Portishead at a glance
- Postcode districts
- BS20
- Population
- about 26,355 (GeoNames)
- Council area
- North Somerset Council
- Building approval
- North Somerset Council building control, or a registered building control approver
- Nearest main town
- Bristol, about 8 miles
- Guide price region
- South West (+3% on West Midlands rates)
Why choose a green roof in Portishead?
Garden rooms and outbuildings in Portishead, as elsewhere, often have small flat roofs that are seen from the house and garden. A sedum finish helps them blend in, provided the structure is strong enough and the roof underneath is built properly.
Portishead's flat roofs are mostly on 1930s semis with flat-roofed garages and kitchen extensions, with plenty on 1960s and 1970s link-detached houses with flat-roofed garages and porches too. 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.
How much does a green roof cost in Portishead?
For Portishead we use South West rates: £4,550–£8,350 is the guide for a 20 m² insulated extension roof finished as a sedum green roof, VAT included. 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 |
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.
What's included?
- Root-resistant membrane or separate root barrier
- Warm or inverted build-up to suit the roof
- Pre-grown sedum blankets laid and watered in
- Gravel strips kept clear around edges and outlets
Building regulations in England
Replacing more than half of a flat roof over a heated room usually counts as renovating a thermal element, so the roof is insulated to around 0.16 W/m²K where that's technically and economically feasible, and the work is notified to building control: the council or a registered building control approver, unless a registered competent person self-certifies it. A roof on a new extension is built to 0.15 W/m²K. Patch repairs, and most unheated detached garages, don't trigger the upgrade. Structural changes, or a new covering that adds 15% or more to the roof's weight, also need approval. More on the rules.
Which nearby areas do we also cover?
Green and sedum roofs in Portishead: questions
Do you cover Portishead?
Yes. Portishead is part of our Somerset coverage, including postcode districts BS20. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building regulations for a flat roof in Portishead?
Where the work needs approval it goes to North Somerset Council building control, or a registered building control approver. We tell you at the survey whether your job needs it and deal with the paperwork as part of the quote.
How much does a green roof cost in Portishead?
£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.
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.