Types of loft conversion compared
Pick the form that matches your roof first; finish level second. Checkatrade’s 2026 cost guide (typical 30 m² loft) is a useful national ballpark. Figures are averages for budgeting — not quotes — and were listed as last updated March 2026 in the type table (with a detailed dormer breakdown updated October 2026).
| Type (≈30 m²) | Average cost | Typical range | Rough timescale |
|---|---|---|---|
| Velux / rooflight | £27,500 | £22,500–£30,000 | 4–6 weeks |
| Dormer | £50,000 | £40,000–£60,000 | 10–12 weeks |
| Hip-to-gable | £60,000 | £50,000–£70,000 | 10–12 weeks |
| Mansard | £65,000 | £50,000–£80,000 | 8–10 weeks |
| Modular | £45,000 | £30,000–£60,000 | 2–3 weeks on site |
| Shell only | £30,000 | £22,500–£37,500 | 8–10 weeks |
Per m² averages in the same guide sit roughly at £920 (Velux), £1,670 (dormer), £2,000 (hip-to-gable) and £2,170 (mansard). London and complex older roofs sit above these figures. A 50 m² bungalow conversion averages around £75,000 in the same dataset.
Dormer vs mansard loft
Dormer conversions add a boxed projection with vertical walls and a flat or pitched roof. They are the workhorse option on many terraces and semis: more headroom and floor area than rooflights alone, without rebuilding the whole roof. Variants include rear dormer, full-width dormer, L-shaped dormer and side “dog-house” dormers.
Mansard conversions replace sloping roof planes with a steep (often near-vertical) face and a flat or shallow top. You gain the most near-full-height floor plate, which suits two bedrooms plus a bathroom — but structure, scaffolding and roof coverings push cost and visual impact up. Mansards more often need full planning permission, especially on the front elevation.
- Choose dormer when the existing pitch already gives some head height and you mainly need one good bedroom or office at the rear.
- Choose mansard when you need maximum volume and the street (or rear elevation) can accept a rebuilt roof profile.
- Dormer vs mansard loft cost gap on a 30 m² example is typically around £15,000 on Checkatrade’s averages (£50k vs £65k), before London uplifts and high-spec bathrooms.
Hip-to-gable loft conversion
A hip-to-gable loft conversion extends a sloping hip end out to a vertical gable wall. It is common on semi-detached and end-terrace houses where the hip eats the volume you need for stairs and a room. Many projects combine hip-to-gable with a rear dormer.
Expect more structural steel, new gable masonry or frame, and matching roof tiles on the new plane. Checkatrade’s ballpark for 30 m² is about £60,000 (£50,000–£70,000). Party wall agreements are common where the new gable sits on or near a boundary.
Which loft conversion adds most value?
Estate agents care about useable, compliant space: Building Regulations head height on the stair, fire escape route, and a layout buyers recognise as a bedroom. A modest dormer that creates a clean double bedroom and en-suite often recovers more of its cost than an expensive mansard that over-capitalises the house for the street.
- Match the street. If every neighbour has a rear dormer, a front mansard can be harder to sell through planning and harder to value.
- Count real beds. Value usually tracks an extra bedroom that meets mortgage surveyor expectations, not raw m² of eaves storage.
- Mind the staircase. Losing a landing cupboard to a steep stair can erase the “extra room” benefit on smaller houses.
- Budget contingency. Older roofs often need more steel and insulation than the first sketch assumes — keep around 10% contingency.
Worked example: 30 m² rear dormer
Worked example
Semi-detached house, clear head height over part of the loft, aiming for one double bedroom and en-suite. Checkatrade’s dormer average for 30 m² is £50,000. Their published breakdown for that size includes roughly £4,000 project management, £4,750 scaffolding, £7,000 internal preparation, £5,000 roof structure alterations, £6,000 steel, £8,250 roof coverings, plus electrics, joinery, stair, plaster and decoration to reach £50,000.
If quotes come in at £55,000 including a basic en-suite but excluding professional fees, add 10–15% for design and structural engineer input, plus party wall costs if required.
Answer: Budget about £50,000–£60,000 all-in for a typical 30 m² dormer before London premiums — refine with the Loft Conversion Cost Calculator and local quotes.
Planning and buildability
Many loft conversions on houses in England can be permitted development if volume limits, materials and elevation rules are met — but dormers on the principal elevation, mansards, and works in conservation areas often need planning permission. Building Regulations always apply. Confirm head height, fire doors, escape windows and floor loading with your designer; a structural engineer must sign off steels and floor structure.
