What is EPDM? EPDM stands for ethylene-propylene-diene monomer and is a synthetic rubber used as a roofing membrane for flat roofs. EPDM is supplied in one seamless piece, seals completely waterproof and is resistant to UV radiation. That makes it one of the most reliable solutions for the flat roof of a canopy, garden house or veranda. In this guide we explain what EPDM is, how it works and when to choose it.
Houthandel Jan Sok in Meppel supplies EPDM as a complete kit — membrane, adhesive and finishing — for private customers, self-employed professionals and contractors from the same range.
Definition
EPDM is a synthetic rubber roofing membrane. The abbreviation refers to the three monomers that make up the rubber: ethylene, propylene and a diene. This composition produces an elastomeric material that retains its flexibility, even at lower temperatures. Unlike bitumen, EPDM is not bonded in strips, but laid over the roof as one custom-made piece. There are no seams for water to penetrate — which is exactly what gives the material its reputation as a waterproof roofing membrane.
Properties
Three properties determine why EPDM is so suitable for flat roofs of canopies and garden houses:
Seamless — the membrane is made to measure and installed in one piece. No overlaps, no welded seams, no weak spots where moisture can infiltrate.
Waterproof — EPDM seals completely against rain, meltwater and wind-driven moisture. On a flat roof where water does not always drain immediately, that is the most important property.
UV-resistant — the material does not discolour or crumble under the influence of sunlight. That also makes EPDM suitable for roofs that are permanently exposed to the weather.
In addition, EPDM is flexible at cold temperatures, tear-resistant and resistant to ozone. In practice, different figures are given for the exact lifespan; it is generally assumed to have a long lifespan, often 50 years or more, but we do not state any precise guarantee as fact.
Applications
EPDM is most commonly used on flat roofs of wooden outbuildings. Three common situations:
Canopy — a freestanding or attached canopy with a slightly sloping or flat roof.
Garden house — the roof of a garden house or shed where bitumen eventually cracks.
Veranda — a covered seating area where the roof is exposed to weather and wind.
For all these applications the same applies: the substrate must be flat, dry and clean, usually in the form of a roof boarding such as Douglas. Read more about the basis for this in our guide what is Douglas wood and see examples in canopy attached to house.
Pros and cons
Advantages
Seamless and therefore virtually leak-proof. UV-resistant and flexible at low temperatures. Suitable for flat roofs where bitumen falls short. Available as a complete kit with adhesive and finishing.
Disadvantages
Higher purchase price than bitumen. Requires a tight, dry and clean substrate. Installation demands care; a slipped membrane is difficult to correct.
Maintenance and installation
EPDM is low-maintenance. Removing leaves annually, keeping the membrane clean and checking the finishing is usually sufficient. Avoid sharp objects on the roof and do not leave snow lying too long.
Three basic rules apply during installation: the substrate must be dry and dust-free, the adhesive is applied to a grease-free surface, and the membrane is rolled out without pulling. A detailed step-by-step plan can be read in EPDM roof canopy. For the right material we refer to EPDM roofing and accessories.
Frequently asked questions
Is EPDM better than bitumen?
For flat roofs of canopies and garden houses, EPDM is usually the better choice because it is seamless, UV-resistant and flexible. Bitumen is cheaper but has welded seams that can leak over time.
How long does EPDM last?
EPDM has a long lifespan; 50 years or more is commonly mentioned, depending on installation, maintenance and exposure. We do not state an exact guarantee as fact.
Can I install EPDM myself?
With a good kit, dry weather and a tight substrate, self-installation is feasible for a handy do-it-yourselfer. Follow the step-by-step plan and work with two people.
Do I need roof boarding under EPDM?
Yes. EPDM lies on a flat, dry substrate, usually a roof boarding such as Douglas. The membrane follows the substrate, so unevenness remains visible.