A loft conversion is one of the most cost-effective ways to add space and value to a Bath property. Done properly, it can add a bedroom, an ensuite, a home office — or all three — without losing any garden. But “how much does it cost?” is one of the most misleading questions in construction, because the range is genuinely wide.
Here is an honest breakdown of what you should expect to pay in Bath and the surrounding BANES area in 2026.
Loft Conversion Types and Typical Costs
Velux / Rooflight Conversion — £18,000 to £28,000
The most straightforward option. No change to the roofline — you insulate the existing pitched roof, board the floor, add a staircase, and install Velux windows. Works well for home offices or occasional guest rooms. Head height is the limiting factor: if you have less than 2.2m at the ridge, a Velux conversion may not be viable.
Dormer Conversion — £35,000 to £55,000
The most popular choice in Bath. A dormer extends the roofline vertically, dramatically increasing usable floor space and head height. Most Bath Victorian and Edwardian terraces suit a rear dormer well. Front dormers in conservation areas require planning permission and often face resistance from planners.
Hip-to-Gable Conversion — £40,000 to £65,000
Common on semi-detached and detached properties with hipped roofs. The sloped hip end is replaced with a vertical gable wall, significantly increasing floor area. Usually combined with a rear dormer for maximum space.
Mansard Conversion — £50,000 to £80,000+
Most associated with Bath’s Georgian and Regency townhouses. Changes the roof profile entirely to create near-vertical rear walls with a shallow pitched roof. Substantial structural alteration — almost always requires planning permission, and on listed buildings, listed building consent.
What Drives the Price in Bath Specifically
Property type matters enormously. Georgian and Victorian terraces often have steeper pitches than modern builds — which is good for head height — but party walls, shared chimney stacks and existing roof timbers all add complexity.
Conservation areas add cost and time. A significant portion of central Bath sits within conservation areas or the World Heritage Site buffer zone. Planning applications take longer, materials are restricted, and permitted development rights are more limited. Budget for planning fees and potentially an architect if you’re in a sensitive location.
Specification drives the final number. A dormer with a basic ensuite, standard joinery and painted plasterboard costs considerably less than one with bespoke fitted storage, underfloor heating, a high-specification bathroom and Velux roof lights. The shell is broadly similar; the fit-out is where costs diverge.
Access and scaffolding. Bath’s terraced streets and narrow rear accesses can make logistics challenging. A property with no rear vehicle access typically adds £1,500 to £3,000 for additional scaffolding and materials handling.
What a Fixed-Price Quote Should Include
A proper quote from a reputable Bath builder should itemise:
- Structural alterations (steel beams, trimming, party wall works)
- Roof works (dormer structure, weatherproofing, tiling to match existing)
- Insulation (to current Part L standards)
- New staircase
- First and second fix throughout
- Electrical installation (Part P certification)
- Plumbing and heating (if ensuite)
- Plasterboard, skimming and decoration
- Building regulations application and sign-off
- VAT
If a quote doesn’t break these down, or arrives as a single lump sum, ask for the breakdown before signing anything.
Common Pitfalls
Excluded items. Quotes that look competitive often exclude scaffolding, skip hire, planning fees, structural engineer reports or building control fees. Always ask what is and isn’t included.
Provisional sums. A provisional sum is a placeholder for something the builder hasn’t priced properly yet. Legitimate in some cases, but watch for quotes with large provisional sums on items that should be priceable from the outset.
No mention of building regulations. A loft conversion must be signed off by building control. If a quote doesn’t mention this, ask why.
Getting a Quote in Bath
At Aspect Builds, we provide fully itemised fixed-price quotes for loft conversions across Bath and BANES. No estimates, no provisional sums on priceable items, no surprises on site. We visit your property, assess the structure, and give you a number you can hold us to.