📋 Roofing guide
The choice of flat roofing material has a significant impact on how long the installation lasts and how much maintenance it requires. Here is an honest comparison of the three principal systems.
Flat roof technology has advanced considerably over the past two decades. The bitumen felt that was the only realistic option for garage roofs and extensions until the 1990s has been joined by GRP fibreglass and EPDM rubber — systems that outperform traditional felt in almost every respect. Understanding the differences between them helps you make an informed decision rather than simply accepting whatever a roofer proposes.
Bitumen felt is the original flat roofing material and remains the most widely recognised, if not the most widely used for new installations. It is laid in multiple overlapping layers, with each layer bonded to the one below using heat (torch-on felt) or cold adhesive (the older and less reliable cold-pour method).
Traditional cold-pour felt: 10 to 15 years. Modern torch-on felt: 15 to 20 years. The overlapping seams between layers and at edges are the primary failure points.
The lowest upfront cost of the three systems. However, when the shorter lifespan is factored in, the cost over a 25-year period is typically higher than GRP or EPDM.
Felt requires periodic inspection and is more vulnerable to puncture and UV degradation than modern systems. Repairs are relatively straightforward when caught early.
Lower-budget applications, or repairs to existing felt systems where the deck is sound and full replacement is not yet warranted. We install torch-on felt where it is the right choice for the application.
GRP (glass reinforced plastic) fibreglass flat roofing is installed as a two-coat liquid system. A fibreglass matting layer is saturated with resin and laid onto the deck, followed by a coloured topcoat once the base coat has cured. The result is a single, seamless, hard membrane that is chemically bonded to the deck.
The absence of seams is the key characteristic of GRP. Every seam on a traditional felt roof is a potential failure point. A GRP roof has none — the entire surface from edge to edge, around upstands and across corners, is a single continuous membrane. There is nowhere for water to find a way through except at the edge details, which are where the quality of installation is most critical.
25 years or more when correctly installed. The system is used in marine applications and is highly resistant to UV, weathering and physical impact.
Moderate upfront cost — more than felt, less than high-specification EPDM on larger areas. The longer lifespan makes it the most cost-effective option for most domestic applications over a 25-year period.
Essentially maintenance-free once installed. The hard surface can be walked on for cleaning and maintenance access. Repairs, if ever needed, are straightforward using the same materials.
Garage roofs, rear extensions, bay tops and most domestic flat roof applications. The seamless nature makes it particularly well-suited to roofs with complex shapes or multiple upstands.
GRP requires specific installation skills and materials. A GRP roof installed by someone without the right training or using the wrong resin-to-catalyst ratio will fail prematurely. We have been installing GRP for many years and carry the correct materials and equipment for every job.
EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane supplied in large rolls and bonded to the deck using contact adhesive. Like GRP, it is a single-membrane system — the large roll sizes mean fewer seams than traditional felt, though EPDM installations do typically have seams at joints between rolls and at upstands, unlike the truly seamless GRP system.
25 to 30 years when correctly installed. EPDM has a proven track record in commercial roofing and has been used in the UK for several decades.
EPDM handles thermal movement exceptionally well. The rubber membrane expands and contracts with temperature changes without cracking, making it particularly well-suited to larger flat roof areas where thermal stress is a greater factor.
Similar to GRP for smaller areas. On larger flat roofs, EPDM can be more cost-effective than GRP due to the speed of installation with large roll sizes.
Larger flat roof areas, or applications where thermal movement is a particular concern. An excellent alternative to GRP where the specific characteristics of the building make it the better choice.
For most domestic flat roof applications in Merseyside — garage roofs, rear extensions and bay tops — we recommend GRP fibreglass as our first choice. The seamless installation, hard-wearing surface and 25+ year lifespan make it the best value option for the majority of jobs we quote.
For larger flat roof areas, or where the specific characteristics of the property or its location make EPDM the better choice, we install EPDM instead. We carry both systems and make our recommendation after assessing the specific roof rather than defaulting to one system for every job.
Traditional felt remains a valid option for repairs to existing felt systems and for lower-budget applications where the deck is sound. We will always tell you honestly which approach is most appropriate for your specific situation.
If your flat roof is leaking or deteriorating, call us on 07596 884288. We inspect the deck, assess the existing system and recommend the most appropriate replacement. Written quote before any work begins.
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