One of the most common questions JM receives from South West homeowners is: “How much does a loft conversion cost?” The honest answer is: it depends — but we can give you clear, specific ranges that reflect real JM project costs across Somerset and Wiltshire in 2025.
Quick Summary: 2025 Loft Conversion Costs in Somerset & Wiltshire
- Velux / Rooflight: £20,000–£32,000
- Standard Dormer: £35,000–£50,000
- Hip-to-Gable: £40,000–£55,000
- Hip-to-Gable + Dormer: £50,000–£65,000
- L-Shaped Dormer: £50,000–£65,000
- Mansard: £45,000–£70,000
Cost by Conversion Type
Velux / Rooflight Conversion Cost
The most affordable way to convert your loft. A Velux conversion uses your existing roof structure, installing high-quality Velux or rooflight windows to bring natural light into the space. No structural extension is required, which keeps costs down significantly.
| Item | Typical Cost |
|---|---|
| Basic Velux (1–2 windows, no dormer) | £20,000–£25,000 |
| Full Velux conversion with en suite | £25,000–£32,000 |
| Timescale | 4–6 weeks |
| Planning permission required? | No — always Permitted Development |
Dormer Loft Conversion Cost
The most popular loft conversion type in the South West. A dormer extends vertically from your existing roof slope, creating a box-shaped structure with full-height walls. JM has completed dormer conversions across Frome, Bath, Trowbridge, and beyond.
| Item | Typical Cost |
|---|---|
| Single rear dormer | £35,000–£45,000 |
| Large dormer with en suite | £40,000–£50,000 |
| Timescale | 8–10 weeks |
| Planning permission required? | Usually not (Permitted Development) |
Hip-to-Gable Loft Conversion Cost
Ideal for semi-detached and detached homes with hipped roofs. JM converts the sloping hip end into a vertical gable wall, dramatically increasing the internal loft space. Often combined with a rear dormer for maximum gain — especially popular in Trowbridge, Warminster, and Melksham.
| Item | Typical Cost |
|---|---|
| Hip-to-gable alone | £40,000–£50,000 |
| Hip-to-gable + rear dormer | £50,000–£65,000 |
| Timescale | 10–12 weeks |
Mansard Loft Conversion Cost
The most extensive conversion type — JM rebuilds the rear roof slope at a near-vertical angle, maximising space and ceiling height. Popular with terraced homes in Bath and Frome. Almost always requires full planning permission, which JM manages on your behalf.
Typical cost: £45,000–£70,000
What's Included in a JM Quote?
JM provides fully itemised, fixed-price quotes. Our quotes include:
- All structural work including steel beams and floor joists
- Roofing and weatherproofing
- Velux or dormer windows (supplied and installed)
- Staircase design and installation
- First fix electrical and plumbing
- Insulation to building regulations standard
- Plasterboard, plastering, and decoration to first fix
- Building regulations application fee
- JM 10-year workmanship guarantee
JM quotes do not include second-fix electrical fittings, bathroom fittings and tiling, or floor finishes — though JM can manage these as optional extras if preferred.
Factors That Affect Loft Conversion Cost in Somerset
Several factors influence the final cost of your loft conversion:
- Conversion type — Velux is the most affordable; Mansard the most expensive
- Property size — larger lofts require more materials and labour
- Specification — premium windows, en suites, and bespoke joinery add cost
- Planning complexity — conservation areas and listed buildings require additional work
- Structural requirements — some older properties require more significant structural work
- Access and site conditions — difficult access can add scaffolding costs
How to Budget for a Loft Conversion in Somerset
JM recommends approaching your loft conversion budget in three stages:
- Get a JM fixed-price quote first — don't budget on estimates; book your free survey and get a real number
- Add a 10% contingency — even with fixed-price quotes, some homeowners choose to upgrade spec during the build
- Consider financing early — many South West homeowners use equity release or home improvement loans to fund their loft conversion
JM's Promise: Fixed Price, No Surprises
When JM gives you a quote, that is your price. We don't add variations, unexpected extras, or surprise invoices. The price you're quoted is the price you pay.
Is a Loft Conversion Worth the Cost in Somerset?
Almost always, yes. Studies consistently show that loft conversions add 15–25% to UK property values. In Somerset and Wiltshire — particularly in Bath, Frome, and Bradford on Avon — the return on investment frequently exceeds the national average due to strong local property demand and relatively affordable conversion costs compared to London.
For a typical £350,000 home in Frome, a loft conversion adding 20% value would increase your property by £70,000 — on an investment of £35,000–£50,000. That's an exceptional return by any measure.
Thinking about a loft conversion in Somerset or Wiltshire? Get your free JM quote →