EPDM vs GRP

When it comes to flat roofing, EPDM and GRP are two of the most popular solutions on the market - but which is right for your project? The answer to this isn’t as straightforward as you might think and it depends on several factors including cost, type of roof, exposure to weather, and more. 

Generally speaking, EPDM is a quicker, more affordable choice that's ideal for straightforward flat roofs and green roof builds. 

GRP, on the other hand, is a premium system that delivers a sleek, tough, and seamless finish, making it perfect for complex roof designs with pipes, skylights, or unusual shapes.

In this guide, we’ll break down everything you need to know about EPDM and GRP roofing systems, so you can make an informed decision.
 

Brief overview

We know not everyone has the time to read an in-depth guide, so we’ve written up a brief overview below detailing the pros & cons of each.
 

Understanding the materials

EPDM (ethylene propylene diene monomer) is a synthetic rubber membrane made from ethylene and propylene. It’s known for its flexibility, weather resistance and longevity across many types of flat roofing projects.

It’s incredibly lightweight and easy to install, supplied in large sheets to create a reliable waterproof layer with minimal seams. Its flexibility allows it to expand and contract with temperature changes, reducing the risk of cracking over time.

GRP (glass reinforced plastic) is made from layers of fibreglass matting combined with a liquid resin that hardens into a solid, seamless surface. It’s applied as a liquid and cured, which creates a tough, rigid shell.

Installation

This is where the biggest difference lies.

EPDM

EPDM is known for its quick and straightforward installation. The material comes in large, single-piece sheets that are ideal for simple flat roof applications that don’t require lots of joins or seams.

It’s incredibly easy to install, only requiring an EPDM adhesive and simple roofing tools. Our EPDM rubber roofing tool kit is ideal for this, coming complete with appropriate rollers and paint brushes. 

Because it's flexible and lightweight, fitting EPDM is a job that can be done in as little as a day, which is why it’s one of the most popular solutions for homeowners and contractors.

GRP

GRP installation is more complex and takes longer. Rather than a single sheet, it’s built up in layers using a liquid resin and a reinforcement mat, which are applied directly onto the roof deck.

GRP is particularly useful for complex roof types, like those with pipes or skylights, where there would otherwise be many seams in which if not done correctly could lead to moisture getting in. 

The reason GRP is more difficult to install is that the process requires a perfectly dry surface, the right temperature, and must stay dry throughout the entire curing process. If rain or moisture gets onto the surface before it’s fully cured, it will cause imperfections in the surface like bubbling and poor adhesion, which can lead to moisture getting in. 

Due to the complex nature of GRP, we strongly recommend a professional install it rather than yourself. 
To make installation even easier, we offer complete kits for both EPDM and GRP roofing, coming with everything you need to save time and money.
 

A middle-ground

RESITRIX offers a great middle-ground option between EPDM and GRP. Like EPDM, it’s highly flexible and relatively easy to handle — but instead of relying on adhesives alone, Resitrix uses heat-welded seams for added security and waterproofing. 

This gives it the edge when installing over complex roof shapes or detailing work where standard EPDM might struggle. It's still quicker and more straightforward than installing a full GRP system, but provides extra confidence in tricky areas.
 

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Durability

Both EPDM and GRP are built to last, each with a lifespan up to 30+ years and requiring little maintenance. However, there are some key differences beyond the lifespan.

EPDM

EPDM is highly durable, especially considering how flexible it is. It’s resistant to UV damage, cracking, and weathering, and its flexibility allows it to handle structural movement without tearing. 

However, where EPDM falls short is with heavy foot traffic and vulnerability to punctures from sharp objects. 

GRP

GRP on the other hand is incredibly durable and rigid, being highly resistant to physical damage like impacts, foot traffic, and heavy debris. It’s also less likely to suffer from minor wear and tear compared to flexible systems. 

If you know your roof will be walked over often, GRP will be the best choice for you. 
 

Moisture resistance

Both EPDM and GRP are designed to keep water out — but they handle moisture in slightly different ways.

EPDM

EPDM is naturally waterproof thanks to its rubber composition. Once installed, it forms a seamless membrane that repels water effectively, even in heavy rain or standing water. Its flexibility also helps it stay watertight as it moves with temperature changes, reducing the risk of cracks or splits over time.

EPDM is also better for green roofs, because as mentioned earlier, GRP does not like to be damp and any imperfections will cause issues with leaking. 
The downside is any damage to the membrane, such as a puncture, will cause moisture to get through and will cause damage to your flat roof. 

GRP

GRP creates a completely solid, waterproof barrier once cured. The resin and fibreglass layers bond tightly to the roof deck, creating a seamless, fully watertight surface.

