GRP fibreglass and EPDM rubber roofing are two of the leading flat roofs systems used in the UK market. Choosing the right one can depend on which features matter the most to you. These systems have been built to stand up to the elements for decades. Property owners should thoroughly consider all scenarios when comparing two flat roofing systems like Fibreglass and EPDM to ensure their flat roofs will stand the test of time.  

Before choosing either of them as a flat roofing membrane, one must consider some significant differences. 

What is Fibreglass GRP? 

Known also as glass fiber or GRP (glass reinforced polyester), fibreglass is made up of glass fibres and polyester resin. This material is an excellent waterproofing material and is frequently used on flat roofs. According to BS 6229 and BS 8217, fibreglass roofs are typically classified as flat roofs (defined as having a minimum fall of 1:40 to guarantee a finished fall of 1:80). The term 'fibreglass roof' refers to a flat roof applied with a fibreglass system as a waterproof barrier, typically over OSB3 timber. It consists of a composite laminate painted with a resin topcoat (also called a flow coat or gel coat). 

The main advantage of fibreglass GRP flat roofs is that they can be applied directly to existing roofs. A significant benefit of this approach is the reduction of labour and material costs incurred when replacing the roof structure (namely, the insulation and timber decking). Fibreglass roofing kits come with installation guides designed to assist professionals and DIY installers. 

 Fibreglass (GRP) Roofing Kits 

FiberglassDirect provides a wide range of roofing kits containing all the necessary materials and tools to cover a range of roofs. We also offer a full range of roofing edge trims and supplies 

  • Chopped Strand Matting – available in 450g for light foot traffic or 600g for moderate traffic. Allow 10% extra matting for overlapping.  
  • You can choose between a standard polyester resin or 100% pure polyester resin. 
  • Topcoat for roofing – choose from standard, fire retardant or pigmented 
  • Catalyst (also known as hardener) helps resin and topcoat cure. 
  • Fibreglass bandage to seal edges, corners, and trims 

What is EPDM Rubber Roofing? 

EPDM stands for ethylene propylene diene monomer. As a type of synthetic rubber, it demonstrates excellent waterproofing properties and is commonly used in pond liners and as a flat roofing system. A rubber membrane is used for waterproofing this type of single-ply roofing. The rubber roofing membrane is usually glued to the underlying structure with an adhesive. Installing this type of flat roof is generally relatively quick, though it is not as durable as resin-based Fibreglass systems. 

What is the difference between Fibreglass GRP Roofing and EDPM? 

Ease of Installation 

In both cases, EPDM and Fibreglass Roofing systems are faster to install than other flat roofs or traditional designs, as they are applied cold and are fixed to the property with adhesive or resin rather than heat or flames. Compared to GRP roofing, however, EPDM roofing may take longer to finish due to the various layers that must be applied so the process may be more complicated. EPDM is a sheeted system that relies upon the careful bonding of multiple rolls to the flat roofing surface. Fibreglass requires a level of skill, but many step-by-step guides on how to lay a flat fibreglass roof are available. 


Both EPDM and GRP fibreglass are rated as some of the best flat roofing systems on the market, so quality will not be an issue in either case.   

Weather Resistance 

Both systems exhibit excellent water resistance in laboratory environments. But in reality, fibreglass has a longer and stronger track record of effective waterproofing. Fibreglass roofs are weatherproof, as they feature a fully bonded structure and seamless fabrication, which means moisture cannot penetrate. EPDM is also highly waterproof and does not grow algae, making your home more energy-efficient. In addition, you can use EPDM for other parts of your roofline, such as gutters. Both are resistant to such problems as cracking, blistering, and rot, so your repair bills will decrease if you upgrade to one of these roofs.  

Suitable for foot traffic and equipment placement.  

EPDM is not compatible with foot traffic and equipment placement (e.g. ladders). It is notoriously susceptible to punctures, and in most cases, the punctures are subtle and hard to detect. On the other hand, fibreglass can withstand foot traffic and heavy loads. Fibreglass is therefore favoured over EPDM when the flat roof doubles as an area that will be accessed or experience foot traffic, such as a balcony or room with outdoor seating.  

Puncture resistance 

A common complaint about EPDM is that it's highly susceptible to punctures caused by sharp objects such as gravel (which often gets trapped in shoes), falling debris and equipment like ladders. In addition, EPDM membrane leaks can be notoriously difficult to detect and cost thousands of pounds to fix. By contrast, fibreglass GRP is highly resistant to sharp objects and can be reinforced if necessary.  


With both types of roofing, you can expect long-term durability, and you will usually receive more extended guarantees than traditional felt flat roofs. The GRP fibreglass roof is still one of the most robust systems available, thanks to the fibreglass resin matting and the top layer coating. Together, they form an incredibly tough laminate. When installed properly, fibreglass has consistently been shown to have the longest lifespan of any roofing material. The quality of the EPDM selected plays a significant role in its long-term durability. While both systems are commonly used in the UK for flat roofing, it is essential to understand that the quality of the ingredients, the quality of installation, and the level of care and maintenance provided to the roof ultimately determine its lifespan. 

Ease of repair  

Fibreglass roofs are much easier to repair than EPDM roofs. Because the laminate is fused to the underlying wooden decking, the leak is localised and does not spread. Fibreglass GRP roofs have a very high tensile strength and hardness, so it's virtually impervious to punctures and tears. Also available are instructions for repairing a flat fibreglass roof.  

EPDM roof leaks often leak under the membrane and are challenging to discover but cause significant damage, nonetheless. Because they are glued or mechanically attached to the underlying substrate, they are susceptible to slow but extremely progressive water infiltration; the rainwater can spread undetected under the membrane, leading to extensive damage. Moreover, single-ply leaks are more common since the membrane is more easily punctured.  

Tensile Strength 

Another consideration that can be measured is tensile strength, defined as the amount of force a material can support without fracture when stretched, divided by the original cross-sectional area of the material. EPDM's tensile strength is around 17.5 MPa, while fibreglass's strength reaches up to 78.83 MPa, depending on the type. 


EPDM is the most cost-effective option when you're on a tight budget but still need a high-quality flat roof. It can be true that fibreglass roofing can be more expensive than EPDM; however, this should be balanced with the fact that fibreglass roofing is more robust and long-lasting. Considering its longer lifetime, fibreglass GRP ends up being about half the price of EPDM and less likely to leak.  

Toe work out what Fiberglass roofing kit is suitable for your project, check out the FlatOutCalculator. 

Other flat roofing systems  

The market offers a wide range of flat roofing systems. Among these are felt roofing, modified bitumen, asphalt, and polyurethane. Metal roofs (such as zinc or aluminium) may be more suitable for warehouses and factories. As with EPDM rubber roofs, a felt roof also has drawbacks, specifically that it is UV-sensitive and considered environmentally unfriendly. In some cases, felt roofs contain asbestos as well. They differ from traditional pitched roofs, which are generally constructed of tiles.