+44 7853 968135
EPDM vs bitumen which is better for a flat roof?
For most domestic flat roofs, EPDM is the better material. It lasts longer, requires less maintenance, and is safer to install. That said, it is not the right answer in every situation, and understanding why helps you make a decision that suits your property rather than just following a trend.
What Each Material Actually Is
EPDM stands for Ethylene Propylene Diene Monomer. It is a synthetic rubber membrane that has been used in commercial and domestic roofing since the 1960s. It comes in large sheets, goes on cold using contact adhesive and tape, and does not require any open flame during installation.
Bitumen felt, sometimes called torch-on felt or modified bitumen, is the older, more traditional option. It is a multi-layered system where each layer is heated and fused to the one below using a propane torch. It has been the default flat roofing material in the UK for decades, which is why you still see it on so many garage roofs and rear extensions.
Need some Support with Flat Roofing? Speak with a member of our Professional Flat Roofing Team here
How They Compare
The biggest difference between the two is lifespan. A properly installed EPDM roof will typically last 30 to 50 years. Felt, even the better torch-on varieties, tends to come in at 15 to 20 years before it starts to fail, and that assumes it has been maintained and has not been holding standing water.
What we tend to see with older felt roofs is material that has been slowly saturating for years. By the time a leak appears inside the property, the roof deck underneath has often already taken damage. Felt degrades from UV exposure and temperature cycling. It becomes brittle, the surface granules break down, and the layers eventually separate. In a climate like ours in Surrey and South West London, where we get a reasonable amount of rain and some sharp frosts, that degradation process is fairly predictable.
EPDM handles temperature movement much better. It stays flexible in cold weather and does not crack or blister the way felt can during hot summers. It is also inherently resistant to UV without needing any additional coating.
Installation is another area where the two materials differ significantly. Felt requires a torch, which means fire risk, more preparation time, and a professional installation every time. EPDM goes on cold. The membrane is bonded using contact adhesive, with seams sealed using lap tape. It is a cleaner, faster process, and because there is no naked flame involved, it is considerably safer on a roof above a habitable space.
On cost, bitumen felt tends to be cheaper upfront. That is worth acknowledging honestly. If budget is the primary concern and you are replacing a small garage roof that you do not mind revisiting in fifteen years, felt is not a bad choice. But for an extension on a Surrey semi or a flat roof over a kitchen where you want it done once and forgotten about, the long-term case for EPDM is strong.
The one area where felt holds an advantage is puncture resistance. Thicker modified bitumen systems are more resistant to foot traffic than EPDM, which is why they are still often specified on commercial roofs where trades are regularly walking and working on the surface.
Side-by-Side Comparison
| EPDM | Bitumen Felt | |
|---|---|---|
| Typical lifespan | 30 to 50 years | 15 to 20 years |
| Installation method | Cold adhesive, no flame | Torch-on, open flame |
| UV resistance | High | Degrades over time |
| Flexibility in cold weather | Excellent | Can become brittle |
| Foot traffic resistance | Moderate | High (torch-on) |
| Upfront cost | Higher | Lower |
| Seam vulnerability | Yes, if poorly installed | Less of a concern |
| Best suited to | Domestic extensions, garages | Commercial, high-traffic roofs |
Final Thoughts
For the kind of work we do across Surrey and South West London, flat roof extensions, garage roofs, Victorian terrace rear additions, EPDM is the material we recommend in the vast majority of cases. The upfront cost is higher, but you are getting a roof that will outlast two or three felt replacements and will not need recoating or patching in the meantime.
Felt still has a place. If someone is on a tight budget, needs a quick repair to an existing felt system, or has a commercial property with regular roof access, it is a legitimate option. But for a homeowner who wants a long-term solution and does not want to be back in touch with a roofer in fifteen years, EPDM is the sensible choice.
To summarise the key points:
Need Help with Flat Roofing Matters? Talk to one of our Flat Roofing Experts today!
Frequently Asked Questions
Is EPDM better than felt for a flat roof?
For most domestic roofs, yes. EPDM lasts significantly longer, handles UV and temperature changes better, and requires less maintenance over time.
How long does an EPDM roof last compared to felt?
A well-installed EPDM roof typically lasts 30 to 50 years. Torch-on felt usually lasts 15 to 20 years before it starts to deteriorate.
Is EPDM more expensive than bitumen felt?
The upfront material and installation cost of EPDM is generally higher, but the longer lifespan means it tends to be more cost-effective over time.
Can EPDM be installed without a professional?
It does not require specialist tools or a gas torch, so it is more accessible than felt. That said, professional installation is still recommended, as poorly bonded seams are the most common cause of EPDM failures.
Does bitumen felt need to be torched on?
Most modern felt systems use torch-on application, where each layer is heated with a propane torch. Some older systems use cold-applied felt, but torch-on is the more durable option.
What is the main weakness of EPDM roofing?
The seams and edges are the most vulnerable areas. If the adhesive is not applied properly or the lap tape lifts, water can get underneath. This is why installation quality matters.
Is bitumen felt still used on domestic roofs?
Yes, particularly on garages and outbuildings where budget is the primary concern. It is less common now on extensions and habitable spaces, where longer-lasting materials are preferred.
Can EPDM be laid over an existing felt roof?
In some cases, yes, provided the existing deck is sound and dry. More often, the old felt and any damaged decking is stripped back before the new membrane goes on.
How do I know if my felt roof needs replacing?
Common signs include visible cracking or blistering, standing water that does not drain, felt that feels spongy underfoot, or any evidence of moisture in the ceiling below.
Does EPDM cope well with the UK climate?
Yes. EPDM performs well in cold and wet conditions, which makes it well suited to the UK. It stays flexible in frost and does not degrade under the UV exposure we get in summer.
What is torch-on felt roofing?
Torch-on felt is a modified bitumen system where each layer is applied by heating it with a gas torch, which melts the underside and bonds it to the layer below. It is the most durable form of felt roofing.
Is EPDM a good choice for a garage roof?
Yes. It is one of the most common applications. It handles temperature fluctuations in an unheated space well and, once installed, requires very little maintenance.
Can I walk on an EPDM roof?
For occasional access, yes. EPDM is not designed for regular foot traffic, so if the roof will be accessed frequently, a torch-on felt system or protective walkway boards are a better option.
How much does it cost to replace a flat roof with EPDM in Surrey?
Costs vary depending on size and access, but as a rough guide, EPDM installation for a domestic extension in Surrey typically ranges from £70 to £100 per square metre including materials and labour. Always get at least two quotes and check that the contractor is experienced with rubber membrane systems specifically.