A loft conversion is one of the most cost-effective ways to add a bedroom — and significant value — to a UK home. But costs vary enormously depending on the conversion type, your roof structure, location, and specification. This guide gives you real 2026 figures to work from, explains what drives the price, and helps you understand what a contractor’s quote should actually include.
What Does a Loft Conversion Cost in 2026?
The honest answer is that there is no single price. The type of structural work required is the biggest variable. A Velux conversion — which adds rooflights to an existing roof without changing its shape — costs far less than a dormer or mansard, which require significant structural alterations.
| Conversion Type | Typical Cost Range (2026) | Timescale on Site |
|---|---|---|
| Velux / rooflight only | £25,000 – £38,000 | 5–8 weeks |
| Single rear dormer | £45,000 – £65,000 | 8–12 weeks |
| Hip-to-gable (detached/semi) | £48,000 – £68,000 | 8–12 weeks |
| Hip-to-gable + rear dormer | £55,000 – £75,000 | 10–14 weeks |
| L-shaped dormer (Victorian terrace) | £58,000 – £78,000 | 10–14 weeks |
| Mansard (rear or full) | £65,000 – £90,000+ | 12–16 weeks |
All figures are for a typical 3-bed semi in the Midlands or North. Add 10–15% for London and the South East. Scottish costs can run 5–10% lower.
What Drives the Cost of a Loft Conversion?
Structural complexity
A Velux conversion leaves your roof structure almost entirely intact. The main work involves strengthening the floor, installing steel beams, fitting the staircase, and adding rooflights. A dormer requires cutting into the roof, constructing a new framed structure clad in lead and tile or felt, and dealing with more complex waterproofing. A mansard — with near-vertical sides — is essentially rebuilding the entire roof slope.
Staircase position and construction
The staircase is one of the most disruptive elements. If you have a long landing, the structural opening is relatively straightforward. If you need to take space from an existing bedroom or reconfigure the first floor, costs rise. A standard new staircase typically costs £3,500–£6,500 fitted; a bespoke space-saving design can be £5,000–£9,000.
Bathroom / ensuite
Adding an ensuite in a loft conversion typically costs £6,000–£12,000 on top of the base conversion cost, depending on how far away the existing soil stack is and whether the macerator route or gravity drainage is used.
Structural engineer and drawings
Most contractors include this in their quote, but some separate it out. A structural engineer for a loft conversion charges £800–£1,500 for calculations and drawings. Full architectural plans for planning (where required) add another £1,500–£3,000.
Specification and finishes
A conversion priced at £50,000 will typically include insulation, boarding, plastering, and basic joinery — but not kitchen-quality finishes, bespoke storage, or premium glazing. Roof windows vary from around £350 (basic Velux GGL) to £1,500+ (triple-glazed, solar-powered units). A top-specification finish can add 15–25% to the base build cost.
What’s Included in a Typical Loft Conversion Quote?
A reputable contractor’s quote should itemise the following (or clearly state what’s excluded):
- Structural steel work (RSJs, ridge beam if required)
- Floor joists — typically 220mm x 47mm C24 timber at 400mm centres, or engineered joists
- Roof dormer structure (if applicable) — framing, cladding, lead flashing
- Insulation: typically 100mm PIR between joists + 50mm PIR over, achieving U-value ≤ 0.18 W/m²K (Building Regs Part L requirement)
- Roof windows and/or dormer windows
- Staircase and structural opening to floor below
- Fire doors to existing landing (Part B requirement)
- Electrical first and second fix (lighting, sockets, smoke alarms to LD2 standard)
- Plastering and boarding
- Building control application and inspection fees (typically £600–£900 for a local authority application)
Items commonly excluded: carpets, painting and decoration, bathroom suite supply and fit, fitted furniture.
The London Premium
Loft conversions in Greater London consistently cost more. Labour rates for skilled trades — roofers, steelwork erectors, carpenters — run 20–35% above the national average. Material delivery costs are also higher. Expect a single rear dormer to run £55,000–£75,000 in inner London boroughs such as Wandsworth, Lambeth, or Islington.
Party wall agreements are also more common in terraced and semi-detached London housing. A party wall surveyor typically costs £900–£1,800 per side if agreement cannot be reached informally.
Ways to Save Money
Get three itemised quotes. Prices for the same specification routinely vary by 20–30% between contractors. The cheapest quote is not always the best — compare line by line.
Separate out the specialist trades. Some homeowners find savings by directly engaging a structural engineer, separate from the main contractor. This only makes sense if you are experienced at coordinating trades.
Simplify the staircase. A straight staircase is cheaper than a quarter-turn or spiral. Accommodating the staircase within the existing footprint often saves £2,000–£4,000 compared to reconfiguring a bedroom below.
Specify thoughtfully. Roof windows in modest sizes (550 x 980mm) cost half as much as large feature windows. Standard mains-operated openers are far cheaper than solar-powered.
Avoid mid-build changes. Variations during construction are expensive — contractors typically charge 20–40% more for instructions issued after work has started.
Financing a Loft Conversion
Most homeowners finance conversions through a combination of savings and a secured loan or further advance on their mortgage. Typical options:
- Further advance on your mortgage: rates typically base rate + 1–2.5%, subject to your lender’s terms
- Secured loan: rates from around 5.5–9% in 2026 depending on LTV and credit profile
- Personal loan: suitable for smaller conversions (under £30,000); rates 7–14%
A loft conversion that adds a bedroom in most UK markets adds 10–15% to property value — on a £500,000 house that is £50,000–£75,000 in added equity, making the return on a £55,000 dormer look attractive. However, in areas already at the top of their value ceiling, returns can be lower.
Frequently Asked Questions
Does a loft conversion require planning permission? Usually not. Most loft conversions qualify as permitted development provided they stay within volume limits (50m³ for detached/semi, 40m³ for terraced) and certain height restrictions. Mansard conversions and any work visible from the street in a conservation area typically need full planning permission.
Do I need Building Regulations approval? Yes, without exception. All loft conversions require building control approval regardless of planning status. This covers structural calculations, fire safety (escape routes, fire doors, smoke alarms), and insulation standards.
How long does a loft conversion take? On site, 8–14 weeks is the norm for a dormer conversion. Design, planning (if required), and building control preparation typically add 8–16 weeks before work starts. Budget 5–8 months from first conversation to moving in.
Will a loft conversion add value? In most UK markets, yes. Adding a usable bedroom typically adds 10–15% to a home’s market value. An ensuite master bedroom can push this toward 20% in family-focused markets.
Can I live in the house during the conversion? Yes, in most cases. The main disruption occurs during the first week (scaffolding, roof opening) and when the staircase is cut through. Most families manage to stay in situ with modest inconvenience.
