Johnstone at a glance
- Postcode districts
- PA5
- Population
- about 15,930 (GeoNames)
- Council area
- Renfrewshire Council
- Building approval
- Renfrewshire Council building standards
- Nearest main town
- Paisley, about 3 miles
- Guide price region
- Scotland (−5% on West Midlands rates)
Why choose a green roof in Johnstone?
If you're replacing an old flat roof in Johnstone, it's worth deciding whether to add sedum at the same time. If the structure can take it, that is the ideal moment, because the waterproofing is new and the green layers won't need lifting for a long time.
In and around Johnstone, flat roofs are typically found on newer estates where the first extension roofs are now being replaced, and on bungalows with flat-roofed side extensions and dormers. Scotland averages roughly 1,570 mm of rain a year, with the west far wetter than the east, so drainage, falls and wind uplift are part of every specification we write.
How much does a green roof cost in Johnstone?
At Scotland guide rates, a 20 m² insulated extension roof finished as a sedum green roof comes to £4,200–£7,700 including VAT. 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 | £4,200–£7,700 |
| Extension (20 m²), EPDM, new deck + insulation | £2,650–£4,650 |
How is a green roof built on top of a flat roof?
From the bottom up, a green roof is a deck, a waterproofing system with root protection, then drainage, filter, growing medium and plants. The waterproofing does the job of keeping water out. The green layers sit above it.
- Warm roof build-up: vapour control layer, insulation and waterproof membrane on the deck, then the green layers on top. This is the usual choice on a home extension being re-roofed.
- Inverted build-up: waterproofing on the deck, then insulation boards designed to sit above it, then the green layers. This is common on terraces and some commercial roofs.
- Root barrier: roots will exploit any weakness, so the membrane needs to be root-resistant. Some membranes are tested as root-resistant; others need a separate root barrier laid on top.
- Drainage and edges: a drainage layer carries surplus water to outlets, and a gravel or pebble strip is usually left around edges, outlets, upstands and rooflights to keep them clear and accessible.
Upstands still need to rise around 150 mm above the finished surface, which on a green roof means above the top of the growing medium. We check that at the survey, alongside the external fire performance of the build-up where the roof is close to a boundary.
What's included?
- Root-resistant membrane or separate root barrier
- Drainage layer, filter and lightweight growing medium
- Gravel strips kept clear around edges and outlets
- Pre-grown sedum blankets laid and watered in
Building standards in Scotland
In Scotland the building standards technical handbooks (Section 6 for energy) apply, and the council's building standards service decides whether a building warrant is needed. Like-for-like repairs to a roof covering can be exempt; alterations, structural work and new roofs usually need a warrant before work starts. The domestic roof benchmark is 0.12 W/m²K, applied as far as reasonably practicable on an existing roof. More on the rules.
Which nearby areas do we also cover?
Green and sedum roofs in Johnstone: questions
Do you cover Johnstone?
Yes. Johnstone is part of our Renfrewshire coverage, including postcode districts PA5. Surveys and roofs are carried out by vetted roofing teams working under S&K Property Investments and Improvement Ltd.
Who checks building standards for a flat roof in Johnstone?
Where the work needs approval it goes to Renfrewshire Council building standards. 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 Johnstone?
£4,200–£7,700 for a 20 m² insulated extension roof finished as a sedum green roof, at Scotland guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
What happens if a green roof needs repairing?
The green layers are lifted around the problem area, the membrane is repaired, and the layers are relaid. Building on a sound, long-life membrane in the first place keeps that to a minimum.
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.