What to expect during your build, week by week

A £40,000 to £70,000 extension is one of the biggest things you will ever pay for, and most people have never lived through a build before. The unknown is the scary part. So here is an honest, plain-English walk-through of how a typical single-storey rear extension or loft conversion actually unfolds, from the week before we lift a tool to the day we hand back your keys.

Every job is different, so treat the timings as a realistic guide rather than a promise. A modest extension often runs 10 to 14 weeks; a loft conversion is frequently quicker. Weather, planning conditions, and surprises hidden behind old plaster can all move things.

Before we start: the boring bit that prevents the big problems

Good builds are won before day one. In the week or two before work begins, expect us to confirm a few things in writing:

A start date and a realistic finish window, not a single optimistic day.
A payment schedule tied to stages of work completed, never a large sum up front.
Who your point of contact is and how to reach them.
Building control and any Party Wall matters sorted. Building control is the council’s safety sign-off on structural work, drainage and insulation. The Party Wall Act covers work near a shared wall with a neighbour, common in Bristol’s terraces around Bishopston, Southville and Redland; if it applies, notices should already be served and agreed.

We will also protect your home before any mess starts: dust sheets and floor protection on walkways, a clear route for materials, and an agreed spot for the skip and the loo. Ask where the team will park and where they will make tea. Small things, but they tell you how organised an outfit really is.

Weeks 1–2: groundwork and getting out of the ground

For an extension, this is the dustiest, noisiest phase and the one that looks alarmingly slow. We dig and pour foundations, which often means a building control inspector visiting to approve the trench before concrete goes in. Drains may be diverted. You will see a lot of muck and not much “building” yet.

For a loft, week one is usually scaffolding, opening up the roof, and getting the structural steels in.

Honest expectation: this stage can stall a day or two if the ground throws up a surprise, like an old drain or soft soil. It is normal, and a good builder will explain it rather than quietly absorb the delay.

Weeks 3–5: walls, steel and “weathertight”

Now it speeds up and feels rewarding. Blockwork and brickwork go up, structural steel beams go in, and the new roof structure takes shape. The big milestone here is weathertight (also called “watertight” or “in the dry”): roof on, openings covered, so rain stays out and the inside work can begin.

If your project connects to the existing house, the disruptive “knock-through” usually happens around now. We will warn you the day before, seal the area with dust screens, and keep it to as short a window as we can.

Weeks 6–9: first fix and the rooms appearing

This is where you start to recognise your home. “First fix” means all the hidden services going in before walls are closed up: electrical cables, plumbing pipes, and any heating pipework. If your project affects your boiler or radiators, this is the moment to confirm the details. (If you want it handled under one roof, that is part of our heating services.)

Then comes insulation, plasterboard and plastering. Expect a quieter, more skilled rhythm and far less banging. Plaster needs days to dry, so the site may look finished but unworkable for a short spell.

Weeks 10–13: second fix and the satisfying finish

“Second fix” is the visible craft: sockets and switches on, taps and radiators connected, doors hung, skirting and architrave fitted, kitchen or bathroom installed. Decorating follows. Floors go down last to protect them.

This is also when small choices you have put off, paint colours, handle styles, tile layout, suddenly need answering. Decide these earlier than you think you need to; a held-up decision is one of the most common causes of a delayed finish.

How communication should work throughout

You should never feel like you are chasing your own build. A reasonable standard looks like:

A brief weekly catch-up, in person or by message, on what is done and what is next.
Notice before noisy or disruptive days (knock-throughs, deliveries, power or water off).
Changes priced in writing before they happen, not sprung on you in the final invoice. Any extra is called a variation; you should approve it before we proceed.

A tidy site is part of this too. Tools away, offcuts cleared, your kitchen and bathroom usable each evening. You are living here; it should never feel abandoned.

The end: snagging and final sign-off

“Snagging” is the final walk-round where we list every little imperfection together, a paint touch-up, a sticking door, a missed bit of sealant, and fix them. Take your time and write it all down; a good builder welcomes a thorough list.

Before the last payment, make sure you have:

The building control completion certificate (essential when you sell).
Certificates for electrical and gas work (and your boiler registration if relevant).
Warranties and manuals for anything installed.
An agreed date for the snags to be done.

Only then is the job truly finished.

If you are weighing up a project and want to know exactly how yours would run, we are happy to come round, talk it through with no pressure, and put a fixed price in writing. Get a free quote, take a look at our recent work, or see the areas we cover across Bristol.