Our published guide figures are £25,000–£35,000 for a rooflight conversion, £35,000–£50,000 for a dormer and £45,000–£65,000 for hip-to-gable, with an average around £35,371. What moves a project between brackets is the roof type, the head height, where the stairs can go and whether an en-suite is included.
- A trussed roof costs more than a cut roof, because the structure has to be replaced before the trusses come out.
- Relocating the water tank or changing the heating system is a real cost people forget.
- Fire doors throughout the escape route are part of the job, not an extra.
- Head height decides viability before anything else does.
Our published guide prices
These are the figures we publish across this site. They are planning ranges; every loft is surveyed and measured before it is priced.
| Job | Typical Coventry guide price | Notes |
|---|---|---|
| Velux / rooflight conversion | £25,000–£35,000 | Simplest type |
| Dormer conversion | £35,000–£50,000 | Adds head height & space |
| Hip-to-gable | £45,000–£65,000 | End-of-terrace / semi |
| Average loft conversion | ~£35,371 | Type & extras dependent |
The three types differ in how much structural work is involved. A rooflight conversion changes nothing about the roof shape; a dormer builds out from it; hip-to-gable rebuilds a whole sloping side as a vertical wall.
What pushes a project up a bracket
Roof type: cut or trussed
The biggest single variable. A traditional cut roof — rafters and purlins, typical up to roughly the 1960s — leaves a largely open space and converts readily. A trussed rafter roof has W-shaped webs through the middle, and those cannot simply be cut out: steels and a new structural floor go in first to take the load, then the webs are removed. That is a substantially larger structural job.
Head height
Decides viability before cost. You generally want around 2.2m to 2.4m from the existing floor joist to the ridge underside, because insulation and the new floor both consume height. Marginal head height can sometimes be addressed by lowering the ceilings below or, far more expensively, raising the ridge — but both change the project entirely.
Where the stairs go
Often the hardest part of the design, and it can push the cost up considerably if accommodating a compliant staircase means reconfiguring the floor below. A stair that drops neatly over the existing one is cheap; one that requires moving a bathroom is not.
En-suite
Adds plumbing, drainage and sometimes a pumped waste system where the soil stack cannot be reached with adequate fall. Worth deciding early because it is far cheaper designed in than added later.
The water tank and heating system
A traditional gravity system with a cold water tank in the loft usually has to go, typically replaced with a combi or an unvented cylinder relocated elsewhere. That is a real cost, it affects the whole house, and it is routinely forgotten at budget stage.
What is included that people do not expect
- A new structural floor. The existing ceiling joists cannot carry people and furniture; new joists spanning onto steel beams are required.
- Fire doors to the rooms opening onto the escape stair, usually including existing first-floor rooms, plus upgrading the stair enclosure.
- Mains-wired interlinked smoke alarms throughout the escape route.
- An escape window of specified size in the new room, in most cases.
- A compliant staircase, not a loft ladder — fixed, within pitch and headroom limits.
- Insulation to current standards, usually high-performance board to preserve head height.
- Electrical circuits extended from the consumer unit, which may need capacity checking.
- Building Control application, inspections and the completion certificate.
The fire requirements catch people out most. Converting two storeys into three triggers a substantially higher standard, and the fire doors are not an optional upgrade.
What sits outside the quote
As with any project, the build figure is not the whole budget. Typically outside it:
Design and structural engineering fees. The new floor, the steels, the dormer structure and any gable wall all need calculating.
Building Control fees, paid to the council or an approved inspector.
Party wall surveyor costs, where a dormer or gable involves the party wall — common on terraces and semis.
Heating system changes if the tank has to go and the system is being converted.
Decoration and flooring, depending on the quote.
Contingency — ten to fifteen per cent, and worth holding because what is above an existing ceiling is not fully knowable until it is opened.
Where a conversion is poor value
Worth saying, because loft conversions are generally good value and there are cases where they are not.
Marginal head height. A conversion that produces a room you can only stand up in along the centre line is a poor use of the money, and no amount of clever design fixes the ridge height.
Losing a bedroom to the stairs. If the only place a compliant staircase fits is an existing bedroom, you have converted the loft to replace a room you already had.
Sacrificing the family bathroom. Same logic.
At the street ceiling. If your house is already near the top of what your road achieves, the uplift will not follow the spend.
A heavily trussed roof with low height, where the structural work is substantial and the result is modest.
In any of those cases, an extension or simply moving may be the better answer, and we would say so.
We measure head height, identify the roof type and look at where the stairs could go — the three things that decide it.
Frequently asked questions
How much does a loft conversion cost?
Our published guide figures are £25,000–£35,000 for a rooflight conversion, £35,000–£50,000 for a dormer and £45,000–£65,000 for hip-to-gable, with an average around £35,371. Where a project sits depends mainly on the roof type, head height, the staircase position and whether an en-suite is included.
Why does a trussed roof cost more to convert?
Because the W-shaped webs running through the space cannot simply be cut out — they are carrying the roof. Steel beams and a new structural floor have to go in first to take the load, and only then can the trusses be removed. It is a substantially larger structural job than converting a traditional cut roof.
What costs do people forget on a loft conversion?
Relocating the water tank and often changing the heating system; fire doors throughout the escape route; design and structural engineering fees; Building Control fees; party wall surveyor costs where a dormer involves the shared wall; and decoration. Together those are a meaningful addition to the build figure.
Is a loft conversion cheaper than an extension?
Usually, per square metre, because the roof and foundations already exist and it rarely needs planning permission. It also takes no garden. What it cannot give you is ground-floor living space, so the comparison only works if bedrooms are what you are short of.
Do I need fire doors for a loft conversion?
Generally yes, on the rooms opening onto the escape stair — typically including the existing first-floor rooms — so the stairway stays usable while you get out. Converting two storeys into three triggers significantly higher fire requirements, and the doors are part of the job rather than an upgrade.
How do I know if my loft is tall enough?
Measure from the top of the existing floor joist to the underside of the ridge. You generally want around 2.2m to 2.4m, because insulation and the new structural floor both consume height. Below that the options are lowering the ceilings beneath or raising the ridge, and both change the project substantially.
Three measurements decide it
Head height, roof type and where the stairs can go. We check all three before quoting, and we will tell you if the answer is that it is not worth doing.