The real question isn’t “how long does it take” — it’s “when do I need to start?”
A lot of clients ask about timeline because of their kids — when they can safely do the noisy, disruptive part of the build without it clashing with study time, exams, or the school holidays themselves. “How long does a loft conversion take” is the search term, but the real question underneath it is: if I want this finished by a certain date, when do I actually need to pick up the phone?
Here’s the full sequence, so you can count backwards from whatever date matters to you.
The full timeline, step by step
- Measured survey — around a week to book, results back within two weeks
- Design and review — three weeks on average, though it can be turned around in as little as 24 hours if needed
- Planning permission (household application or Lawful Development Certificate) — 8 weeks
- Building regulations plans and structural calculations — 3 weeks
- Building control approval — 1 to 8 weeks depending on whether you go through the local authority or a private building control inspector
- Party wall notice — must be served a minimum of 2 months before work starts, if a party wall’s involved
- Construction— 8 to 10 weeks, assuming no material delays
Add it up and you’re looking at roughly 24 to 28 weeks from first sketch to handover in a best-case scenario — and it can stretch to 32 weeks or more if there’s back-and-forth on drawings or the local authority’s building control team is running slow.
Counting backwards from the date that matters to you
That six-to-eight-month runway is the bit most people don’t factor in. A few real examples:
- Want it finished before the summer holidays, so the kids have their new rooms for the school break? You need to have instructed a builder by roughly January.
- Want it finished before exams — GCSEs or A-levels typically running through May — so there’s no construction noise during revision? You realistically need to start the whole process, planning included, around September the year before.
The bottleneck isn’t usually the build itself. Construction is the most predictable part of the whole process at 8 to 10 weeks. The real variable is everything that happens before a single tool touches the roof: planning, building regs, and — if you’re not using a Lawful Development Certificate route — the 8-week planning window specifically. If you’re relying on a local authority for building control approval rather than a private inspector, that stage can also be the slowest link in the chain.
What this means if you’re planning around your kids
If avoiding disruption during term time or exams is the priority, the conversation needs to start well before you think it does. Waiting until the Easter holidays to first call a designer, hoping to be finished by summer, simply isn’t enough runway once planning and building regs are factored in properly.
The earlier you start the paperwork stages, the more control you have over exactly when the noisy, disruptive construction phase actually falls.
Read more: Do You Really Need Building Regs?
