Three flat roofing systems account for the vast majority of work we carry out on Ipswich extensions, garages and outbuildings: GRP fibreglass, EPDM rubber membrane, and various types of felt. They differ significantly in cost, lifespan, installation requirements and suitability for different applications. This guide gives you the information you need to make an informed decision when your flat roof needs replacing.
GRP (glass reinforced polyester) is our standard recommendation for most domestic flat roofing applications in Ipswich. It is a seamless system — the laminate is laid wet and cures to form a continuous surface with no joints. Joints are the weak point in any waterproofing system; removing them removes the primary failure mode. Design life with correct installation: 25 years or more.
GRP handles the East Anglian thermal cycle well. The material expands and contracts slightly with temperature change, and the glass fibre reinforcement gives it the flexibility to do this without cracking — provided the deck beneath it is stable. On a sound, correctly ventilated deck, GRP performs reliably. On a soft deck or one with inadequate ventilation, it will fail earlier. We check deck condition as standard on every survey and include deck replacement in the quote where it's needed.
The limitation of GRP: it requires specific installation conditions. Below approximately 5°C, the resin cures slowly and the result is compromised. In very hot conditions (above 25°C), it cures too fast. This means GRP installation has a preferred temperature window, and in Ipswich's variable climate we schedule accordingly.
A correctly installed GRP (glass reinforced polyester) roofing system carries a typical service life in excess of 25 years, subject to correct deck preparation and resin curing.BS 6229 and GRP manufacturer system specifications
EPDM is a synthetic rubber membrane — a single sheet laid over the deck and adhered at the edges. It handles temperature extremes well (better than GRP), is more forgiving of imperfect deck conditions, and is cost-effective for larger simple areas. Design life: 20+ years.
EPDM is our recommendation for larger flat areas — outbuildings, flat roofed garage ranges, larger commercial applications — where the cost advantage of EPDM over GRP on a simple square area is significant. For smaller, more complex shapes with multiple penetrations (pipes, outlets, upstands), GRP's seamless application is superior.
The limitation of EPDM: the joins between sheets and the edge detailing are the potential failure points, as with any lap-jointed system. On larger simple areas with few joins, this is not a significant concern. On complex roofs with many features, GRP's seamless nature is a meaningful advantage.
Modern torch-on felt (SBS modified bitumen) is a significant improvement over the original cold-applied bitumen felt systems installed on most 1960s–80s Ipswich extensions. Torch-on felt, properly installed in multiple layers with correct laps, has a design life of 15–20 years and performs adequately on simpler applications. It is the lowest-cost option upfront.
Original single-layer cold-applied felt, which is what most Ipswich extension flat roofs carry from the 1960s–80s, has a design life of 10–15 years. On properties where this original felt has been on the roof for 30–40 years, we are almost always dealing with a failed system. We do not re-felt with single-layer systems; where felt is the specified system, we use multi-layer torch-on.
For rear extensions and integral garages: GRP fibreglass. Seamless, durable, handles the East Anglian climate well, and the 25-year design life makes it the best long-term value for standard domestic applications in Ipswich. For larger outbuilding roofs where cost matters and the shape is simple: EPDM. For tight budget situations where a 15-year solution is acceptable: multi-layer torch-on felt.
GRP for most garage applications — seamless construction is ideal for the typical garage roof with multiple penetrations and a gutter outlet. EPDM is cost-effective on larger, simpler areas. We recommend after surveying the specific roof.
GRP: £60–£90 per m². EPDM: £50–£75 per m². Torch-on felt: £35–£55 per m². For a 20m² garage roof the difference is approximately £200–£500 between systems.
GRP: 25 years+. EPDM: 20 years. Torch-on felt: 15 years. Original 1970s single-layer felt: likely at or past end of life if not replaced in the last 15 years.
We don't install GRP below approximately 5°C — it affects the cure quality. In Ipswich's climate this means winter installation may need to be scheduled for milder periods. EPDM and torch-on felt are less temperature-sensitive.
Original 1960s–80s cold-applied bitumen felt was a single layer with a 10–15 year design life. At 30–50 years old, it has been past its design life for decades. Nothing went wrong specifically — it simply ran its course. Modern systems are significantly better specified.
We check deck condition as standard on every survey. If the deck has softened from slow water ingress — very common on Ipswich properties where the felt has been failing gradually — we replace it as part of the job. This is included in our survey quotes, not added as a surprise on the day.
Only if the existing deck is completely sound. In most cases we remove the old felt to check deck condition properly. Over-laying without checking the deck is a shortcut that causes early GRP failure.
Whatever your roofing question, we're happy to help. Call us for a free survey and honest assessment.
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