How Long Does a Loft Conversion Take? A Week-by-Week Timeline
Quick Answer
A dormer loft conversion takes 8–12 weeks on site. A Velux conversion can be done in 6–8 weeks. A mansard conversion takes 12–16 weeks. Add 4–8 weeks for pre-construction (structural drawings, Building Regulations, Party Wall notices) and the total programme from instruction to completion is typically 16–24 weeks.
A dormer loft conversion typically takes 8–12 weeks from start to finish. But that figure hides a lot of variation. The type of conversion, the structural condition of your roof, and whether you need planning permission all affect the programme significantly. What follows is a realistic week-by-week breakdown of what happens and when.
Duration by Conversion Type
| Conversion Type | Typical Duration (on site) | Notes |
|---|---|---|
| Velux / Roof Light | 6–8 weeks | No structural changes to roof shape. Fastest option. |
| Dormer (rear) | 8–12 weeks | Most common in London terraces. Requires structural work. |
| Hip-to-Gable | 10–14 weeks | Requires rebuilding one or both hip ends. More complex. |
| Mansard | 12–16 weeks | Significant structural alteration. Usually requires planning. |
| L-Shaped Dormer | 10–14 weeks | Two dormers joined. Common on Victorian terraces. |
Week-by-Week: A Typical Dormer Loft Conversion
What Slows a Loft Conversion Down
Party Wall disputes are the single most common cause of programme delays. If a neighbour dissents, the appointment of a Party Wall surveyor and agreement of an Award adds 4–8 weeks before work can start. Serve notices as early as possible — ideally the day you receive your Building Regulations approval.
Structural surprises are the second most common cause. Older London properties sometimes have undersized or damaged ceiling joists that require additional steel before the loft floor can be formed. A pre-contract structural survey identifies these issues before they become programme problems.
Building Control inspection delays can also add time if the inspector is not booked in advance. Your builder should be booking inspections at least a week ahead of each stage. If they are not, ask why.