When you have shortlisted a type, size the budget with the Loft Conversion Cost Calculator. If you are comparing a loft against a ground-floor addition, read the permitted development extension rules and kitchen extension cost guide next.
Velux and modular options
A Velux or rooflight conversion keeps the existing roof shape and adds windows in the slope. It is the fastest and usually the cheapest route when the ridge already gives you enough head height over a good slice of floor. You gain less drama and less floor area than a dormer, but you also avoid much of the steel and roof-covering cost. Checkatrade’s average of about £27,500 for 30 m² is the right starting point for a simple finish — not a luxury bathroom suite.
Modular loft pods advertise short on-site times (Checkatrade lists around 2–3 weeks for modular averages near £45,000). Factory lead times, crane access and planning still apply. Treat modular as a delivery method, not a free pass on Building Regulations or neighbour issues.
Shell-only packages (around £30,000 average in the same 30 m² table) leave you to fit out later. That can spread cashflow, but living with a boarded shell while you save for a bathroom often costs more in temporary heating and second-phase scaffolding than a single continuous contract.
Practical checks before you choose
- Measure head height on site. Marketing sketches assume clear height you may not have between joists and rafters.
- Find the stair drop. The best roof design fails if the stair eats a first-floor bedroom.
- Check services early. Soil stacks, cold-water tanks and solar arrays all constrain dormer positions.
- Ask about temporary roofs. Scaffolding figures in cost guides often exclude a full temporary roof — rain risk is real on long programmes.
- Party wall and neighbours. Hip-to-gable and wrapping dormers commonly trigger Party Wall Act notices.
- Insurance and mortgage. Tell your insurer when work starts; some lenders want Building Control completion before remortgage.
Compare two or three designs on equal floor area and finish level. A £40,000 dormer that creates a genuine double bedroom can beat a £65,000 mansard that leaves awkward eaves storage sold as “flex space”. When the numbers are close, prefer the quieter planning route and the shorter programme — disruption has a cost guides rarely show.
Finish level and hidden costs
Guide averages assume a competent but not luxury finish. Swap in a framed en-suite, underfloor heating and joinery stair and you can add five figures without changing the roof type. Professional fees, Building Control charges, skips and temporary accommodation (if you move out) sit outside many “conversion cost” tables — keep a separate spreadsheet line for each.
Fire safety detailing — FD30 doors, mains-powered alarms, escape windows — is not optional nice-to-have. Neither is proper insulation and ventilation; loft rooms that overheat in summer or drip with condensation fail the comfort test even when they pass a first viewing. Ask your designer how Part B (fire), Part L (conservation of fuel and power) and Part F (ventilation) are being met on your drawings.
If two types cost within 10% on paper, choose the one that keeps the staircase logical and the bathroom stacked above existing drainage. That decision usually ages better than chasing the last square metre of eaves cupboard.
Frequently Asked Questions
What are the main types of loft conversion?
The main UK types are Velux (rooflight), dormer, hip-to-gable, mansard, and modular or shell builds. Choice depends on roof shape, head height, budget and planning constraints.
Is a dormer or mansard loft better?
A dormer usually costs less and suits many pitched roofs when you need extra headroom at the rear. A mansard creates more near-full-height floor area by rebuilding roof planes, so it costs more but can unlock a larger suite of rooms.
When do I need a hip-to-gable loft conversion?
Hip-to-gable is common on semi-detached and end-terrace houses with a hipped end. Extending the hip into a vertical gable creates the volume a dormer alone cannot provide on that side.
How much does each loft conversion type cost?
As of March–October 2026, Checkatrade’s guide for a typical 30 m² loft puts Velux around £27,500, dormer around £50,000, hip-to-gable around £60,000 and mansard around £65,000 (ballpark averages; ranges vary). Always get local quotes.
Which loft conversion adds the most value?
Value depends on local demand for bedrooms and bathrooms, not just build cost. Extra compliant bedrooms and an en-suite usually help most. Over-specifying a mansard on a street of modest semis can be hard to recover in sale price.
Sources
- Checkatrade — Loft conversion cost (2026) — Cost ranges by type for a typical 30 m² loft; last updated March/October 2026 in guide tables.
- Checkatrade — Types of loft conversions — Dormer variants and conversion type overview.
- Planning Portal — Loft conversion — When loft works may be permitted development vs needing planning permission.
When you are ready to estimate materials or cost for your project, open the Loft Conversion Cost Calculator and enter your measurements.