How long will it take? That's the first question. You want to know when the scaffolding goes up, when the stair is cut through the landing, and when the unused loft is a room you can sleep in.
On site, most loft conversions complete in 8–12 weeks. That's the figure on the costs page. Design, permissions and party wall sit before that — typically 4–8 weeks. From first conversation to handover is usually 4–6 months.
The type moves the on-site stretch. How going up works sits in the loft conversion guide. The types themselves sit in loft conversion types.
Key Takeaways
- 1Most loft conversions complete in 8–12 weeks on site
- 2Pre-build — survey, design, permissions, party wall — is typically 4–8 weeks. First conversation to handover is usually 4–6 months
- 3The type sets the on-site stretch: roof-light 4–6 weeks, rear dormer 8–10, hip-to-gable with a dormer 10–12, L-shape 10–12, mansard 12–16
- 4You can usually stay in the house. The work stays in the loft. The stair is the intrusive stretch — two to three days. Noise 8am–6pm. Dust
- 5Party wall notices need two months. Serve them as soon as the design is fixed, not the week before scaffolding
How Long on Site
Weeks on site
Scaffolding up to the final clean
8–12 weeks is the typical construction figure. Scaffolding up to the final clean.
The type moves you through that range — and past it, on a mansard.
| Type | On site | Pre-build |
|---|---|---|
| Roof-light / Velux | 4–6 weeks | 4–6 weeks |
| Rear dormer | 8–10 weeks | 6–8 weeks |
| Hip-to-gable + dormer | 10–12 weeks | 6–8 weeks |
| L-shape | 10–12 weeks | 8–10 weeks |
| Mansard | 12–16 weeks | 10–14 weeks |
A mansard of 12–16 weeks also sits on loft conversion types. Hip-to-gable at 10–12 sits there too.
Typical London bands sit on /costs: dormer £45,000–£75,000, hip-to-gable £55,000–£85,000, mansard £65,000–£110,000. There's no published from-£ for a roof-light conversion. Don't treat those bands as a quotation. Use the calculator for a number on your house.
Before the Scaffolding
This is the stretch people underestimate. Nothing goes on the roof until the survey, the drawings and the permissions are in.
Look at the loft
A site visit. Is a bedroom even possible? A measured survey of the unused space.
Drawings
Architectural drawings. A structural engineer. Revisions until the stair and the room work.
Permissions and notices
Building regulations. Party wall notices if you share a wall. Planning if the scheme needs it.
Get ready to start
Contract. Deposit. Materials ordered. Scaffolding booked.
On a terrace or a semi, the party wall is the one that slips. Most London houses share a wall. Notices have to go out at least two months before work that affects it. Leave it late and the whole job waits.
Planning, if you need it, sits in the planning permission guide. This isn't that guide, and it isn't legal advice.
A Typical Rear Dormer, Week by Week
This is the usual on-site picture for a rear dormer — the conversion most London terraces end up with. A mansard or a hip-to-gable runs longer. A roof-light job is shorter.
Scaffolding and the roof
Scaffolding goes up. The existing roof covering comes off. Temporary weatherproofing goes on so the house stays dry.
The structure
Floor joists strengthened. New steels in. The dormer frame goes up.
The dormer and the roof
Dormer roof finished. Flat-roof membrane on. Windows in. The loft is closed to the weather again.
First fix, and the stair
The staircase goes in. That's the intrusive stretch: two to three days on the landing below. Electrics and plumbing first fix. Insulation.
Boarding and plaster
Plasterboard. Fire boarding. Plaster throughout.
Second fix and the finish
Electrics and plumbing finished. Joinery. Decoration. Flooring. Final clean. The unused loft is a room.
Living in the House
Yes. Most people stay. The work is mostly in the loft. You don't lose a bedroom or the kitchen while it's going on.
Expect noise in working hours, 8am to 6pm. Some dust — keep the doors closed. Occasional power-offs when the electrics are connected. The stair is the week you notice it: two to three days when the landing is a building site.
Moving out can make sense if you have a baby or young children, if you work from home and need silence, or if noise or dust would affect a health condition. The finishing weeks are much quieter.
What Delays the Job
Even a well-planned loft can slip.
Weather. Once the roof is open, you're in the weather. Heavy rain or a strong wind can stop the dormer week.
The existing roof. Old houses surprise you. Rotten timbers, a bodged repair, a different construction than the drawings assumed. Extra work, extra days.
Party wall. If a neighbour doesn't respond, or their surveyor is slow, the process can drag. In extreme cases it adds months.
Decisions left late. Tiles, paint, light fittings — waiting on those holds up the last weeks. Choose them in the pre-build, not once the plaster is on.
What Keeps It Moving
- Decide early. Specs, colours, finishes — before scaffolding, not during it.
- Answer quickly. A question that sits for a week sits on the programme.
- Don't change the job mid-build. A different bathroom or a moved stair adds time and cost.
- Serve party wall notices as soon as the design is fixed. Let that two months run while drawings finish.
The loft conversions page is how Trovix designs and builds these schemes.
If you're considering a loft conversion, book a consultation. We can look at the unused loft, the landing, and a realistic programme for your roof before you commit to drawings.
Which type fits the house sits in loft conversion types. The fuller picture of going up is the loft conversion guide. Planning sits in the planning permission guide. Bands and the calculator sit on /costs.