Introduction
"How long will it take?" is usually the second question after "how much will it cost?" on any building project. For loft conversions specifically, the answer varies more than most clients expect — and the variables that drive that variation are worth understanding before you commit to a programme.
Typical Loft Conversion Timescales
Realistic on-site timescales for common loft conversion types in London are as follows. A Velux or roof light conversion with no dormer and no structural changes involves 6–9 weeks on site. A rear dormer conversion with one or two bedrooms runs 8–12 weeks. A hip-to-gable conversion takes 10–14 weeks. An L-shaped dormer on a semi-detached property takes 12–16 weeks. A mansard conversion, which involves substantial roof restructuring, runs 14–20 or more weeks depending on design complexity.
These are on-site durations only. They do not include pre-construction design development, structural engineer calculations, a planning application period (typically 8–10 weeks for standard applications), a Building Regulations application (5 or more weeks for the Full Plans route), or material procurement — steel sections currently run 3–6 weeks lead time for many profiles.
What Extends a Loft Conversion Programme
The roof type has the biggest impact: a hip-to-gable or mansard conversion involves far more structural work than a straight rear dormer. Staircase position matters — if creating the stair landing requires moving walls or doors on the floor below, that adds scope and time. The specification plays a role too: an en-suite bathroom, a Juliet balcony, or bespoke joinery all extend the programme. Party wall matters, where the Act applies, add notice and agreement time before work starts. Planning permission, where required, adds 8–10 weeks of pre-construction time that can't be compressed.
What Compresses the Programme
Good pre-construction information is the biggest factor. When structural calculations, Building Regulations approval, and material specifications are confirmed before the build starts, the on-site programme can run without waiting for decisions mid-project. Appropriate procurement matters too: ordering steel sections and roof windows in advance prevents mid-project stalls. Clear client decisions at the right time also make a difference — second-fix materials are client-supplied on RCB projects, so having finishes chosen before second-fix begins keeps the programme moving without stalls.
How to Plan Your Life Around a Loft Conversion
Most loft conversions don't require the homeowner to vacate the property, though the first few weeks of roof work can be disruptive. Plan for 1–3 weeks of roof open (with temporary waterproofing in place overnight), noise during the structural phase, dust during plastering and internal fit-out, and a lockable stair access once the floor is in place. A good contractor will manage the transition from roof work to internal fit-out in a way that keeps disruption to a reasonable level.
Contact RCB Design & Build to discuss the right conversion type for your property, the realistic programme for your project, and what preparation is needed before the build starts.