Every project is different, but most house extensions follow a similar sequence of stages. Knowing roughly what to expect makes it easier to plan around the work.
Before work starts on site
- Design and drawings: from a rough sketch to detailed plans, often a few weeks depending on how quickly decisions are made
- Planning permission, if needed: councils have a statutory determination period, commonly around eight weeks for a typical household application, though it can run longer
- Party wall matters: notice periods and, if needed, a surveyor’s award can add several weeks where a neighbour is affected
- Building Regulations and finalising the specification, and getting quotes from builders
On site
Once work starts, a single-storey rear extension on a typical home is often measured in a small number of months on site rather than weeks, and a larger or double-storey extension takes longer again. Groundwork and structural work tend to take longer than they look, because so much happens below ground or behind walls before anything is visible above them.
What can lengthen a project
- Ground conditions or below-ground surprises, such as old foundations or drains
- Changes to the design or specification after work has started
- Lead times on bespoke items such as windows, doors or kitchens
- Weather, for groundwork and roofing stages
- How quickly decisions and payments are made along the way
Living around the work
Most homeowners stay in the house during an extension, though which rooms are usable changes as the work moves through the building. We will talk through what to expect at each stage before work starts, so there are no surprises.
This guide is general information for homes in England and is not legal or planning advice. Rules can change and differ between properties and local authorities, so always confirm the position with your council or a qualified professional.
For a timeline specific to your project, ask for a site visit or see our extensions page.