EPDM vs GRP

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.

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.

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.

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.

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.