Roof terrace cost
Roof terrace and flat roof conversion prices for 2025. In the UK, expect to pay between £6,000 and £50,000, with the typical project around £12,000 (average roof terrace conversion (25m²)). Regional variation, specification tier and site access conditions all shift the final quote.
Homeowners researching this typically also price up decking cost. For wider context, browse our bathroom pricing, kitchen pricing and boiler & heating costs.
Cost table
| Item | Typical range (GBP) |
|---|---|
Basic flat roof terrace (25m²) — Structural check, membrane, decking, railing | £6,000–£14,000 |
Mid-range roof terrace (25m²) — Better waterproofing, composite deck, glass balustrade | £12,000–£25,000 |
Premium roof terrace (40m²+) — Landscaping, lighting, seating area, drainage | £25,000–£50,000 |
Labour costs
Labour typically accounts for 55% of the total project cost in the UK.
| Item | Typical range (GBP) |
|---|---|
Structural engineer assessment | £500–£1,500 |
Waterproofing / roofing contractor | £3,000–£10,000 |
Decking installation | £3,000–£8,000 |
Balustrade / railing | £1,500–£6,000 |
Drainage / outlets | £500–£2,000 |
Materials costs
Materials and fittings make up the remainder of the budget, with specification tier driving most of the variation.
| Item | Typical range (GBP) |
|---|---|
Waterproof membrane (per m²) | £40–£90/m² |
Composite decking (per m²) | £50–£100/m² |
Glass balustrade (per m) | £200–£600/m |
Steel railing | £80–£200/m |
Drainage outlets | £0–£0 |
Factors affecting cost in the UK
- ·Region — London and the South East run 15–30% above national averages.
- ·Specification tier — premium materials and finishes can double the base cost.
- ·Access and site conditions — flats, restricted parking and listed buildings add time.
- ·Scope changes mid-project — late design decisions are the biggest cost overrun driver.
- ·Trade availability — quotes rise 10–20% in peak spring and summer months.
Ways to reduce cost
- ·Use lightweight composite decking on adjustable pedestals over an existing flat roof membrane.
- ·Choose glass balustrades only where view matters — steel or aluminium is 50% cheaper.
- ·Site furniture and planters near the roof edge over load-bearing walls.
- ·Combine terrace install with a planned flat roof replacement.
- ·Get a structural engineer's report before pricing — many roofs won't support occupancy without strengthening.
Frequently asked questions
- Do I need planning permission for a roof terrace?
- Yes — in virtually all cases. Creating a roof terrace involves a change of use of the roof space and will affect neighbours' privacy and overlooking. Planning permission is almost always required, even where the flat roof itself doesn't require permission.
- What is the most important consideration for a roof terrace?
- Structural capacity is the most critical factor. A flat roof designed only to carry a waterproof membrane cannot support people, furniture, or planting without structural reinforcement. Always commission a structural engineer assessment before any other work.
- What is the best flooring for a roof terrace?
- Porcelain pavers on adjustable pedestals are increasingly popular — they allow the waterproof membrane to be accessed for maintenance without lifting the entire floor. Composite decking is also popular and lower cost. All materials must be rated for external use.
Sources & how we estimate
Prices are typical UK ranges compiled by ModernExpert.AI from published trade rates and supplier price lists, and are estimates — always get at least three written quotes. Rules on permissions, safety and certification come from the official sources below. Last reviewed 19 October 2026.
- Planning Portal — Extensions
- GOV.UK — Party Wall etc. Act 1996 explained
- GOV.UK — Building regulations approval
- Planning Portal — Do you need permission?
- ONS — Construction output price indices
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