Planning a house extension in Poole in 2026? You’re not alone. Rising house prices, limited plots, and growing families mean more homeowners are choosing to extend rather than move. But the big question is always the same:
“How much will my extension cost?”
This guide breaks down realistic 2026 costs, local planning considerations, and what to expect in Poole and wider Dorset, so you can plan with confidence.
1. Typical Extension Costs in Poole (2026)
Construction costs have risen across the UK, but Dorset sits above the national average due to labour demand and coastal logistics.
Average 2026 Build Costs (Poole & Bournemouth Area)
| Extension Type | Typical Cost Range (per m²) | Notes |
| Basic single-storey extension | £2,200–£2,800/m² | Simple form, standard finishes |
| Mid‑range single-storey | £2,800–£3,500/m² | Bifolds, rooflights, better glazing |
| High‑end single-storey | £3,500–£4,500/m² | Large spans, premium glazing, coastal spec |
| Two-storey extension | £3,000–£4,000/m² | More structural work, plumbing, stairs |
| Loft conversion (dormer) | £45,000–£75,000 | Depends on roof form & access |
| Loft conversion (hip‑to‑gable) | £65,000–£95,000 | Common in Parkstone & Broadstone |
| Garage conversion | £18,000–£35,000 | Fastest, most cost‑effective option |
Total Project Costs (Typical Poole Homes)
- Small extension (12–18m²): £35,000–£70,000
- Medium extension (20–30m²): £60,000–£120,000
- Large extension (35–50m²): £110,000–£200,000+
2. What Drives Costs Up or Down?
Cost Increasers
- Large structural openings (steel beams, corner glazing)
- High‑performance coastal glazing (salt‑resistant frames)
- Complex roof forms
- Poor ground conditions (common near the harbour)
- Working in tight access areas (e.g., Penn Hill, Ashley Cross)
Cost Reducers
- Simple rectangular footprint
- Standard roof forms
- Using existing drainage
- Avoiding moving kitchens or bathrooms
3. Planning Permission in Poole (BCP Council)
Poole has unique planning constraints — especially near the coast.
Areas with Stricter Rules
- Sandbanks Peninsula
- Lilliput & Evening Hill
- Conservation Areas (Poole Old Town, Penn Hill)
- Harbour‑facing properties
Common Reasons for Refusal
- Overlooking neighbours
- Excessive bulk or height
- Impact on coastal character
- Poor-quality design
Good News
Many extensions fall under Permitted Development, especially:
- Single-storey rear extensions
- Loft conversions
- Garage conversions
A feasibility review can confirm this quickly.
How to Keep Costs Under Control
- Choose a simple footprint
- Avoid unnecessary structural spans
- Finalise design early to avoid variations
- Use an architect to tender to multiple builders
- Consider phased works if budget is tight
Get a Free Extension Feasibility Review
If you’re planning an extension in Poole, Bournemouth, or Dorset, we offer a free 20‑minute telephone consultation to help you understand:
- Whether your project needs planning permission
- What it’s likely to cost
- How long it will take
- Discuss what design options suit your home
- Potential risks or constraints
Book your free call today and get clarity before you commit.