Cost guide · Updated October 2026
Loft conversion cost in London
A loft conversion can give you another room without losing garden space. A rooflight conversion keeps the roof shape; a dormer or mansard changes it. That choice, along with the space available for stairs, has a big effect on cost.
Ready to find builders for your project? Tell us about the work and your current stage. We’ll assess whether we can help with suitable introductions.
Indicative build costs by type and size (incl. VAT)
| Type of loft conversion | Small | Medium | Large |
|---|---|---|---|
| Rooflight (Velux) | £28k – £47kabout 20m² | £42k – £71kabout 30m² | £56k – £94kabout 40m² |
| Rear dormer | £40k – £62kabout 20m² | £59k – £94kabout 30m² | £78k – £125kabout 40m² |
| Hip-to-gable | £43k – £68kabout 20m² | £66k – £103kabout 30m² | £88k – £137kabout 40m² |
| L-shaped dormer | £48k – £74kabout 20m² | £72k – £113kabout 30m² | £97k – £150kabout 40m² |
| Mansard | £53k – £84kabout 20m² | £79k – £126kabout 30m² | £106k – £168kabout 40m² |
Indicative only, not a quote. Based on published UK cost guides checked September 2026, adjusted for London. Includes VAT at 20%. Excludes professional fees, planning, building control, party wall costs, surveys and contingency. The published range spans different finishes, so no separate finish uplift has been added. Ranges use typical UK rates with one broad London adjustment, not prices for a particular street or property.
Floor area is only a rough guide for a loft. Stairs, structural work and fire safety work still need paying for in a small conversion.
Possible additions (incl. VAT)
- En-suite shower roomNxtFind estimate, indicative£9,500 – £18,500
On top of the build cost above, including VAT, London.
What changes the price?
- Changing the roof usually costs more than adding rooflights. Low headroom can also rule out the simpler option.
- The staircase may require work on the floor below, and the existing loft floor may need strengthening.
- Scaffolding, difficult access and an en-suite can take the final price beyond a basic room.
Before you compare quotes
Ask whether the price includes the staircase, structural steel, fire safety work, scaffolding and making good on the floor below. Price an en-suite separately if you want one.
Already have a quote? Explore our limited Quote Check pilot.
Not sure you need planning permission? Check in a few questions.
A worked example
Rear dormer · Medium (about 30m²) in London. Here is how the estimate breaks down.
Example at a glance
- Estimated project cost£59,000 – £94,000 incl. VAT
- Build cost before VAT£49,000 – £78,000
- Not included: fees and permissions incl. VAT£4,500 – £23,500+
- Not included: contingency£5,500 – £14,500
- All-in budget incl. VAT, fees and contingency£69,000 – £132,000+
- Likely time on site7 – 11 weeks
- PlanningOften permitted development, within strict volume limits
Indicative only, not a quote. Based on published UK cost guides checked September 2026, adjusted for London. Includes VAT at 20%. Excludes professional fees, planning, building control, party wall costs, surveys and contingency. The published range spans different finishes; your finish choice has not changed this figure.
Where the money goes (before VAT)
The indicative building work, £49,000 – £78,000 before VAT, split across the stages of the build, so you can see how each quote splits the work.
- Structural work: floor joists and steels£9,000 – £14,000
- Dormer or roof alterations£9,000 – £15,500
- Staircase and forming openings£5,000 – £8,000
- Windows and rooflights£4,000 – £6,000
- First fix: electrics, plumbing and heating£5,000 – £8,000
- Insulation, plasterboard and plastering£7,000 – £11,000
- Fire doors, escape and regulations work£4,000 – £6,000
- Decoration and flooring£6,000 – £9,500
NxtFind estimate, indicative: typical proportions for this kind of project. Yours will differ.
How long it takes
- Time on site7 – 11 weeksOnce work starts. Design, planning and finding the right builder usually take longer than the build itself.
- Planning and permissionsRear dormerMany loft conversions can use permitted development rights, subject to strict limits including a roof volume allowance of 40m³ on a terrace and 50m³ on a semi-detached or detached house. Flats, designated land, Article 4 directions, previous roof alterations and changes to the front roof slope may require planning permission. Building regulations always apply, and the fire escape route and floor strength are the two that catch people out.
Other costs to allow for (before VAT)
None of these are in the estimate above, and they sit outside a builder’s price. Budget for the ones that apply to you.
- Architect or designer£3,000 – £12,000Typically 7–15% of the build cost. Full service, from first drawings to site visits. Drawings-only packages cost far less.
- Structural engineer£500 – £2,000A single beam calculation sits at the bottom of that range. A whole-project package, or a site with awkward ground, costs more.
- Planning application£0 – £548The householder fee in England is £548, set nationally rather than by your council. Draft regulations propose £575 for applications made from 8 December 2026, subject to parliamentary approval. A lawful development certificate or a prior approval costs less, and work that genuinely falls under permitted development needs no application at all. A planning consultant, if you use one, is extra.
- Building control£600 – £1,500+Varies a great deal by council and by project, and again depending on whether you use the local authority or a registered building control approver. Larger jobs run higher still, and VAT may be added.
- Party wall surveyor, where applicable£800 – £3,600Where you share a wall or dig near a boundary. Around £800–£1,800 is typical where both sides agree to a single surveyor handling the matter. It can be materially higher, commonly £1,500–£3,600 per affected neighbour, where each side appoints its own surveyor, and it is charged per neighbour, so a terrace with neighbours on both sides costs more again.
Typical UK ranges, shown before VAT. London and the South East sit at the top of most of them. Professional fees and building control usually carry 20% VAT; planning fees don’t. Together they come to £4,000 – £20,000+ before VAT, or £4,500 – £23,500+ including VAT, the figure in the summary. Planning fees last checked 13 October 2026.
Ready to find suitable builders?
Tell us what you’re planning. We’ll assess project fit before discussing suitable introductions. You’ll also see an indicative budget after submitting. Free for homeowners, with no obligation to appoint anyone.
Find builders for my projectNot ready to talk yet?
Get our free London Extension and Loft Planner: what to sort out and in what order, 15 questions to ask a builder, and a table for comparing quotes.
Sources
- houseup.co.uk, loft conversion costs (2026)
- planningpermissionchecker.co.uk, loft conversion cost in London (2026)
- bestbuilders.co.uk, architect fees (2026)
- mybuilder.com, structural engineer prices
- bookabuilderuk.com, checkatrade.com and hoa.org.uk, party wall surveyor costs (2026)
- planningscout.co.uk, building regulations fees
- planningportal.co.uk fee schedule and legislation.gov.uk, planning application fees
Build costs checked September 2026; planning fees checked 13 October 2026. London adjustment: one London-wide uplift of 30% on UK average build rates, based on the same guides’ “London & the South East add 25–40%”. It is not postcode-level pricing. Figures marked “NxtFind estimate, indicative”, and the split of the build cost by stage, are our own estimates, not taken from a published source.