No two extension projects are the same, and the timelines can differ dramatically depending on the size and complexity of the project. However, we have created an example timeline to give you a rough idea of the key milestones in a typical extension project, the order these are likely to happen in, and an approximation of when they might take place.

Your builder will be able to provide a specific timeline for your project which will help highlight key periods where major decisions have to be made on your part, or when disruption to your daily routine is likely to take place.

Key milestones and timings 
Week 1  Set out. Dig out footings. Pour concrete foundations. First delivery of materials. 
Week 2  Build substructure up to damp-proof course. Install/adjust external drainage routes (where appropriate). Install damp-proof course. Pour concrete oversite/floor structure. Erect scaffolding. 
Week 3  Commence construction of exterior walls 
Week 4  Commence construction of interior walls. Complete construction of exterior walls
Week 5  Install roof structure and begin covering. Complete construction of interior walls 
Week 6  Install windows and doors.  
Week 7  Install/adjust interior drainage (where appropriate). First fix electrics and plumbing. First fix carpentry. 
Week 8  Break through to existing house including installation of steels. Make good all works as a result of breaking through. 
Week 9  Plasterboard and plaster to all areas 
Week 10 Second fix electrics. Second fix plumbing (where appropriate). Install flooring 
Week 11  Complete external works - paving, gardening etc. Install skirting. Commence decorating 
Week 12  Complete decoration. Clean down and remove all waste. Carry out snagging 
Week 13 Final inspection. Handover