- Guide price
- £4,550–£8,350
- Survey
- Free for new and replacement roofs
- Quote
- Fixed, in writing
- Coverage
- England, Wales, Scotland, NI
Dorset at a glance
How much does a green roof cost in Dorset?
Guide prices including VAT at South West rates. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Extension (20 m²), EPDM with sedum green roof | £4,550–£8,350 |
| Extension (20 m²), EPDM, new deck + insulation | £2,900–£5,050 |
Which flat roofs are common in Dorset?
Flat roofs in Dorset sit on 1930s semis with flat-roofed garages and kitchen extensions, shops with flat-roofed rear stores below flats and terraced streets with flat-roofed rear kitchens and bathrooms. The South West averages roughly 1,260 mm of rain a year and many roofs face wind off the Atlantic, so we specify fixings and edge details for wind uplift as well as drainage. Approximate 1991–2020 regional averages based on Met Office data.
Building regulations in England
Replacing more than half of a roof over a heated room usually counts as renovating a thermal element, so it is insulated to current standards and notified to building control. Renovated roofs over heated rooms are insulated to around 0.16 W/m²K where that's feasible, and new extension roofs are built to 0.15 W/m²K. In Dorset the application goes to BCP Council and Dorset Council. More on the rules.
Can my flat roof take the weight of a green roof?
Not every roof can, which is why we check the structure before quoting. A sedum roof is light compared with an intensive garden, but its growing medium holds water, and a saturated build-up adds significant weight to the roof.
We look at the joist sizes, spans and spacing, the condition of the deck and what the roof sits on. On a recently built extension with generously sized joists, an extensive green roof may be straightforward. On an older garage or a roof with undersized or rotten timbers, the structure may need strengthening, or a structural engineer's calculation may be needed before we can go ahead.
In England, a new roof covering that adds 15% or more to the weight of the roof triggers building control approval, and a green roof will often fall into that category. We handle building control where it is needed. The building regulations page covers the approval routes in each nation.
How long does a green roof last and how much maintenance does it need?
A well-built extensive green roof needs one or two maintenance visits a year, and the plant layer can help protect the membrane from sunlight and temperature swings.
Typical maintenance means pulling out weeds and tree seedlings before they root, clearing outlets and the gravel strips around edges, filling in any bare patches, and adding a slow-release feed if the sedum looks thin. Sedum is drought-tolerant once established, but newly laid blankets may need watering in a long dry spell during the first season.
The waterproofing underneath has the same expected life as on any other roof of that system. A green roof also slows down rainwater run-off from the roof and, when sedum flowers, attracts bees and other insects. Some councils encourage green roofs for those reasons, so it is worth mentioning one in a planning application for a new extension. Our maintenance guide covers routine checks.
Which towns in Dorset do we cover?
Green and sedum roofs in Dorset: questions
Which towns in Dorset do you cover?
All of Dorset. The main towns have their own pages below, and if yours isn't listed we still cover it: send your postcode and we'll confirm.
How much does a green roof cost in Dorset?
£4,550–£8,350 for a 20 m² insulated extension roof finished as a sedum green roof, at South West guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Which postcode areas do you cover in Dorset?
All of Dorset, including the BH, DT postcode areas. Send your full postcode and we'll confirm.
Can a green roof have a rooflight in it?
Yes. The rooflight sits on a raised upstand with a gravel strip around it, so the planting stays clear of the glazing and the upstand stays visible and dry.
Can I walk on a green roof?
Only for maintenance, and only where it is safe. Most extensive green roofs on homes aren't designed as roof terraces, and a terrace generally needs planning permission and edge protection.
Can you put a sedum roof on a garage?
Often, yes, if the structure is strong enough. Many older garage roofs have light timbers, so a structural check comes first and strengthening may be needed.
Everything about green and sedum roofs → · All flat roofing in Dorset →