Double Storey Extension in Windsor — Kitchen Below, Master Bedroom Above
A semi-detached property in Windsor, SL4. The side of the house had a gap — a strip of garden between the flank wall and the boundary — wide enough for a two-storey extension. The client needed both more kitchen space downstairs and an extra bedroom upstairs. A double storey side extension delivered both in a single build. Nineteen weeks — the longest single build on this list, reflecting the structural complexity of two floors of new construction. Full planning permission was required and obtained.
Project Summary
- Location
- Windsor, SL4
- Property type
- Semi-detached
- Service
- Double Storey Extension
- Extension type
- Two-storey side
- Build duration
- 19 weeks on site
- Ground floor
- Kitchen-diner
- First floor
- Master bedroom with en-suite
- Structural steelwork
- Two RSJ beams (ground + first floor)
- Planning
- Full planning permission obtained
- Building regulations
- Approved
Build Documentation
From Groundworks to Completion
Stage 1
Ground Floor Brickwork
Strip foundations at 900mm — the two-storey load required deeper foundations than a single storey. Ground floor cavity walls built to 2.7m ceiling height. Beam pockets formed at both openings at this stage before steelwork installation.
Stage 2
First Floor & Roof
First floor joists laid on wall plates. First floor cavity walls built. Roof structure — cut pitched roof — tied into the existing house roof. The roof junction is the most technically demanding stage of a double storey extension; the ridge must align and the tiles must integrate seamlessly.
Stage 3 — Completed
Mechanical & Electrical
Two full floors of M&E first fix — significantly more than a single storey. En-suite waste stack through the roof, electrical distribution to both floors, heating zone extension to cover new rooms.
The Brief
The client's family had grown. They needed a larger kitchen-diner at ground floor and a master bedroom at first floor — ideally with an en-suite. A double storey side extension was the most efficient way to add approximately 45m² of new floor area across two levels without impacting the garden.
What We Built
Two-storey side extension approximately 4m wide × 5m deep. Cavity brick and block construction on both floors. Ground floor: kitchen-diner with bifold doors to the rear garden. First floor: master bedroom with en-suite shower room. Two RSJ steel beams — one at ground floor spanning the kitchen opening, one at first floor spanning the bedroom opening. Roof tied into the existing house roof structure — matching tile, matching ridge height. Party wall notice served on both neighbours. Full planning permission obtained from Royal Borough of Windsor and Maidenhead.
Why Berkshire Bespoke Builders
- ✓Owner-managed — Pindi on site, personally
- ✓32 years experience — time-served builder
- ✓Fixed-price quotes — itemised, written, no extras
- ✓Building regs managed — submissions + inspections
- ✓Based in Berkshire — Binfield, RG42
FAQ
Double Storey Extensions Questions Answered
Does a double storey extension always need planning permission?
Yes. Double storey extensions are excluded from permitted development. You must submit a full planning application. The Royal Borough of Windsor and Maidenhead has specific design policies — materials must match and roof form must be appropriate. We prepared and submitted the application for this client.
How much does a double storey extension cost?
A double storey side extension in Berkshire typically costs between £90,000 and £130,000 depending on size, specification, and the complexity of the roof junction. It represents better value per m² than two separate projects, which is why clients with the space often choose to do both floors at once.
How disruptive is a two-storey extension build?
More disruptive than a single storey — 19 weeks versus 10–13 for a single storey. The main disruption periods are: structural openings (2–3 days per floor) and the roof junction stage (5–7 days). Clients typically remain in the house throughout, with temporary boarding at any open stage overnight.
More Projects
Related Work
Planning a Similar Project?
Free written quote — usually within 48 hours. Covering all of Berkshire.