EPDM vs GRP: Which Is the Better Roofing System?

When it comes to flat roof installations, options are many. From TPO to EPDM to PVC and GRP (Glass reinforced polyester). Each material has its pros, cons, and ideal use cases and what you pick will be determined by factors such as climate budget, and expected impact.

In this blog we pit EPDM against GRP to find out which of the two is better for flat roofs.

What is GRP roofing?

GRP roofing is a flat roofing system used to build weather-proof flat roofs that often last for over 25 years.

GRP or Glass reinforced polyester is a composite material, consisting of polyester resin which is reinforced with glass fiber, specifically  CSM (chopped strand mat glass fiber). This is why it’s also called fiberglass roofing. GRP is a lightweight but strong product due to the reinforcing fibers. 

The resin comes packaged in drums while the glass fiber comes in rolls from 1m wide and can accommodate large areas with rolls from 10m² to 120m². The fiberglass rolls come in varying thicknesses including 225g, 450g, and 600g.

GRP coating is cold applied (no heat is used) and provides a joint free roof surface since  the liquid is spread evenly. The result is a uniform, durable and UV resistant coating. GRP is well suited for complex roof shapes because the material can easily be molded around structures. 

Properties of GRP

Good strength-to-weight ratio – GRP roofing doesn’t need to have a lot of material in order for it to be strong.

Flexible – The physical properties of GRP allow it to be molded into different shapes and around corners and crevices.

Corrosion resistant – GRP has great corrosion resistance, making it suitable for use in areas such as factories and commercial buildings.

Lightweight – This makes it easy to transport and carry during installation.

Non-conductive

What is EPDM flat roofing?

EPDM, stands for Ethylene Propylene Diene Monomer, is a type of synthetic rubber made from ethylene and propylene. It is used in many different industries to make items such as gaskets, car window linings, tubing, and of course roofing.

As roofing, EPDM is available in black and white. White EPDM roofing is preferred in cases where higher reflectivity is desired. White roofing reflects more heat away, reducing air conditioning costs.

EPDM is produced in various thicknesses – 0.045, 0.06, and 0.09 inches. Most contractors use the industry standard of 0.06 inches, which is very close to the thickness of a quarter.

Different manufacturers of EPDM produce different variations of the material, to be used with various adhesives and application procedures. For example some EPDM sheets come attached with fleece material on the back side, which supposedly increases its strength and helps to distribute tension across the roofing. Another kind comes with a sticky back and is reinforced with fiberglass strips. However, despite the variations, they are all still EPDM and therefore exhibit largely the same behavior.

EPDM roofing membrane also comes in a variety of widths ranging from 7.5 to 50 feet. Sizes include:

• 1-meter wide and 10-meter long strips
• 3-meter wide by 15 meters long
• Some types of EPDM, such as the basic plain version, can be cut to the exact size of the roof, say, 20M X 20M.

Properties of EPDM 

• Resistant to high temperatures
• Adaptable to low temperatures
• UV resistant
• Waterproof
• Steam resistant
• Resistant to weathering – However, prolonged exposure to extreme weather such as hail, wind, snow or sub-zero freezing temperatures will negatively impact the lifespan of your EPDM roof.
• Flexible – 600% elongation and a tensile range of 500-2500 psi

EPDM vs GRP: A Comparison

Material Quality

EPDM is a high quality synthetic rubber that is resistant to weather, solvents, ozone, among other things. However it is relatively easy to puncture as compared to other roofing materials. 

GRP – GRP is very lightweight but still very strong. It is ideal for roofs that carry heavy equipment. GRP roofs are seamless, making sure no air or water flows under the roof. 

Durability & Lifespan

EPDM – When installed properly, EPDM lasts longer than other roofing systems. Its average lifespan is 25-30 years and can even reach 50 years with the right care and maintenance. The elasticity of this synthetic rubber allows it to expand and contract depending on the outside temperature, thereby preventing cracks and blisters. 

However, though EPDM is quite robust, it is not ideal in roofs where there is bulky moving equipment or heavy foot traffic as it can tear easily under such circumstances. 

It is the same case with GRP. With correct installation, GRP roofing also offers good durability with an average lifespan of at least 25-30 years. Despite its lightweight, GRP possesses great load-bearing performance due to its good strength-to-weight ratio. GRP can withstand harsh conditions and heavy use.

Weather Resistance

EPDM roofing is highly waterproof and therefore prevents water leakages quite well. It is also resistant to UV and extreme temperatures. EPDM has special resistance to salt water and corrosion – EPDM is highly waterproof and seam-free which means it is much less likely to cause leakages. Plus, with special resistance to salt water, it is a good choice of flat roofing for coastal properties.

GRP – GRP is also highly waterproof and therefore perfect for stormy climates. When properly installed, it is completely leak-proof and watertight so even the heaviest rains won’t be an issue. 

GRP roofs are also UV resistant but can fade after a few years of continuous exposure to the sun.

Installation

EPDM – EPDM installation is relatively easy for experienced contractors. It is a flame-free application and is applied as a single rubber sheet glued to the roof decking using a wet bonding adhesive. Trims are then applied to the corners and edges to create a durable and waterproof finish. Although straightforward, it is important to only hire contractors with good EPDM work under their belt because poor installation leads to problems such as mold, leakages, tears, and other costly situations.

GRP – GRP is also fairly straightforward to install. It involves pouring a layer of resin, then placing a mat of fiberglass strands and then a second layer of the resin. A catalyst is added to the resin to make it dry faster. To increase weather resistance, a protective topcoat is then applied.

Because of pouring and drying times, GRP roofing can take longer to install. It also can’t be installed in wet conditions since water will upset the resin mixture.  Additionally, it is also not ideal for larger roof areas because expansion rates can be excessive.

Appearance

EPDM – EPDM popularity is definitely more because of its practicality rather than its visual appeal. It offers a simple all-black or all-white cover. This simplistic look may be the reason why it’s more popular in commercial applications than residential applications..

GRP – GRP roofing also provides a simplistic look. It is a seamless, clean roof finish but the fiberglass color can be adjusted depending on your preference. 

Sustainability

EPDM – EPDM is the more eco-friendly roofing system as it is partly developed using recycled rubber, thanks to a 2006 initiative by the EPDM Roofing Association. 

EPDM rubber, unlike TPO and some other roofing materials, does not contain leaching chemicals that pollute water bodies. This property also makes it ideal roofing if you plant to harvest rainwater. EPDM also doesn’t contain bitumen and has a low smog impact. EPDM roofing is also suitable for use with solar panels, which are easy to install on EPDM roofs. 

GRP – GRP is also relatively eco-friendly from the fact that much less energy is used in its production in comparison to other roofing materials. GRP roofs also do not emit harmful substances so they are safe to use in greywater systems. GRP is also quite long-lasting so waste arising from constant 

Cost

EPDM – As EPDM is partially made using recycled materials, it is generally on the more affordable side of roofing systems. Although initial cost is higher than that of felt roofing for instance, EPDM roofing is very durable so once installed, you will not incur the cost of regular replacements and fixes.

The installation process is also pretty simple, no need for highly specialized equipment and personnel, which makes for an affordable installation. 

GRP – GRP roofing is generally more expensive than EPDM since it utilizes more premium materials such as fiberglass mats. The installation process of GPR is more complex in terms of time and equipment but due to its durability, subsequent repair costs will be low. 

Pros and Cons of EPDM roofing

Pros of EPDM as roofing	Cons of EPDM as roofing
Durable and low maintenance – EPDM roofing membranes are made of a unique synthetic elastomer rubber that has various desirable properties such as resistance to UV rays and extreme temperatures. The synthetic rubber also doesn’t support the growth of moss.	Tricky installation – The most common reason for failure of all roofing systems, not just EPDM roofing, is poor installation. With EPDM, proper installation is even more because it is thinner than other membranes like modified bitumen. Proper measures include installers using foot mats to prevent tears to the EPDM sheets during installation.
Relatively more eco-friendly – Compared to other roofing systems such as TPO, EPDM roofing may be more eco-friendly because old EPDM roofing is diverted from the landfill route to be reused and recycled.	Requires typically flat roof deck – As opposed to modified bitumen which can be applied over slight bumps and raises, EPDM is best placed on flat surfaces.
Custom sizes – With EPDM roofing membranes, you can contact your manufacturer to get sheets that fit your roofs exact dimensions. This helps to reduce seams which is always a good thing in roofing because it means there are less potential points of failure or leaking.
Reduce air conditioning costs – The black EPDM absorbs heat, reducing heating costs. White EPDM on the other hand reflects heat away, preventing overheating in the building and reducing cooling costs.
Easy and cheap repair – Repairs typically involve cleaning the damaged area, then applying new adhesive or flashing tape.

Pros and Cons of GRP roofing

Pros of GRP	Cons of GRP
Low Maintenance.	More expensive
Possibility of integrated insulation to reduce heat loss	PNot well suited to large roofs because it had high expansion rates
Quick and easy handling and installation

So which is best, EPDM or GRP?

It all depends on your circumstances. For a wet stormy climate or a roof with lots of foot traffic, GRP may be the best option. For areas with varying weather and not a lot of roof activity, EPDM is ideal. Visit our collections to view the best rubber surfacing products, including top-of-the-line EPDM.