How long does a loft conversion take? A week-by-week timeline
How long does a loft conversion take? On site, a dormer loft conversion takes 8 to 12 weeks. A hip-to-gable or mansard takes 10 to 14. Those are the honest ranges from our Bristol projects, and we'd rather give you a range we keep than a date we don't.
We know why you're asking, though. It's rarely curiosity. It's the friend whose "11-week loft" ran for five months, with the family living around a hole in the landing ceiling. So this guide does two things: it walks through what happens in each week of a well-run loft, and it names what stretches a programme, so you can see whether the builder in front of you has planned for it.
How long does a loft conversion take? The short answer by type
| Type of loft conversion | Weeks on site | What pushes it to the top of the range |
|---|---|---|
| Velux / room-in-roof | 6 to 8 | A bathroom, awkward stair position |
| Dormer | 8 to 12 | Large full-width dormer, en-suite, complex fire route downstairs |
| Hip-to-gable | 10 to 14 | New gable masonry, party wall works, dormer as well |
| Mansard | 10 to 14 | Most structure of all; planning conditions |
If you're not sure which one your roof wants, our guide to which loft conversion fits your roof will help. The rest of this article follows a dormer, because that's the Bristol default.
Before week one: the lead times nobody counts
The build isn't the whole wait. Planning permission, where it's needed, takes about eight weeks. Most Bristol lofts are permitted development, but we still recommend a lawful development certificate as proof, and that takes about eight weeks too (Planning Portal); our planning guide explains which applies to you. If steels bear into a shared wall, the Party Wall Act needs two months' notice, and neighbours have 14 days to respond, so allow one to two months; the detail is in our party wall guide. Alongside those, the structural engineer produces the calculations, we lodge the building regulations application, book the scaffold and order the roof windows and steel.
Run in parallel, that's typically three to four months from first conversation to first day on site. We give you a start window at quote stage and confirm the date once the paperwork is in. What we never do is promise a date before it is.
Weeks 1 to 2: scaffold and structure
The scaffold goes up, wrapped if we're cutting a dormer, so the roof is protected from the day we open it. Inside the roof space we clear the loft, take out water tanks where the plumbing allows, and set out the new floor.
The steels arrive, are lifted into the roof, and are bedded onto padstones in the party walls. New floor joists go in between them, sitting above the old ceiling so the bedroom ceilings below are untouched. Building control's first inspection happens here, while everything is still visible; the checks are covered in our building regulations guide. By the end of week two you have a solid floor up there and your house downstairs looks exactly as it did.
Weeks 3 to 5: shell, dormer, weathertight
This is the visible fortnight or so. We strip the section of roof where the dormer sits, frame the dormer in timber, roof it, and get felt and battens on. Then cladding or tiles to the dormer cheeks, lead or proprietary flashings where new meets old, roof windows fitted, and the dormer window installed. Somewhere in week four or five comes the milestone we care most about: weathertight. From this point on, weather stops being a risk to your programme.
Weeks 6 to 8: first fix, boarding and stairs
Insulation goes in to the levels Approved Document L asks for, then studwork for the room layout, then first-fix electrics and plumbing. Building control looks at the insulation before we cover it.
Then the one week that touches your house: the stair. We cut the opening in the landing ceiling, fit the new staircase and close the loft into the house. It's noisy, dusty and unavoidable, and we tell you which week it is before we start. Fire doors, plasterboard and interlinked smoke alarms follow. Our approach to keeping the rest of the house liveable is in the dust question.
Weeks 9 to 12: second fix, snagging and sign-off
Plastering, then second-fix electrics and plumbing, the bathroom if there is one, decorating and flooring. The scaffold usually comes down once the outside is finished, often before the inside is. Building control makes its final visit, tests the alarms, measures the stair, checks the doors, and issues the completion certificate. We walk the loft with you, write the snag list, clear it, and hand over. That certificate is the last item on the programme, and it's the one LABC tells homeowners to hold onto for the day they sell.
What stretches a loft timeline, and how we protect yours
Eleven weeks becomes five months for reasons that are mostly predictable.
- Design changes once the roof is open. Moving the bathroom in week six means new drainage runs and often a new engineer's note. We fix the layout on the drawings, before the scaffold goes up.
- Waiting on decisions. Tiles, sanitaryware, the stair finish. We give you a list of every choice and the week each one is needed by, at signing.
- The open-roof window. Bad weather in weeks three to five can lose days. Wrapped scaffold and a crew that gets to weathertight quickly are the defence.
- What the roof hides. Rotten wall plates, undersized purlins, a chimney nobody mentioned. Older Bristol roofs surprise everyone; our quotes carry a contingency line and we tell you the moment we find something.
- Trades not booked in sequence. This is the big one, and it's why "the builder disappeared for three weeks" is such a common story. A firm running several sites with one crew leaves each of them waiting. We run one crew on one loft until it's finished, and every trade is booked to the programme before we start.
- Paperwork not done before day one. Starting without the party wall award, the calcs or the building control application means stopping later. We don't start until they're in.
That's the whole method: fixed programme in writing, decisions listed with dates, materials ordered before we start, one crew per site, weekly updates from Dan or Craig, and a standing invitation to come and see a site we're working on. One FMB verified review put the result better than we can: "They would begin work at 8am without fail, communicate the process to me at all times… The site was kept immaculately clean and organised."
If your worry is more about the wait for a start date than the build itself, our piece on why the good builders in Bristol are booked out covers how far ahead to plan. If it's the money, our 2026 loft conversion guide prices are published in full.
Frequently asked questions
How long does a dormer loft conversion take?
Eight to 12 weeks on site. Weeks one to two are scaffold and structure, three to five the dormer and weathertight roof, six to eight insulation, first fix and the stair, and nine to 12 plastering, second fix, decorating and building control sign-off. A large dormer with an en-suite sits at the top of the range.
How long does a hip-to-gable loft conversion take?
Ten to 14 weeks on site, and the same for a mansard. Both involve more structure than a dormer: a new gable wall built up in masonry, more roof rebuilt, and often a rear dormer as well, so the weathertight milestone arrives a couple of weeks later.
How long before a loft conversion can start?
Typically three to four months from first conversation to first day on site. That covers planning permission or a lawful development certificate (about eight weeks each), party wall notices (two months for cutting into a shared wall), engineer's calculations and the building regulations application, plus the builder's own diary.
Can I live at home during a loft conversion?
Yes, and almost everyone does. Most of the work happens from the outside and above the existing ceilings, so the house below stays largely as it was until the stair opening is cut, usually around weeks six to eight. That's the one noisy, dusty week, and we tell you when it's coming.
Why do loft conversions overrun?
Mostly for predictable reasons: layout changes after the roof is open, late decisions on finishes, weather during the open-roof weeks, hidden defects in old roof timbers, trades booked out of sequence, and paperwork not finished before starting. A written programme with decision dates and one crew per site removes most of them.
Does the time of year matter for a loft conversion?
Less than people think. The exposed period is only weeks three to five, and wrapped scaffold protects it. Winter builds run fine; the practical constraint is booking early enough, because good diaries fill months ahead whatever the season.
Tell us about your project. We'll call you back within one working day, walk your roof, and give you a written programme alongside a detailed, itemised quote. Start here, or come and see one of our loft conversions in Bristol while it's being built.
