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)
What makes a good extension roof in Johnstone?
If you're fitting a new kitchen under an extension in Johnstone, that's a good time to replace the roof. It makes sense to rebuild the roof before fitting new units, ceilings and lighting below, and the insulation upgrade makes the room more comfortable all year.
In and around Johnstone, flat roofs are typically found on low-rise post-war blocks of flats, and on lock-up garage blocks on estates. 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 new extension roof cost in Johnstone?
Guide price in Johnstone: £2,650–£4,650 for a 20 m² extension roof in EPDM with a new deck and insulation, including VAT at Scotland rates. The fixed price comes after a free survey for new and replacement roofs.
| Job | Guide price inc VAT |
|---|---|
| Extension (20 m²), EPDM, new deck + insulation | £2,650–£4,650 |
| Extension (20 m²), GRP, new deck + insulation | £2,850–£5,100 |
| Extension (20 m²), EPDM, insulation + 1 rooflight upstand | £2,850–£4,950 |
| Single garage (18 m²), EPDM rubber | £1,500–£2,650 |
Why does water pond or leak where the extension meets the house?
Usually because the fall runs the wrong way, the abutment detail has failed, or the roof has sagged close to the wall. The junction with the house is the most common leak point on an extension roof.
If the roof falls towards the house, or the deck dips near the wall, water sits against the upstand and finds any weakness in the flashing above. Older roofs often have the felt simply turned up the brickwork with no cover flashing, or a flashing that has pulled out of its joint. A patch will not change a fall. We re-firr or use tapered insulation so water runs away from the wall, then form a new upstand, usually 150 mm above the finished roof, with a flashing chased into the mortar joint.
Rooflights and lanterns are the other weak point. A lantern needs a properly built kerb with the membrane dressed up and under its frame. We rebuild rooflight upstands within the roof job; we do not supply the lantern itself. Our guide to ponding water explains the causes in more depth.
What's included?
- Falls set away from the house wall
- Free survey of the roof, abutment and room below
- New abutment upstand and flashing, plus rebuilt rooflight kerbs
- New deck, vapour control layer and warm-roof insulation
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?
Extension and kitchen 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 new extension roof cost in Johnstone?
£2,650–£4,650 for a 20 m² extension roof in EPDM with a new deck and insulation, at Scotland guide rates including VAT. The fixed price comes after a free survey for new and replacement roofs.
Can you keep my existing roof lantern?
Often, if the lantern itself is sound. We lift it, rebuild the kerb, dress the new membrane up the upstand and refit the lantern.
Why does my extension ceiling get damp in winter if the roof isn't leaking?
That is often condensation in a cold roof, where warm, moist air reaches the cold underside of the deck. A warm-roof replacement with a vapour control layer usually solves it.