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Build a P or L-shape conservatory.
Combination styles — P or L wraps around a corner of the house, generous floor area.
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Costs, timelines, pitfalls and the right questions to ask before any conservatories starts on p-Shape & L-Shape Conservatory.
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Top tips
Hiring a conservatories, without the regret.
Four moves that separate a smooth job from a nightmare.
Internal corner leak
The biggest single risk on P/L-shape builds. Insist on a proper box gutter with lead flashing.
Exceeds 30 m² limit
Big builds lose Building Regs exemption — full thermal performance compliance required.
Foundation differential
The two halves of the conservatory may sit on different ground conditions. Single contiguous foundation is the safer detail.
Cost overruns
The "from £18,000" headline rarely accounts for the bigger base, more glass and longer build time. Always price-list itemised quotes.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and a typical week-by-week schedule.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Small P-shape (3.5m × 4.5m)uPVC, mixed pitches
£16k–£26k
Medium P-shape (4m × 5m)uPVC, glass roof
£22k–£36k
Large L-shape (4.5m × 6m)Aluminium frames
£30k–£50k
Brick base + slabBigger base
£3.5k–£10k
Box gutter at internal cornerCritical detail
£500–£1.5k
Underfloor heating (whole)Larger area
£2k–£5.5k
!
Quote spread is typically ± 18% — always get 3 quotes.
Timeline
Mid-size conservatory · week by week
Typical
5 phases · 5 wk
5 phases · 5 wk
W1
W2
W3
W4
W5
Foundations + dwarf wall
Frame + glazing
Roof + ridge
Electrics + flooring
Snags + handover
!
Schedule slips on dependencies — pad each phase by 10–20% for real-world delays.
At a glance
Infographic · VideoThe Conservatories briefing.
Infographic
Conservatories quick-view
Video guide
Conservatories explained
P-shape and L-shape conservatories combine two styles (a Victorian front with a lean-to side, for example) to maximise floor area and wrap around the back-of-house corner. They are the biggest, most expensive conservatory category. Expect to pay £18,000–£45,000 fitted in the UK.
What Does the Work Involve?
The combined-style design means two roof types meeting at an internal corner — the most complex roof junction in the conservatory range. The base is larger, often 25–35 m². The work involves two foundations sets, two brick base profiles, a more complex roof with an internal box gutter at the junction, and twice the glazing area of a single-style equivalent.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Small P-shape (3.5m × 4.5m) | 16,000 | 26,000 | uPVC, mixed pitches |
| Medium P-shape (4m × 5m) | 22,000 | 36,000 | uPVC, glass roof |
| Large L-shape (4.5m × 6m) | 30,000 | 50,000 | Aluminium frames |
| Brick base + slab | 3,500 | 10,000 | Bigger base |
| Box gutter at internal corner | 500 | 1,500 | Critical detail |
| Underfloor heating (whole) | 2,000 | 5,500 | Larger area |
| Lightweight tiled roof | 8,000 | 20,000 | Warm roof, larger area |
How Long Does It Take?
6–10 weeks total. The bigger footprint, more complex base, and more roof detailing add 2–4 weeks over a single-style conservatory.
DIY or Professional?
Professional only. The internal corner box gutter detail is the highest-risk part of the build — any DIY attempt will leak within 1–2 years.
Choosing the Right Tradesperson
Specialist conservatory installer with experience of multi-style builds. Insist on seeing previous P-shape or L-shape installations. Check warranty paperwork, FENSA/Certass and DGCOS membership.
UK Regulations
Same exemption rules — under 30 m² and separated by external doors = Building Regs exempt. Large P-shape builds often exceed 30 m² and become Building Regs notifiable. Permitted development limits apply.
Common Problems
- Internal corner leak: The biggest single risk on P/L-shape builds. Insist on a proper box gutter with lead flashing.
- Exceeds 30 m² limit: Big builds lose Building Regs exemption — full thermal performance compliance required.
- Foundation differential: The two halves of the conservatory may sit on different ground conditions. Single contiguous foundation is the safer detail.
- Cost overruns: The "from £18,000" headline rarely accounts for the bigger base, more glass and longer build time. Always price-list itemised quotes.
Frequently Asked Questions
What's the difference between P-shape and L-shape?
P-shape has one Victorian/Edwardian end and a lean-to extension forming the "leg" of the P. L-shape is two rectangular sections meeting at 90°. P-shape suits properties with one corner; L-shape suits straight-back walls.
When is a P-shape worth the cost?
When you need 25–35 m² of additional floor space and your back garden has the room to take a wrap-around shape.
Will P-shape exceed permitted development?
Often yes — most P-shape builds need planning permission, especially in conservation areas. Check before ordering.
Can I have two different roof styles?
Yes — that's the whole point of P/L-shape. Victorian apex on one side, lean-to on the other. The corner gutter is the critical detail.
How much does the internal corner add to the cost?
£1,500–£3,500 for the corner box gutter, lead flashing and internal valley detail. The bigger glass panels and base also add to overall cost.
Is a P-shape the same value-add as two separate extensions?
Cheaper than two separate extensions due to shared foundations and reduced labour, but adds less value to the property than a brick-built single-storey extension. Most surveyors value glazed extensions at 50–70% of brick-built equivalent.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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