Everybody wants to know how long it takes. Far fewer people ask what it is actually like, which is the thing that decides whether you enjoy it or endure it.
Weeks 1 and 2: Set out and dig
Marking out, breaking ground and digging the trenches. This is the loudest, dirtiest and most alarming looking stage, and it is the one where your garden stops being a garden. The building inspector comes out to look at the open trenches before anything is poured, so there is often a day of apparently nothing happening while we wait for that visit. It is not us being slow.
Weeks 2 and 3: Foundations and slab
Concrete in, blockwork up to damp course level, drainage run and connected, then the floor slab with its insulation and membrane. Progress suddenly looks fast because a shape appears out of the ground.
Weeks 4 and 5: Walls and openings
Brick and block up to plate height with the cavity insulated as we go, and the steels craned or carried in over the openings. Scaffold goes up. From inside the house this is the quietest stage so far, because all the work is happening outside your existing wall.
Weeks 6 and 7: Roof and watertight
Roof structure, covering, flashings, fascias and guttering, then the windows and external doors go in. This is the day it stops feeling like a building site and starts feeling like a room. It is also the psychological turning point for most clients, and if the weather has been against us this is the week that slips.
Week 8: First fix
Electrics and plumbing run through the studs and under the floor, underfloor heating laid if you are having it. Everything gets inspected and signed off before it disappears behind plasterboard, because getting it wrong here is expensive to put right later.
Weeks 9 and 10: Plaster and second fix
Boarded and skimmed, which puts a lot of moisture into the building, so expect it to feel cold and damp for a few days. Then floors down, sockets and switches on, lights in, radiators hung.
Week 11: The breakthrough
The wall between the old house and the new extension comes out. This is the worst week to live through and it is deliberately last. Everything before this point happened outside your existing walls, which is why you have been able to stay in the house. For a few days there is dust everywhere and a hole where your outside wall used to be. Then it is done.
Week 12: Decorating and snagging
Painting, making good, and then we walk the job with you and write down every single thing you are not happy with. That list gets finished. We do not disappear at 95 percent complete, which is the most common complaint about builders in the entire country and the easiest one to avoid.
What makes it take longer
- Weather, particularly during groundworks and roofing
- Something unexpected in the ground, usually drainage or a shallow existing foundation
- Long lead times on glazing, especially large aluminium units
- Waiting on building control inspections at each stage
- Changes of mind mid build, which is the most common cause by a distance
That last one is worth sitting with. Deciding in week seven that the doors should be somewhere else is not a small change, it is a structural one. Get the decisions made before we start and the programme holds.
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