% to 13% |
| Ascot | £550,000 | 8% to 14% |
| Twyford | £550,000 | 8% to 14% |
| Maidenhead | £529,000 | 9% to 15% |
| Wokingham | £497,000 | 9% to 16% |
| Slough | £478,000 | 10% to 16% |
| Bracknell | £455,000 | 10% to 17% |
| Reading | £443,000 | 10% to 18% |
| Newbury | £380,000 | 12% to 21% |
What the build cost covers
Checkatrade's breakdown of a typical 30m² dormer conversion (August 2026) shows where the money goes: project management, scaffolding, internal preparation, alterations to the roof structure, steelwork, roof coverings, electrics and plumbing, joinery, the staircase, plastering and decoration. Roof work and structure are the biggest share.
The build figures on this site do not include:
- VAT, which is generally charged at 20% on work to existing homes (HMRC VAT Notice 708), unless your builder is not VAT registered;
- professional fees: architectural drawings (£1,000 to £4,000) and a structural engineer (£750 to £2,500);
- planning: a householder application (£548) or lawful development certificate (£274), both in England from April 2026;
- building control: £726 to £1,385 for a loft conversion across Berkshire's councils, depending on the council and the size (the lowest, Slough's, dates from 2019; see our council sections);
- party wall surveyor: £900 to £2,700 per neighbour, where needed (see party wall agreements);
- extras such as an en-suite (£4,000 to £10,000), extra rooflights (£750 to £1,800 each) or built-in storage.
Costs people forget
Checkatrade lists architect drawings, structural engineer calculations, planning fees, party wall agreements, bat surveys (£400 to £750 if required), upgrading insulation, and interior finishing as extras that are easy to overlook, and estimates they can add 10% to 15% to a budget. Older roofs can also need more strengthening than expected once work starts.
A worked example
A 30m² rear dormer on a semi-detached house in Wokingham, standard finish, with a lawful development certificate, drawings, a structural engineer, one party wall neighbour, building control and VAT:
- Build: £46,000 to £78,000
- Lawful development certificate: £274
- Architectural drawings: £1,000 to £4,000
- Structural engineer: £750 to £2,500
- Party wall surveyor: £900 to £2,700
- Building control: £1,055
- VAT at 20%: £9,700 to £17,500
- Total: £60,000 to £106,000
How these figures are worked out
We start from Checkatrade's UK cost ranges by type, raise the low end by 15% and the high end by 30% for the South East following Homebuilding & Renovating, and add fees from GOV.UK and each council's published charges. The full method is on the calculator page. These are research-based estimates, reviewed regularly; your quotes will depend on your roof, your home and the specialist you choose.
Frequently asked questions
How much should I expect to pay for a loft conversion in Berkshire?
For a typical 30m² conversion, expect roughly £26,000 to £39,000 for a Velux conversion, £46,000 to £78,000 for a rear dormer and £57,000 to £104,000 for a mansard, before VAT and fees. With professional fees, building control and VAT, a typical dormer project comes to about £60,000 to £106,000. These are estimates from published cost guides adjusted for the South East, not quotes.
What is the cheapest way to convert a loft?
A Velux or rooflight conversion is usually cheapest, because it adds windows to the existing roof slope without changing the roof structure. It only works if the loft already has enough head height. Keeping the layout simple and choosing a standard finish also keeps costs down.
How much does a loft conversion cost per square metre?
Checkatrade gives UK averages of about £920 per m² for a Velux conversion, £1,670 for a dormer, £2,000 for hip-to-gable and £2,170 for mansard (March 2026). Homebuilding & Renovating gives £1,800 to £4,000+ per m² excluding VAT, depending on the finish (July 2026). Costs in the South East tend to sit above national figures.
Are there hidden costs in a loft conversion?
The usual extras are architectural drawings, structural calculations, planning or lawful development certificate fees, building control, party wall agreements, sometimes a bat survey, and finishing work such as flooring and storage. Checkatrade estimates these can add 10% to 15% to a budget.
Sources
- Checkatrade, Loft conversion cost: 2026 UK price guide (March 2026 (table), August 2026 (breakdown))
- Checkatrade, How long does a loft conversion take? (August 2026)
- Homebuilding & Renovating, Loft conversion costs (Tim Phillips, quantity surveyor) (29 July 2026)
- GOV.UK, Planning fees: annual indexation from 1 April 2026 (1 April 2026)
- Checkatrade, Cost to add an ensuite bathroom (June 2026)
- Checkatrade, Balcony installation cost (Juliet balcony) (September 2026)
- Checkatrade, All you need to know about Velux windows (September 2024)
- Checkatrade, Fitted wardrobes cost (March 2025)
- Checkatrade, Underfloor heating cost (March 2026)
- Checkatrade, Party wall surveyor cost (June 2026)
- HM Land Registry Price Paid Data (standard sales) (2025)
- HMRC, Buildings and construction (VAT Notice 708)
This guide is general information to help you plan. It is not legal or professional advice: check your own project with your council or a qualified professional.
Get free quotes from local specialists
Tell us about your project and we’ll pass it to up to three local loft conversion specialists.