How much does a double storey extension cost in Windsor?

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A double storey extension in Windsor usually costs between £65,000 and £150,000. The final price depends on size, structure, access, drainage, roof design, specification, and how much work is needed to the existing house. Double storey extensions add space upstairs and downstairs, so the structure, roof tie-in, drainage, and neighbour impact need more careful coordination. Planning risk is higher because height, overlooking, loss of light, and roof massing matter more than on most single storey work. The quote should include foundations sized for two floors, steels, floor structure, roof alterations, stairs or landing changes, and upstairs making good. For Windsor work, a credible builder should talk clearly about temporary works, dust control, access, and how Building Control inspections will be staged. Windsor has more period homes, narrow streets, older drainage, and central conservation constraints than many Berkshire towns. Parking, skips, delivery timing, and neighbour boundaries can be bigger cost variables than the basic floor area. Cost should be read as a range until the house has been inspected and the scope is written down. A dependable price needs assumptions on structure, foundations, access, drainage, finish level, Building Control, and what is excluded. Windsor sits under Royal Borough of Windsor & Maidenhead. Projects near central Windsor, Eton, and older terraces often need careful checks on roof form, frontage changes, overlooking, and heritage setting. Planning permission and Building Regulations are separate. Even if planning is simple, Building Control still needs the relevant structure, insulation, drainage, fire safety, ventilation, electrics, roof work, and final completion evidence for the specific double storey extension. Before agreeing the work, ask for a written scope that names inclusions, exclusions, payment stages, variation process, site protection, waste removal, and who manages the job day to day. That is the difference between a headline price and a buildable quote. Berkshire Bespoke Builders covers Windsor and provides free written quotes for double storey extensions. Pindi Sahota has 32 years on the tools and manages projects personally, with fixed-price quotes once the scope is clear.