Because it’s rigid and fully bonded, GRP is highly resistant to standing water and heavy rainfall — and when properly installed, moisture penetration is almost impossible.

The key thing to remember is that GRP needs perfectly dry conditions during installation. If moisture gets into the layers before the resin cures, it can weaken the roof's structure. Once fully installed though, it’s one of the most moisture-resistant systems available.

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Weather Resistance (after installation)

EPDM

EPDM offers strong, all-round weather protection. It’s highly flexible, which means it handles expansion and contraction caused by temperature changes without cracking.

It's also resistant to UV rays, ozone, and extreme temperatures, making it a good choice for areas that experience both very hot summers and cold winters. 

EPDM can even stand up to occasional standing water, although heavy, long-term pooling isn't ideal without good drainage.

GRP

GRP provides a hard, rigid, and extremely durable waterproof surface that is excellent at dealing with rain, storms, and high winds. Once fully cured, it is 100% watertight, and its seamless construction leaves no gaps for water to seep in. 

GRP is also UV resistant and performs well in both hot and cold climates, although some surface fading over time is possible without a UV topcoat. Its solid structure also makes it better at resisting physical impacts like hail or falling debris.
 

Repairing/maintenance

EPDM

EPDM roofs are very low maintenance, only requiring checks once or twice a year to remove debris and check for punctures. 
If damage does occur, it’s straightforward to repair. Small tears or holes can often be patched using an EPDM repair kit without needing to replace large sections. This makes EPDM a very forgiving option.

GRP

GRP roofs are extremely durable and generally maintenance-free once installed, meaning there’s very little opportunity for water ingress or weak spots. 
If repairs are needed, usually due to impact damage or aging, the repair process is a bit more involved and will require more time, skill and money compared to repairing EPDM. 

This is because it requires abrading the area, applying fresh resin, and refinishing the surface to match. Our GRP roof repair kit is the best solution for fixing punctures, pinholes and cracks, and can be used across different systems. 

Appearance

EPDM

EPDM is a product that’s not chosen because of its aesthetics - rather it’s practical applications instead. It has a smooth, uniform appearance with a matt grey/black finish which blends in well with most homes. 

If you are installing EPDM, don’t forget to add rubber roof trims - these are the perfect finishing touch and create a sleek, clean edge while adding extra protection to sides. 

GRP

GRP offers a more seamless finish compared to EPDM which can give a modern, professional finish to your roof. While it’s highly UV resistant, some fading can occur after many years without a UV-protective topcoat.

Which is cheaper?

When it comes to upfront costs, EPDM is the more budget-friendly option..

EPDM

EPDM membranes are relatively affordable to buy and install. The material itself is cheaper than GRP, and because the installation is quicker and less labour-intensive, you’ll usually save on labour costs too. 

GRP

GRP is more expensive for both material and installation. The resin, fibreglass matting, and specialist tools required add to the material costs, and because the installation process is more detailed and time-consuming, it will cost more to install as well.

Other deciding factors

Thermal performance

Neither EPDM nor GRP is designed as a thermal insulator by itself. Both systems rely on separate insulation layers beneath the membrane or laminate. However, because GRP forms a fully bonded, rigid surface, it can slightly help with air tightness when properly installed.

The down side of this is if you have a warm deck flat roof, EPDM is slightly breathable so can deal with any moisture build-up in the system and let it out. GRP won't and most GRP systems need a timber deck which in an unvented area isn’t a good idea. For more information on warm deck flat roofing check out this guide here.

Fire ratings

Both EPDM and GRP offer good fire resistance when installed with the correct specifications. EPDM membranes are often manufactured to meet Class BRoof(T4) fire ratings, while GRP systems can achieve similar or higher ratings depending on the topcoat and resins used.
 

Eco-friendly

EPDM is 100% recyclable and has a relatively low environmental impact in production. It also lasts a long time, which means fewer replacements over time.

GRP is less eco-friendly in terms of production, as fibreglass manufacturing is energy-intensive and resin-based materials aren’t recyclable. 

EPDM vs GRP - which is right for your flat roofing project?

If you're looking for a quick, budget-friendly, and eco-friendly solution, EPDM will be the better choice. It’s especially ideal for non-complex small/medium roofs where ease of installation matters.

If you want a professional, high-performance, ultra-durable roof, and you’re willing to pay more for installation, GRP will be the right option, particularly for more complex roofs with pipes or skylights.

If you’re looking for something that bridges the gap between ease of installation and premium performance, RESITRIX is a fantastic option offering the flexibility and straightforward application of EPDM, combined with the added strength and seamless waterproofing of a heat-welded system — making it ideal for both simple and complex roofs. 

If you need any help with your flat roofing project, please feel free to reach out to us today. UKFR is a family-run business with extensive flat roofing knowledge to help you find exactly what you need.

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