Why Flat Roofs Fail (And How To Fix Them Properly)
Most flat roofs in Leicestershire are on garages, single-storey rear extensions, dormers, bay windows and porches. The vast majority were originally built in bituminous felt — usually three layers of pour-and-roll felt over a timber deck — and have a working life of around 15-20 years before the felt cracks, the laps fail, and water finds its way in. By the time you see a damp patch on the ceiling below, the felt has usually been failing for several years and the deck underneath is often saturated.
When a flat roof gets to that stage, patch repairs almost never solve the problem long-term. The felt is at end of life, the deck wants checking and probably partly replacing, the upstand details are usually wrong by modern standards, and there's normally no insulation worth the name. A full strip-and-replace with a modern system is almost always cheaper over a 20-year horizon than chasing leaks every winter.
EPDM Rubber — Our Most Common Choice
For domestic flat roofs in good shape underneath, single-ply EPDM rubber from Firestone or Classicbond is the system we install most often. It comes in single sheets up to 15m wide, so a typical garage or extension roof is covered in one piece with no joints anywhere in the field of the roof — the only joints are at the perimeter and around penetrations, and these are bonded with butyl seam tape rated for 50+ year life.
EPDM is fully bonded to the deck with cold adhesive (no torches, no flame), it stays flexible at -40°C and up to +120°C, and it has a service life of 25-50 years depending on the system specification. The Firestone RubberCover system carries a 20-year material warranty; the upgraded Firestone Bonded membrane carries 25 years. We hold the installer accreditation needed to issue these warranties.
GRP, Torch-On Felt & Liquid Systems
GRP fibreglass is a hand-laminated system — resin and glass matting are applied directly to a plywood deck and finished with a pigmented topcoat. The result is a hard, glossy, fully bonded waterproof shell with no joints anywhere. Particularly good on roofs that get foot traffic (balconies, walk-on terraces).
SBS-modified torch-on felt is the modern descendant of the old pour-and-roll bitumen felts — better polymer chemistry, longer life, and properly engineered laps that don't fail in five years. We use it where a felt-on-felt repair is genuinely warranted or on traditional buildings where the visual continuity of a felt finish matters.
Liquid waterproofing — Kemperol, Sika Liquid Plastics, Triflex — is the right choice for roofs with complex penetrations, valley gutters, balcony detailing, or where the building can't be taken out of use.
Insulation Upgrades At The Same Time
Modern Building Regulations require U-value 0.18 W/m²K on a replacement flat roof, which typically means 100-150mm PIR insulation on top of the existing deck (a warm roof build-up). It usually makes sense to upgrade the insulation while the covering is being replaced — the access is already there, the cost difference is modest, and the energy saving over the next 25 years pays back several times over.
On garage roofs where the space below is unheated, this isn't required. On habitable extensions and dormers where the room is heated, it is required by Building Regs and we include it in the quote by default.
Frequently Asked Questions
Can you patch a flat roof or does it need replacing?
Patches work as a short-term fix on a roof that's basically sound but has localised damage. On a roof where the felt is generally crazed, brittle and lifting, patches are throwing money away. We'll be straight with you about which yours is.
How long should a flat roof last?
EPDM: 25-50 years. GRP: 25-30 years. Modern SBS torch-on felt: 20-25 years. Liquid systems: 20-25 years. Old bitumen pour-and-roll felts (1980s-90s): typically 15-20 years and many are now well past their date.
Will you replace the deck underneath?
Wet, soft or rotten deck always gets replaced. We lift the existing covering, check the deck thoroughly, replace any compromised areas with new 18mm WBP plywood or OSB, and then install the new waterproofing onto a sound substrate.
Can I add insulation at the same time?
Yes — and it usually makes sense to. Modern Building Regulations require U-value 0.18 W/m²K on a replacement flat roof. We include this in the quote whenever the existing roof is being fully replaced on a heated structure.
How much does a new flat roof cost?
A typical garage roof in EPDM is usually £1,800-£3,200 fitted. A single-storey extension is £2,500-£5,500 depending on size. Free written quotes after a site visit — no call-out charge.