Prices, and the list of what is not in them.
Fourteen of the eighteen loft conversion websites we looked at before building this one showed no price at all. Here is ours, by type, with a worked breakdown and an exclusions list you can hold against a competitor's quote.
| Type | Guide range | Typical | On site |
|---|---|---|---|
| RooflightLofts that already have the height. The cheapest honest answer. | £22,500–£30,000 | £27,500 | 6–9 weeks |
| Rear dormerThe standard Victorian or 1930s terrace and semi. The workhorse. | £40,000–£60,000 | £50,000 | 8–12 weeks |
| Hip to gableEnd-of-terrace and semis with a hipped, sloping side roof. | £50,000–£70,000 | £60,000 | 10–14 weeks |
| L-shaped dormerVictorian terraces with a rear outrigger — the back addition. | £45,000–£80,000 | £62,000 | 12–16 weeks |
| MansardWhere you need maximum volume, or the conservation officer insists. | £50,000–£80,000 | £65,000 | 14–20+ weeks |
Guide ranges for Surrey, England. Sources: Checkatrade cost guide (updated March 2026) and the HomeOwners Alliance (updated July 2026), which agree closely. Prices vary by region — city centres typically run higher than the surrounding area. Every one of these is confirmed in writing after a survey — none of them is a quotation.
Conversion types explained
Rooflight
No change to the roof shape at all — a new floor, a staircase, insulation, and rooflights set into the existing slope. If your ridge height works without alteration, anyone selling you a dormer is selling you a dormer.
Rear dormer
A flat-roofed box built out from the rear roof slope, converting a triangle of unusable space into a full-height room. This is the type that turns a marginal ridge height into a usable bedroom with an en-suite.
Hip to gable
The sloping side of the roof is built up vertically into a flat gable wall, squaring off the space. Usually paired with a rear dormer, which is where most of the extra floor area actually comes from.
Mansard
The rear roof is rebuilt at roughly 72° with a near-flat top, producing the most floor area of any conversion. Effectively a new storey, and priced accordingly.
Estimate your own price
Pick your conversion type and whether you want an en-suite — this uses the same real trade costs as the worked example below, just applied to your job instead.
30m² rear dormer, Surrey, mid specification, one en-suite
- Roof coverings£8,250Tiles, lead, felt, guttering, and making good the existing roof
- Internal preparation£7,000Strip out, chimney work, moving tanks and services
- Structural steel£6,000Beams, padstones, and the calculations behind them
- Roof structure alterations£5,000Cutting the opening, new rafters, dormer framing
- Scaffolding£4,750Erection, weekly hire for the full programme, and a highway licence
- Joinery£4,500Doors, skirting, architrave, eaves storage — excluding the staircase
- Project management£4,000Programming, building control liaison, site supervision
- Electrics and plumbing£3,250First and second fix, interlinked alarms, en-suite services
- Staircase£2,750Manufacture and fit, plus landing alterations
- Plastering£2,750Boarding, skim, and the fire-rated linings
- Decoration£1,750Mist coat and two finish coats throughout
The build cost is not the project cost.
Figures are indicative for England and dated to their sources — Checkatrade's cost guide (updated March 2026) and the HomeOwners Alliance (updated July 2026), which agree closely. London and the South East typically run 25–35% above these. A quotation is what you get after a survey; this is what you get before one.
What is in, what is out, and how a change gets priced.
Not one of the eighteen sites we audited publishes this. It is the single reason homeowners cannot compare three quotes, and it is the source of nearly every mid-build argument in this trade.
- Full structural design and calculations by a chartered engineer
- Building control application, inspections and the completion certificate
- Party wall notices drafted and served on every adjoining owner
- Scaffolding, skips, highway licences and all site protection
- Interlinked mains-powered smoke alarms to every level
- FD30 fire doors and the protected stairway upgrade
- Insulation to current Part L, and a summer overheating strategy
- Plastered, decorated and ready to furnish
- Daily clean-down and a final professional clean
- Planning application fee, where one is needed£548
- Lawful development certificate£274
- Party wall surveyor fees, if a neighbour dissents£900–£1,500
- Sanitaryware, tiling and brassware for the en-suite£2,500–£8,000
- Floor coverings£1,200–£4,000
- Fitted wardrobes and bespoke joinery£3,000–£9,000
- Relocating the staircase£4,000–£11,000
- Sprinkler system, where ground floor is open-planQuoted at survey
- Bat survey, where the roof shows evidence£400–£750
Get the number for your house.
A survey takes ninety minutes and costs nothing. You get a feasibility answer that day and a written scope schedule within the week.