Single Storey Extensions — Crowthorne RG45
Open-Plan L-Shape Extension in Crowthorne — Kitchen & Family Room Combined
Location
Crowthorne, RG45
Project Type
Single Storey Extensions
Duration
15 weeks on site
Scope
L-shape rear and side extension, structural steelwork, flat roof, lantern rooflight
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The Brief
A 1972-built semi-detached in Crowthorne, RG45. The rear of the house had a small kitchen and a separate reception room that backed onto a side passage. The clients wanted an L-shape extension — pushing the kitchen back by 4 metres and filling the side passage width with a 2.5-metre-wide side extension, creating one large open-plan kitchen/family room. A feature rooflight lantern was specified to bring light into the centre of the combined L-shape. This single storey house extension is a good example of what's possible on a typical semi — if your property has a similar side passage going to waste, get in touch about your own extension and we'll tell you honestly what your plot can take.
Our Approach
An L-shape extension combining a rear extension and a side infill. The rear extension (4m on a semi) was within standard permitted development. The side infill (2.5m wide — less than half the original house width of 5.8m) also fell within PD limits. Bracknell Forest Council Building Control notified. The structural challenge was the corner of the L — two separate structural openings from the existing house into each wing of the extension, and the corner junction of the flat roof at the internal angle.
The Build
Groundworks completed in two phases — rear strip and then side strip — to maintain access to the house throughout. Cavity brick and block to both wings. Flat roof structure: the rear wing used 175mm C24 joists spanning 4m; the side wing used 175mm C24 joists spanning 2.5m. The corner junction was formed with a 150x150 UC steel post supporting the corner of both roof plates. 150mm Celotex PIR insulation throughout. GRP fibreglass membrane laid as a continuous sheet over both wings and the corner. The rooflight lantern — 2000x1500mm Korniche aluminium — was positioned centrally over the rear wing to maximise impact. Structural opening from existing kitchen into rear wing: 203x133 UC RSJ. Structural opening from existing reception into side wing: 152x89 UC RSJ. Full first-fix electrics to both wings with a unified lighting circuit.
Materials & Specification
Facing brick: Ibstock Anglian Mixture. Cavity insulation: Knauf Dritherm 37. Roof insulation: Celotex FR5000 150mm. Corner post: 150x150 UC section. GRP membrane: laid-up fibreglass roof system. Rooflight lantern: Korniche 2000x1500mm in anthracite.
The Result
The L-shape extension added 27 square metres — 16 square metres in the rear wing and 11 in the side wing. The two wings combine into a single open space of approximately 42 square metres including the existing ground floor rooms opened up to the extension. The Korniche lantern rooflight is the centrepiece of the space, flooding the middle of the plan with natural light. The anthracite frames tie in with the bi-fold door colour specified by the kitchen designer.
Project Photos
L-shape groundworks and foundations — Crowthorne extension
Flat roof structure and Korniche lantern installation — Crowthorne
Completed L-shape open-plan kitchen and family room — Crowthorne RG45
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Project FAQs
Did an L-shape extension need planning permission?
No in this case. Both elements of the L — the rear extension and the side infill — fell within permitted development limits independently. We confirmed this at the initial site visit.
How is the corner of an L-shape flat roof waterproofed?
The GRP fibreglass membrane is laid as a continuous sheet over both wings including the internal corner. The corner junction is formed carefully with a full fillet to prevent water pooling. This is one of the most critical details on an L-shape flat roof and we take particular care with the corner drainage.
How long did the project take?
15 weeks on site. The pre-build phase (building regs, structural engineer, material lead times) added 8 weeks.
Why Choose Berkshire Bespoke Builders
- ✓Owner-managed — Pindi Sahota is on site and managing your job personally
- ✓32 years on the tools — time-served builder, 25 years fitting bespoke kitchens
- ✓Fully insured — public liability and employer's liability on every project
- ✓Fixed-price written quotes — itemised by material and labour
- ✓Building regs managed — we submit applications and attend all inspection stages
- ✓Based in Bracknell — covering all of Berkshire. No travel surcharges or delays
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