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How Long Does a Loft Conversion Take in London?
One of the most common questions we get from clients planning a loft conversion is: "How long will it take?"
It's a fair question — especially if you're planning around a growing family, a rental void, or a target date for a sale. The honest answer is that it depends on a number of factors, but here are realistic expectations for typical London projects.
The pre-construction phase: 8 to 16 weeks
Before any build starts, there's a design and approval phase that most clients underestimate in terms of time.
Architectural drawings typically take 3–6 weeks to produce, depending on the architect's workload and the complexity of the project.
If planning permission is required (rather than Permitted Development), the statutory determination period is 8 weeks — though many London boroughs take longer.
Structural engineer calculations are usually commissioned once the design is close to finalised and take 2–4 weeks.
Building Regulations submission — either by Full Plans application or Building Notice — adds further time, though Full Plans approval is typically 5–8 weeks and protects you better throughout the build.
If party wall agreements are needed, notice must be served at least two months before works start.
Total pre-construction time for a typical loft conversion in London: 10–16 weeks, assuming no planning complications.
The construction phase: 8 to 14 weeks
For a standard dormer or hip-to-gable loft conversion with one bedroom and one bathroom, expect a construction programme of:
Weeks 1–3: Structural works — steels, floor beams, staircase opening, ridge and roof structure alterations
Weeks 3–5: Dormer or rooflight construction, weathertightness, window installation
Weeks 5–7: First fix — electrical cabling, plumbing pipes, insulation
Weeks 7–9: Plastering and boarding
Weeks 9–11: Second fix — sanitaryware, lighting, skirting, doors
Weeks 11–13: Decoration and floor finishes
Weeks 13–14: Snagging, Building Control sign-off, handover
Simpler rooflight-only conversions (no dormer) can complete in 6–9 weeks. Larger projects with multiple rooms, bathrooms, or complex structural requirements typically run 12–16 weeks.
What makes loft conversions take longer than expected?
Several factors commonly push programmes beyond the initial estimate:
Late structural information. If the structural engineer's calculations arrive after the build starts, it can create hold points while the contractor waits for approved details.
Staircase conflicts. Fitting a new staircase into an existing upper floor while the house is occupied requires careful sequencing and often more time than expected.
Party wall disputes. If a neighbour appoints their own Surveyor and negotiations extend, the programme may not be able to start on the agreed date.
Hidden roof conditions. Older Victorian and Edwardian roofs sometimes have non-standard or damaged structure that creates additional work once exposed.
Client decision delays. Bathroom tile selection, window handle choices, paint colours — these seem minor but can hold up second fix installation if not confirmed on time.
A realistic total timeline
If you're starting from scratch today — with no drawings, no planning, and no contractor instructed:
Pre-construction: 10–16 weeks Construction: 8–14 weeks Total from decision to handover: 18–30 weeks
That's roughly 5–7 months. For a complex or planning-sensitive project, allow up to 9 months.
How RCB manages the programme
We build a project-specific programme at pre-construction stage and share it with clients before the build starts. That means you know what's happening each week, when you'll need to make decisions, and what milestones determine whether the project is on track.
We don't start construction without having structural details confirmed, Building Regulations submission in place, and the first-fix material schedule agreed. That discipline at the start protects the programme at the end.
If you're planning a loft conversion and want to understand the realistic timeline for your specific project, speak to us.
Call us on +44 7359 872594, email contact@rcbgroup.co.uk, or visit rcbgroup.co.uk to book a consultation.
Kind regards, Vasi J. & rcbGroup team contact@rcbGroup.co.uk www.rcbGroup.co.uk +44 7359 872594 | +44 7448 189592 FMB | TrustMark | Checkatrade | TrustATrader Verified. Insured. Trusted.