The short answer
A loft conversion in the UK typically costs between £20,000 and £75,000+, depending on the type, size and complexity. A simple Velux rooflight conversion starts from around £20,000; a full mansard can reach £75,000 or more. The type you choose is the single biggest cost driver — see types of loft conversion to understand which suits your roof.
Loft conversion costs vary so widely that a single headline figure is almost useless without context. A Velux conversion in a modest 1930s semi and a mansard conversion in a London Victorian terrace are structurally different projects with very different contractor requirements, material costs and planning needs. This guide breaks down what you can realistically expect to pay by type, explains the main cost variables and sets out what to expect from quotes so you can compare them meaningfully.
Loft conversion costs at a glance
- Velux / rooflight £20,000–£35,000
- Rear dormer £30,000–£55,000
- Hip-to-gable £35,000–£60,000
- Mansard £45,000–£75,000+
- London / South-East premium 20–40% above national averages
- VAT position Standard rate (20%) usually applies to new conversions
Cost ranges by conversion type
The figures below represent typical total project costs, including structural work, building regulations, insulation, electrics, plastering and basic finishing but excluding furniture and decoration. They reflect national UK averages; London and South-East prices are typically 20–40% higher. These are illustrations of typical costs, not quotes — your property may fall above or below these ranges.
| Type | Typical cost range | Notes |
|---|---|---|
| Velux (rooflight) | £20,000–£35,000 | Simplest; no roof shape change |
| Rear dormer | £30,000–£55,000 | Most common; adds headroom & floor area |
| L-shaped dormer | £40,000–£65,000 | Victorian terraces; wrap-around box |
| Hip-to-gable | £35,000–£60,000 | Semi-detached; rebuilds hipped end |
| Hip-to-gable + dormer | £45,000–£70,000 | Maximises space in hipped semi |
| Mansard | £45,000–£75,000+ | Near-vertical walls; maximum volume |
What drives the cost up or down?
Within each type, a wide range of factors push the final figure higher or lower:
- Roof structure: a traditional cut-rafter roof is cheaper to adapt than a trussed roof, which requires structural redesign. A trussed-roof job typically adds £3,000–£8,000 for the steel frame and engineer’s fees.
- Head height: if the existing ridge height is low, a dormer must create headroom that a better-pitched roof would already have. That structural work is reflected in cost.
- Room layout: a simple bedroom is cheaper than a bedroom-and-en-suite, which requires a plumber, soil stack extension and possibly a waste-water route through the existing structure.
- Materials and finish: UPVC dormer cladding costs less than natural slate or lead; budget finishes cost less than premium; floor coverings vary widely.
- Location: London and South-East labour and material costs are significantly higher than the Midlands or North.
- Party wall: if you share a wall with a neighbour, a party wall agreement is required, adding legal and surveyor fees of £700–£2,000 or more depending on whether both parties appoint surveyors. See party wall agreements.
- Planning fees: if a planning application is required, fees are £258 in England (as of 2026). Architect’s drawings for a planning application typically add £1,500–£4,000.
What the quote should include
A comprehensive loft conversion quote should cover: structural engineer’s design, building regulations application and inspection fees, all main structural work (joists, steels, roof alterations), insulation, fire-resistant plasterboard, staircase supply and fit, electrics (lighting, sockets, smoke alarms), and basic plastering and finishing. Plumbing for an en suite is sometimes priced separately. Get at least three written quotes itemised to the same scope; lump-sum figures are difficult to compare and leave room for dispute.
VAT and financing
Most new loft conversion work is subject to the standard 20% VAT rate; some specific conversions of dwellings may attract a reduced rate, but this is complex and depends on the specific circumstances — your contractor should advise. Some homeowners fund the work via a further advance on their mortgage, which spreads the cost over the mortgage term. Check whether adding the value of the conversion to your property value affects your loan-to-value ratio favourably before making a financing decision. This is general information, not financial advice — consult a mortgage adviser or financial adviser for your situation.
Does the cost stack up?
A loft conversion typically adds 15–25% to a UK property’s value, according to RICS guidance and estate agent surveys, though the figure varies considerably by location, property type and the quality of the conversion. In high-value locations, the uplift can significantly outweigh the cost; in lower-value markets the arithmetic is tighter. See does a loft conversion add value? for a detailed look at the return on investment. This page is general information about typical costs in the UK, not a quote or professional building advice — always obtain written quotes from qualified contractors and check their credentials before proceeding.
Get accurate quotes for your loft conversion
Compare quotes from specialists who will assess your specific roof, confirm what type of conversion is possible and provide a fully itemised price for your project.
Frequently asked questions
How much does a basic loft conversion cost?
A simple Velux rooflight conversion — the least invasive type — typically costs £20,000–£35,000 including building regulations, electrics and basic finishing. A rear dormer, the most common type, typically costs £30,000–£55,000.
Why are London loft conversions more expensive?
Labour rates, material delivery costs and contractor overheads are all higher in London and the South-East, typically adding 20–40% to the cost of an equivalent project compared with the Midlands or North of England.
Are loft conversion quotes usually all-in?
Not always. Some builders quote for construction only, excluding structural engineer fees, building regulations, electrics, plumbing and finishes. Always ask for an itemised quote covering all trades and fees before comparing figures.
Do I pay VAT on a loft conversion?
Yes, most new loft conversion work is subject to 20% VAT. Some reduced-rate reliefs exist for specific conversion or renovation types, but these depend on detailed circumstances. Ask your contractor to confirm the VAT position in writing.
Sources & further reading
- RICS — guidance on home improvement costs, added value and property valuations
- LABC (Local Authority Building Control) — building regulations application fees and inspection requirements
- GOV.UK — planning application fees for householder applications (England, 2026)
- Planning Portal — guidance on permitted development and planning requirements for loft conversions
This is general information about loft conversions in the UK, not professional planning, structural, building or legal advice. Costs are typical illustrations, not quotes; timescales and outcomes vary with your property, location and chosen specialist. Always consult a qualified specialist and your local planning authority before starting work.