Flat RoofingThat Actually Stays Flat— & Watertight
A properly-designed flat roof — correct fall, correct membrane, correct detailing — that sheds water for 20+ years, not one that ponds after every downpour.
Flat Roofing — what, who, when & why
What it is
Full flat-roof installation and replacement in EPDM rubber, GRP fibreglass and high-performance torch-on felt. Extensions, garages, dormers, porches and commercial units.
Who it's for
Homeowners with a failing 1970s–90s felt roof over an extension or garage, self-builders finishing an extension, and landlords maintaining rental portfolios.
When you need it
When you see bubbling, splits, ponding water 24 hours after rain, moss growth on the surface, or damp on the ceiling below.
Why professional matters
Flat roofs fail because of poor falls and poor detailing, not because they are flat. A correctly falled, correctly upstood roof is a 20–25 year asset. A cheap overlay is a two-winter fix.
What happens if you leave it
Damage escalation
- Ponding water accelerates UV degradation and freezes in winter — a small split becomes a full membrane failure.
- Once water is under the membrane, the deck (usually chipboard or OSB) rots quickly and the whole build-up needs stripping.
- Wet insulation loses R-value permanently; you keep paying for heat you don't get.
Common mistakes
- Overlaying a failed felt roof with more felt to defer the cost — traps moisture and doubles the eventual strip-off bill.
- Skipping the perimeter trim upgrade — most flat-roof failures start at the edges, not the middle.
- Choosing the cheapest membrane without checking the manufacturer warranty terms.
How we deliver the work
Inspection
Deck-condition survey, drainage check and measurement — free and without obligation.
Specification
We recommend EPDM, GRP or felt based on span, traffic, upstands and budget, and quote fixed-price in writing.
Strip & deck
Old covering stripped, deck inspected, wet or delaminated boards replaced with 18mm OSB or ply to correct falls.
Install
New membrane bonded or mechanically fixed, upstands correctly formed, edge trims and drips fitted, outlets renewed.
Sign-off
Water-test where practical, walk-around with you, and 10-year HomePro insurance-backed guarantee registered on qualifying full installs.
What you get from booking RTC
20+ year design life
Correctly-specified EPDM and GRP roofs typically outlast three cycles of the felt roofs they replace.
No ponding
Falls corrected during the strip-off, not left to drain to nowhere.
Warm-roof option
Upgrade to a warm-roof build-up during replacement to hit modern U-values and reduce heat loss.
Guarantee that survives insolvency
10-year HomePro insurance-backed guarantee on qualifying installs — you're covered even if we're not.
£5M insured
Public liability and employers' liability at £5M each with Covéa Insurance plc.
Finance available
Flexible finance via iDeal 4 Finance on approved credit.
Materials, methods & specifications
EPDM rubber
Firestone-style single-sheet EPDM — no seams on typical domestic roofs up to 12m span. Bonded to a primed deck with contact adhesive, mechanically clamped at perimeter and outlets. Ideal for garages, extensions and dormers.
GRP fibreglass
Seamless in-situ laminated glass-fibre roofing with pre-formed trims. Excellent for balconies, walked-on terraces and complex shapes. See the dedicated GRP Roofing page for detail.
High-performance torch-on felt
Three-layer torch-applied felt with polyester carrier and mineral cap sheet, still the right specification for larger commercial spans where movement and thermal cycling defeat single-sheet systems.
Falls & drainage
Minimum 1:80 finished fall to outlets, checked with a level during install — not eyeballed. Outlets renewed to match the new membrane.
Warm roof vs cold roof
Warm-roof build-ups place PIR insulation above the deck and eliminate interstitial condensation. Where headroom or eaves detail prevents this, we specify a cold-roof build-up with correct cross-flow ventilation.
Flat Roofing — your questions answered
How long does a modern flat roof last?+
EPDM and GRP roofs installed to specification typically last 20–25+ years. High-performance felt lasts 15–20 years. The 1970s pour-and-roll felt many people are replacing lasted 8–12.
How much does a flat roof cost?+
A single-garage EPDM replacement is priced on a fixed, itemised written quote after a free inspection — every job varies by pitch, access, materials and scope. A large extension in GRP is priced on a fixed, itemised written quote after a free inspection — every job varies by pitch, access, materials and scope. Every quote is fixed-price and itemised.
Can you replace my roof in one day?+
A single garage in dry weather — yes. Extensions and complex roofs are 2–4 days depending on upstand detail and roof lantern presence.
Do I have to strip the old roof?+
Almost always, yes. Overlays trap moisture, hide deck rot and void most manufacturer warranties. We only overlay where the existing deck and membrane are demonstrably sound.
What guarantee do you offer?+
10-year HomePro insurance-backed guarantee on qualifying full installations, plus manufacturer product warranties.
Will the new roof match the height of my extension?+
Yes — a warm-roof upgrade typically raises finished level by 100–140mm, allowed for in the design and detailed at upstands and abutments before quoting.
Are you insured?+
£5M public liability and £5M employers' liability with Covéa Insurance plc.
Do you provide emergency flat-roof repairs?+
Yes — for splits and active leaks, call 07722 733343 for a same or next-day make-safe.
GRP Roofing
Seamless fibreglass roofs — durable, guaranteed, no seams.
Learn moreRoof Repairs
Fast, honest repairs — slipped slates to storm damage.
Learn moreRe-Roofing
Pitched & flat full replacements with 10-year guarantee.
Learn moreGet a free, fixed-price quote for flat roofing
Free inspection, itemised written quote, 10-year insurance-backed guarantee on qualifying installs. No pressure, no call-out charge.
TrustMark · Fair Trades 9.5/10 · HomePro · £5M insured
Tell us about your roof
Get Your Free Fixed-Price Quote
Free inspection, no obligation. Response within one working day.