The short answer
Usually yes. Most families stay put. The difficult stretches are when the back wall comes out downstairs, when the wall upstairs is opened into the new room, and the days the water or power is off. A prefab frame shortens the time the house is open to the weather but does not remove those stretches.
Moving out for a whole extension is expensive and rarely necessary. Most families live through it. What helps is knowing which parts of the job are hard to live with, so you can plan around them rather than be surprised.
The early weeks are the easy part
Foundations, drains and the ground floor slab happen outside. There is noise, a skip and mud on the drive, but the house works as normal. With a prefab extension, the factory builds the frame during this time, so there is nothing more on your doorstep.
Crane day
If your frame or modules come by crane, the lift is usually done in a day, sometimes two. Keep children and pets indoors and away from the back of the house while loads are in the air, move cars as the lift team asks, and warn the neighbours. The street may be partly closed. After the lift, the shell can be closed against the weather quickly.
When the back wall comes out
This is the hardest stretch. To join the extension to the house, the rear wall on the ground floor is opened and a steel beam goes in. Often the kitchen is in that wall. Expect:
- dust through the ground floor, however good the sheeting;
- no kitchen for a while, sometimes the longest part of the job;
- a temporary wall of boarding and plastic between you and the site.
Set up a stand-in kitchen in another room: microwave, kettle and fridge on a table, with washing up done in the bathroom or a garden tap. A slow cooker and an air fryer go a long way. Agree with your builder when the water and gas will be off, and for how long each time.
When the wall upstairs is opened
A two storey extension also connects through the wall on the first floor, usually from the landing or a bedroom. That brings dust upstairs, where you sleep. Ask for the opening to be cut as late as possible, once the new room is weathertight, plastered and nearly finished, and sealed off until then.
Power, water and heating
There will be days with the power off while circuits are added, and days with the water off when pipes are extended. Ask for these to be planned and announced, not discovered. If the boiler is being moved or replaced, plan for a few cold days, and have electric heaters ready if the work falls in winter.
Safety and security
The site is your builder’s responsibility while they are working on it, but it is your house the rest of the time. Agree how the house will be closed up each night, especially once a wall is open. Tell your home insurer before work starts; most policies have conditions about building work.
Building control will visit at set stages. You do not need to be there, but someone should be able to let them in.
Does prefab make it easier?
In one way, yes: the frame is made in a factory, so the weeks with a half-built shell and an open roof are fewer, and rain is less likely to hold things up. In another way, no: the wall still comes out, the kitchen still goes, and the inside finishing still takes the time it takes. The honest gain from a two storey prefab extension is less time with the house open to the weather, not a build you barely notice.
When moving out makes sense
Consider a short stay elsewhere if someone in the house has a breathing condition that dust would make worse, if you have a newborn, or if the kitchen and the only bathroom are both out of action at once. A week or two away during the worst of the knock-through is often enough.