Green Roofs Explained: Benefits, Cost & How They Work
A green roof turns a flat roof into a living surface planted with sedum or other vegetation. They look fantastic and do genuine environmental good — but the system beneath the planting has to be perfect, because you can't easily get back to it once it's down.
The types
- Extensive — a thin, low-maintenance layer (often a sedum blanket). Light, hardy and the most common choice.
- Intensive — a deeper substrate supporting shrubs and even small trees; effectively a roof garden. Heavier, needs more structure and maintenance.
The benefits
- Insulation — an extra thermal layer that helps regulate the building.
- Drainage — slows rainwater run-off, helping with SuDS and reducing flood risk.
- Biodiversity — supports insects and wildlife.
- Membrane protection — shields the waterproofing from UV, extending its life.
- Looks — a far nicer outlook than grey membrane, especially when overlooked by other windows.
How they're built
From the deck up: a robust waterproofing membrane, then a root barrier, drainage and filter layers, a growing substrate, and finally the planting. The single most important layer is the waterproofing — get that wrong and the whole build-up has to come off to fix it.
Why leak testing is essential
Because you can't easily access the membrane once the substrate and planting are on, it has to be right first time. On a 1,000 m² green roof in Milton Keynes, we installed a Fatra single-ply system and electronically leak-tested it watertight before any planting went on. That's how a green roof should be done — get the single-ply right, prove it, then plant.
Get expert advice on your roof
JLH are single-ply flat roofing specialists covering Rotherham and across South Yorkshire, backed by a 20-year workmanship warranty. Book a free, no-obligation survey and we'll give you honest advice and a clear, fixed quote.
Frequently asked questions
Do green roofs need much maintenance? +
An extensive sedum roof is low-maintenance — usually a couple of visits a year to weed, feed and check outlets. Intensive roof gardens need more care.
Will my roof take the weight? +
Extensive sedum systems are relatively light, but the structure must be checked. We assess loadings as part of the design before recommending a green roof.
What goes under a green roof? +
A proven waterproofing membrane is the foundation — we use single-ply and leak-test it before the green build-up goes on, so it’s guaranteed watertight first.
Need a flat roof done properly?
Book a free, no-obligation survey across Rotherham & South Yorkshire.