Open-Plan L-Shape Extension in Crowthorne — Kitchen & Family Room Combined
A detached property in Crowthorne, RG45. The clients wanted to extend in two directions simultaneously — rear and side — to create a large L-shaped open-plan space combining kitchen, dining, and family room. The signature feature: a Korniche aluminium glazed lantern roof centred over the dining zone, bringing natural light deep into the plan. Fifteen weeks on site for one of the larger single-storey projects we've built in the Crowthorne and Sandhurst area.
Project Summary
- Location
- Crowthorne, RG45
- Property type
- Detached
- Service
- Single Storey Extension
- Extension type
- L-shape, rear and side
- Build duration
- 15 weeks on site
- Roof type
- Flat GRP with Korniche glazed lantern
- Glazing
- Bifold doors, rear + side elevation
- Feature
- Korniche aluminium lantern roof
- Building regulations
- Approved
Build Documentation
From Groundworks to Completion
Stage 1
L-Shape Groundworks
The L-shaped foundation trench required careful setting out — ensuring the two runs were square and level. Total trench length approximately 26 linear metres. Clay-based sub-soil at 700mm. Drainage re-routed around the new foundation perimeter.
Stage 2
Korniche Lantern Installation
The Korniche lantern was the most critical installation stage. A structural padstone curb was built into the flat roof deck to receive the lantern frame. The Korniche system uses extruded aluminium rafters that clip into the base frame — highly accurate installation required. Installed by specialist subcontractor.
Stage 3 — Completed
Dual Bifold Installation
Two separate bifold door systems — one each on the rear and side elevations. Both set into structural openings with padstones and structural lintels. The corner of the extension uses a corner post system where the two bifold runs meet — a structural requirement for the L-shape.
The Brief
The clients had a detached property with a manageable back garden and a redundant side passage. Their vision was a large, premium-specification open-plan space — not just a kitchen extension, but a genuine family room big enough for a large dining table, kitchen island, and a comfortable sitting area. The L-shape maximised the available footprint. The Korniche lantern was specified by the client from the outset.
What We Built
L-shaped single storey extension with a rear run of approximately 5m × 4m and a side run of 3m × 3m — total new floor area approximately 29m². Cavity brick and block construction throughout. Two runs of bifold doors: one in the rear elevation, one in the side elevation. Flat GRP roof covering the majority of the extension, with a premium Korniche aluminium glazed lantern (1800mm × 2400mm) positioned centrally over the dining area. Two RSJ steels: one spanning the rear opening, one spanning the side opening. Party wall notice served for the side extension. Full building regulations approval obtained before commencement.
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
Single Storey Extensions Questions Answered
What is a Korniche lantern roof and why is it more expensive?
The Korniche glazed lantern is a premium aluminium lantern system — thermally efficient, with a hidden gutter, structural aluminium rafters, and solar-control double glazing. It typically costs £3,000–£6,000 for a residential lantern depending on size, compared to £800–£1,500 for a basic lantern. The premium is justified by thermal performance and the dramatic visual effect of overhead light.
Does an L-shape extension need two planning applications?
No. An L-shape extension is a single project and requires a single planning or permitted development assessment. The total footprint, height, and projection are assessed together against the PD limits.
Can you stay in the house during an L-shape extension build?
Yes, on most projects. The main disruption period is the structural opening stage — typically 2–3 days where the old rear wall is opened up and the beam installed. We sequence this carefully and provide temporary protection to maintain weather-tightness overnight.
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