- Guide price
- £4,650–£8,500
- Survey
- Free for new and replacement roofs
- Quote
- Fixed, in writing
- Coverage
- England, Wales, Scotland, NI
Hertfordshire at a glance
- Largest towns
- Watford, Hemel Hempstead, Stevenage, St Albans
- Postcode areas
- AL, CM, EN, HP, SG, WD
- Building control
- Watford Borough Council, Dacorum Borough Council, Stevenage Borough Council and 7 other councils
- Neighbouring areas
- Bedfordshire · Buckinghamshire · London · Surrey
- Guide price region
- East of England (+5% on West Midlands rates)
How much does a green roof cost in Hertfordshire?
Guide prices including VAT at East of England 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 | £4,650–£8,500 |
| Extension (20 m²), EPDM, new deck + insulation | £2,950–£5,150 |
Which flat roofs are common in Hertfordshire?
Flat roofs in Hertfordshire sit on newer estates where the first extension roofs are now being replaced, lock-up garage blocks on estates and terraced streets with flat-roofed rear kitchens and bathrooms. The East of England is the driest part of Britain, with parts of the Anglian region around 630 mm a year, so summer heat and UV, not rainfall, do most of the ageing on a felt roof. 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 Hertfordshire the application goes to Watford Borough Council, Dacorum Borough Council, Stevenage Borough Council and 7 other councils. 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 Hertfordshire do we cover?
- Watford
- Hemel Hempstead
- Stevenage
- St Albans
- Welwyn Garden City
- Cheshunt
- Hatfield
- Bishop's Stortford
- Borehamwood
- Hitchin
- Hoddesdon
- Letchworth Garden City
- Harpenden
- Bushey
- Hertford
- Rickmansworth
- Potters Bar
- Berkhamsted
- Ware
- Royston
Green and sedum roofs in Hertfordshire: questions
Which towns in Hertfordshire do you cover?
All of Hertfordshire. 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 Hertfordshire?
£4,650–£8,500 for a 20 m² insulated extension roof finished as a sedum green roof, at East of England guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Which council handles building control for a flat roof in Hertfordshire?
It depends on where the roof is: in Hertfordshire that's Watford Borough Council, Dacorum Borough Council, Stevenage Borough Council and 7 other councils. 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. We confirm which applies at the survey.
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.
Does a green roof leak more than a normal flat roof?
No, as long as it is built correctly. The waterproofing beneath is what keeps water out, and the green layers protect it from sun and weather. The main risk is building it on a weak or ageing membrane.
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 Hertfordshire →