Dormer, hip-to-gable, mansard and rooflight conversions. The structure, the staircase, the heating extension and the electrics all come from the same team, which is what keeps a loft on programme.
The roof decides this more than the budget does. Head height, roof pitch and the position of the existing staircase determine what is possible before design begins.
Before anything else, measure from the top of the existing ceiling joists to the underside of the ridge. As a working rule you want around 2.4 metres to have comfortable options — the finished floor build-up and the insulation between and under the rafters will each eat into it.
If you're short, it isn't necessarily over. Lowering the ceilings below or, less commonly, raising the ridge can both work, but they change the job substantially: lowering ceilings means stripping and re-plastering the floor below, and raising a ridge is a planning application in almost every case.
The second constraint is the staircase. Building Regulations set minimum head height over the new stair, and on a narrow terrace finding a compliant run without losing a bedroom below is often the hardest part of the design. It is worth resolving before you fall in love with a layout.
Adding a third storey changes the fire strategy for the whole house, not just the loft. This is the part homeowners are most often surprised by, and it isn't optional.
A loft conversion is unusual among building projects in that most of it happens above your head while you carry on living underneath. The scaffold goes up, the roof is opened and made weathertight, and the structure and first fix happen before the staircase is cut in.
Cutting the staircase is the disruptive moment — that's when the ceiling below opens up and the house genuinely becomes a building site. We sequence it as late as the programme allows and close it back down as quickly as possible.
Typical time on site is 8–14 weeks depending on type, with a dormer at the shorter end and a mansard at the longer. Add design, structural calculations and any planning determination in front of that.
Many rear dormer conversions on a house fall under permitted development, within volume limits and provided nothing extends beyond the existing roof plane at the front. Flats have no permitted development rights at all, conservation areas restrict them, and an Article 4 Direction can remove them. Mansards and ridge alterations almost always need a full application.
Roughly 2.4 metres from the top of the existing ceiling joists to the ridge gives you comfortable options once the floor build-up and rafter insulation are allowed for. Below that it can still be done by lowering the ceilings beneath, but that's a materially larger and messier job and we'd rather set that expectation at the survey.
Usually, yes. Once you have a third storey, Building Regulations require a protected escape route from the loft down to the final exit — in practice that means fire doors to habitable rooms off the stairwell on every floor, plus interlinked mains smoke alarms. It's a real cost and we include it in the quote rather than discovering it at inspection.
Most people do. The bulk of the work happens above the existing ceiling and off a scaffold. The exception is the week or so around cutting in the staircase, when the floor below is genuinely disrupted.
If the new floor joists or a steel bear into a shared wall — which on a terrace or semi they almost always do — then yes, notice needs serving. Two months before work starts for party structure notices.
What it costs, what consent you need, and what to check before taking a quote.
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