Introduction
One of the most common questions from homeowners planning a loft conversion is: how long will it take? The honest answer is that the on-site build phase is only part of the total duration. Understanding the full timeline from decision to completion helps you plan your household, manage your expectations, and make better decisions about when to start.
Pre-Construction Phase
Before any builder arrives on site, a loft conversion project typically requires:
Architect or designer appointment (1–4 weeks). If you don't already have drawings, appointing a designer and developing concept drawings takes time. For a standard rear dormer, concept drawings can be produced in a few weeks once you've appointed someone.
Planning application (8–10 weeks). If your loft conversion requires planning permission — typically when a rear dormer extends beyond the ridge line or you're in a conservation area — a planning application to a London borough takes 8 weeks as a standard determination period. More complex applications, or those requiring an appeal, take longer.
Structural engineering and technical drawings (3–6 weeks). Once planning is secured (or if PD applies), structural engineer calculations and construction drawings need to be produced before any reputable contractor can give you a reliable fixed price. Rushing this stage typically creates problems later.
Contractor selection and pricing (2–4 weeks). A properly itemised quote from a good contractor takes time to prepare accurately. Allow time to get and compare quotes without feeling pressured into a hasty decision.
Total pre-construction phase: 3–6 months is typical for a standard loft conversion. Projects in conservation areas or with unusual planning complications can take longer.
On-Site Build Phase
For a standard rear dormer loft conversion on a Victorian or Edwardian terrace, the on-site programme is typically:
Scaffolding erection and structural floor: Week 1–2 | Dormer construction and roofing: Week 3–5 | Structural steelwork and staircase: Week 4–6 | Windows, insulation, first-fix: Week 6–8 | Plastering and drying: Week 8–10 | Second-fix joinery, bathroom, electrics: Week 10–13 | Decoration and finishing: Week 13–15 | Snagging and Building Regulations sign-off: Week 15–16
Total on-site duration: 12–16 weeks for a standard rear dormer. Hip-to-gable conversions, larger L-shaped dormers, or schemes combined with other works will add to this programme.
What Extends the Timeline
Client-supplied material delays. Bathroom tiles, sanitary ware, flooring, and other client-supplied items that aren't ordered in advance create programme delays. Order everything early.
Structural discoveries. Unexpected conditions discovered during the build — rotting roof timbers, undersized ceiling joists, hidden drainage — take time to address.
Building Regulations inspections. Certain stages require a Building Control inspector visit before the next stage can proceed. Inspector availability varies by borough.
Weather. External roofing works are weather-dependent. A prolonged wet period during the dormer construction phase can extend the programme.
Realistic Total Duration
For a homeowner starting from scratch — no drawings, no planning, no contractor — pre-construction phase: 3–6 months, on-site build: 3–4 months. Realistic total: 6–10 months from decision to completion. This is not unusually slow. It's the reality of a properly managed, properly approved loft conversion in London.
Planning a loft conversion and want a structured timeline? RCB Design & Build provides detailed pre-construction programmes as part of our design-and-build service. Contact us to discuss your project.
07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk