What is EPDM?

In this article we’ll look at answers to some common queries about EPDM: 

What does EPDM stand for? 

First of all, EPDM stands for Ethylene Propylene Diene Monomer. It’s a type of synthetic rubber made up of ethylene, propylene and a covalent component that contains two double bonds called a diene. This enables cross linking via sulphur vulcanisation. When combined this creates a rubber that has a higher resistance to heat, light and the effects of UV light than normal rubber. It’s commonly used in rubber roofing supplies created by brands such as Classic Bond, Resitrix and Firestone Roofing.  

Where can EPDM be used? 

You can use EPDM rubber membranes to cover roofs that are either flat or have a low slope (check the suitable roof angle of any EPDM product before you purchase as this may vary). EPDM rubber roof membranes are great for garage roofs, sheds, extensions, garden offices, green roofs, orangeries and dormer window roofs. You can also purchase EPDM gutter liner kits that can be used on most types of gutters. These gutter liners are just as resilient as the EPDM rubber roofing material and will prevent any leaks from occurring across their 50-year lifespan.  

EPDM is suitable for covering almost any flat roof. You can even use EPDM to top-up existing flat roofs. Products such as DuoPly Fleece Reinforced EPDM can be applied straight on top of an old flat roof without the need to remove the old material first. The Duoply has been produced with a fleece lining which is designed to cover any small ridges or cracks that may be present in the existing roof without affecting the new EPDM layer. DuoPly Fleece Reinforced EPDM can also be used below a green roof system, providing a strong, durable base. 

How long does EPDM last? 

EPDM is recognised as one of the most durable roofing materials that you can use on a flat roof. It’s an incredibly resilient material which will withstand both the heat and UV rays of the sun. It’s also highly resistant to damage due to the cold or freezing temperatures. Classic Bond, a leading manufacturer of EPDM rubber membranes and gutter lining kits are proud to say that their membranes are still going strong after 50 years of use on some structures, with many of their products having a life expectancy of 50 years.   

Is EPDM waterproof? 

EPDM is completely water resistant, and will protect your structure from driving rain, hail, sleet and snow. Classic Bond’s EPDM membrane is also 14% thicker than many other brands making it even more resistant! 

EPDM can usually be installed in one large sheet, eliminating any seams. This makes installation super easy, as well as giving your new rubber roof a cleaner appearance. But above all, it also provides unrivalled water resistance as there is no risk of leaks around the seams, which is a common risk when more than one sheet has been used. 

Is EPDM affected by moss or algae? 

Classic Bond state that their EPDM does not support moss or algae growth making it an incredibly low maintenance, long lasting product. 

Can You Walk on EPDM? 

EPDM roofing membranes can typically withstand a certain amount of footfall for cleaning or during installation. It is advised however to take as much care as possible and to spread any weight as evenly across the roof as you can. If you need to place a ladder on an EPDM roof for example, place it on a board to spread the weight evenly.  
Other materials are available to purchase that will give your EPDM roof added stability and support. These include balcony tiles, slab supports and more. 

Is EPDM eco-friendly? 

Yes, EPDM is considered an eco-friendly product, as it requires less energy to produce than many alternative membranes. Manufacturers are also increasingly using material from recycled tyres to produce it. And, once you are finished with your EPDM roof it is also 100% recyclable. 

Another advantage of EPDM is that it won’t contaminate roof water. This means you can collect rainwater from your roof for use around the garden.  

How Do You Install EPDM? 

Firstly, it’s best not to install an EPDM roof during cold weather because it won’t be as easy to shape and work with. If you have to however, try to purchase EPDM that isn’t folded. 

1. Clean the roof surface prior to installation, otherwise the glue may not work as effectively. You may choose to install a completely new roof decking using OSD board or plywood. Or alternatively, you can overboard a roof by installing OSB or plywood on top of the original roofing. Although, as mentioned previously, some EPDM membranes such as the DuoPly Fleece Reinforced EPDM are designed to go on top of old roof coverings. Make sure that you check the product information thoroughly when choosing your EPDM membrane. 
   
   
2. If your membrane was folded when you bought it, unfold it and lay it out flat on your roof and then wait for 20 minutes. This will allow the membrane to relax, which will prevent it wrinkling or having any creases when installed onto the roof.  
   
   
3. After 20 minutes check your membrane. If it’s bigger than the area that you need to cover, (be sure to allow some overhang for securing and for applying flashing and trims however) trim it to a workable size using a knife or sharp scissors. 
   
   
4. If you’re using a water-based adhesive, fold back half of your membrane and apply the adhesive to the roof decking using a roller for even coverage. Remember that any lumps or bumps will show once the membrane is laid down so try to keep this as smooth as possible. Leave a gap of approximately 6 inches around the edges, including around upstands, for the contact adhesive to be applied. 
   
   
5. Roll out the membrane from the middle outwards, smoothing it out and ensuring that no creases form. 
   
   
6. Using a dry bristle brush, rub over the top of the membrane to make sure that it’s smooth and every part of it is in contact with the adhesive. 
   
   
7. Repeat steps 5 to 7 with the other side of the membrane. 
   
   
8. Apply the contact adhesive to the areas that you left around the edges and around any upstands using a roller. This time apply it to both the boarding and the bottom side of the membrane. Lay the edges down, again making sure that it has full contact with the glue and the boarded surface ideally using a silicone roller which is firmer than a brush. 
   
   
9. Apply any flashings or trims (see more information below). Then trim the membrane further as needed to achieve a perfect fit. 

For a more detailed explanation prior to application, always refer to your products’ installer’s guidelines. 

How to Fit EPDM Flashing 

If your flat roof sits against a vertical wall you may also want to apply EPDM flashing to prevent water ingress. This should be done at the same time as applying the membrane. You’ll need to make sure that you have enough excess membrane for it to sit up against the adjacent wall at least 150mm and then sit into the chase. 

1. Using a multi chisel or an angle grinder, chase out a horizontal line in the wall that’s at least 25mm deep and 150mm above the deck. 
   
   
2. Whilst you are laying your EPDM membrane ensure that there is enough to run up to the chase. Cut off any excess material using a sharp knife, making sure that when you cut the membrane off at the corners you cut vertically or at an angle.  
   
   
3. Apply the contact adhesive to the membrane and fix it into place against the wall. 
   
   
4. You may want to apply EPDM tape to the external corner where the membrane abuts the wall. 
   
   
5. Fix the wall trim/flashing into the chase. 
   
   
6. Using a 7mm masonry drill make a hole through the wall trim into the wall behind it for the wall plugs, one at each end and one in the middle. 
   
   
7. Screw the perimeter fasteners into the wall plugs using the hex bit and drill. 
   
   
8. To finish, apply a lap sealant above the top of the trim along the line of the chase. 

The above is just a guideline, and the actual process may vary depending on the type of flashing and product(s) you use. For example, a Gutter Drip trim will also require a baton and back plate fixing. Always refer to the product’s installation guide. 

How Do You Maintain EPDM? 

Because EPDM doesn’t support the growth of mould, moss or algae; you should find that your new roof requires very little maintenance. It is a good idea however to check your flat roof a few times a year for any debris which can be gently brushed off. 

EPDM vs Felt or GRP Roofing 

When it comes to choosing a membrane for your flat roof you have a number of options including EPDM, Felt or GRP. 

A felt roof is often attractive because of its low price point. However, bear in mind that a felt roof needs to be welded during the installation process and therefore must be installed by a contractor. Felt is also less resilient than EPDM and does not perform well during hot temperatures, when it can become brittle and easily damaged by footfall. It’s also less resistant to ripping or tearing than an EPDM roof and although patch repairs can be made, they can make your roof look messy. In addition, the overall life expectancy of a felt roof is only 15-20 years compared to 50 years with an EPDM roof. 

GRP stands for Glass Reinforced Plastic, also known as Fibre Glass. It has numerous advantages, including being both strong and lightweight, as well as visually attractive. GRP roofing however needs to be installed by a professional, and is more expensive in general than EPDM rubber. 

An EPDM roof is incredibly resistant and it won’t blister or peel due to direct sunlight. It also has a comparatively low price point, and can be installed by a confident DIYer – saving you money on hiring a contractor. One EPDM roofing’s biggest advantages is that it’s available in one large sheet. This means the roof is much easier to install, and without seams or patches; the finished roof looks far neater. And of course, fewer seams also means there’s a much lower chance of water ingress – giving you a roof that’s far more resilient all-round.  

How Much Does EPDM Cost? 

You can expect to pay from £9.20 per square metre for a cut-to-size EPDM rubber membrane. There are several other options available including self-adhesive membranes which make installation much quicker and easier. Prices for these start at £91.92 for 10m by 0.33m, with many other sizes available. There is also the option to buy a kit that comes complete with everything that you’ll need for the installation process. This will include the adhesive and bonding sealant for the edges. Kits start at £46.28 for a 1.4m by 2.14m membrane and go up to £253.70 for a 4.2 by 5m sized membrane. 

How to Choose EPDM Trimming 

When choosing your EPDM membrane, you’ll find that there are a number of different trims available and they each have a different use: 

Gutter Drip Trim 

A gutter drip trim is added to the side of the building. It overlaps and holds the membrane securely in place, and provides protection as a step down to the gutter. This means water can flow easily with no risk of ingress. Many gutter drip trims come complete with a back plate which should be secured onto a wooden baton. The membrane then goes over it and the Gutter Trim goes on top. You will also need Corner Drips to go with this (see below). 

Corner Drip 

You can get both external and external Corner Drips, depending on the corner you need them for. They’re used to join two Gutter Trims together. They’re easy to install, simply by supergluing one side and pressing firmly into place. Do always make sure to follow the specific guidelines provided for your product as these can differ. 

Kerb Edge Trim 

A Kerb Edge Kerb Trim is used when a gutter isn't present and simply sits on top of the membrane to add extra reinforcement. It also eliminates the need for a timber upstand, and is used on the fascia edge of the roof. 

Corner Kerb 

This is used where two Kerb Edges meet at the corner, again you can purchase internal or external corner kerbs, dependent on the corner. 

For more information on trims check out this guide. 

Common Problems With EPDM 

Tearing 

As resilient as EPDM rubber roofing is, it can experience tearing due to excessive wear. You can avoid this however by being as careful as possible. For example, when standing ladders or placing heavy loads onto it, use a plank underneath to spread the weight evenly. Repair kits for EPDM roofs can also be purchased if need be.  

Shrinkage 

Your EPDM roof can suffer from shrinkage for a number of reasons. The first is that the rubber membrane wasn’t given enough time to relax during installation, or due to improper fitting. You may also find that EPDM can shrink over time, pulling away from walls, flashings and other areas. This can lead to serious issues such as leaks, so it’s important to act quickly and consult a professional. 

Bubbles and Blisters 

Bubbles and blisters can form in an EPDM roof for a variety of reasons. While they will not usually cause serious issues, it’s important to watch out for them; particularly if they appear along the seams. Bubbles can form as a result of the vapour released from bonding adhesives used during installation. If these are not allowed to dry fully before applying the roof membrane, bubbles can form. 

Mould or Mildew Build-up 

While mould or mildew growth is not promoted or supported at all by EPDM rubber, it can still happen due to conditions outside. Thankfully, neither of these problems will harm your roof’s structure, but they’re not pretty to look at and can be tough to deal with. If you do spot moss, mould or mildew on your roof, clean it with vinegar using a soft sponge or brush. 

More Information 

If you would like to find out more about EPDM have a look through Roofing Megastore’s great range and if you have any further questions or queries you can call the team on 01295 565565, chat to them online via the instant chat or email them on [email protected].  
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