The short answer: EPDM is one rubber sheet, felt is bonded layers of reinforced bitumen, and liquid cures into a joint-free membrane. What most separates them is how they are joined and how they cope with complicated shapes. Pluvian Roofing installs felt and liquid, and advises on EPDM without installing it.
What are the three actually made of?
Three different ideas about how to keep water out. EPDM is a synthetic rubber supplied as a large sheet, often one piece for a whole small roof. Reinforced bitumen membrane is bitumen toughened with polymer around a carrier, laid in bonded layers. Liquid waterproofing goes on wet, carries reinforcement where the stresses are, and hardens into one continuous layer.
EPDM belongs to the single ply family, alongside PVC and TPO, and how that family compares with bitumen systems as a category is covered in RBM versus single ply. This piece stays with the three materials a householder is usually choosing between.
How is each one joined, and why does that decide so much?
Because joints are where roofs leak, so a material's approach to them shapes everything else about it. EPDM aims to have almost none: on a small roof the sheet arrives in one piece, and where seams are unavoidable they are made with adhesives and tapes specific to the material. Felt has many joints by design, each one welded so the sheets become one thickness of material. Liquid has none at all, because it is applied as one continuous film.
Each approach has a consequence worth knowing. EPDM's few seams are a genuine strength on a simple rectangle and a genuine demand for precision where they do occur. Felt's many welds put the roof in the hands of whoever made them, but a failed lap is a local repair rather than a system problem. Liquid removes the question entirely and replaces it with a different one, which is surface preparation.
How does each one age?
Differently enough that you can usually tell which is which from a photograph of a tired roof. EPDM tends to stay flexible and fails instead at its edges, its terminations and anywhere it has been stressed over an unsupported gap, with punctures the other common story because a single sheet is a single line of defence.
Bitumen systems age from the surface down: the mineral protection wears, the exposed material hardens, and splits appear where the roof has been moving. That progression is slow and visible, which is one reason a felt roof rarely surprises anybody who looks at it. Liquid ages by wear at the surface and by whatever the substrate underneath does, and it is renewed by preparing and recoating rather than by stripping, because fresh material bonds to cured material.
All three last well when they are right for the roof and fitted properly, and all three fail early when they are not. Published life figures come from manufacturers about their own systems rather than about families, so a comparison between two named products means something and a comparison between two words does not.
How does each handle a complicated roof?
This is where the three separate most sharply. A sheet material has to be cut, folded and bonded around every shape it meets, so a roof with several penetrations, an awkward kerb and a change of level asks a great deal of whoever is fitting it, whichever sheet it is.
Liquid has the clear advantage here, because it simply follows the shape and cures around it with no cut edges to close. EPDM is strongest on the opposite roof: a plain rectangle, few penetrations, a clean perimeter, where the single sheet is doing exactly what it was designed to do. Felt sits between the two and brings a practical advantage of its own, which is that it can be combined with liquid at the details, and frequently is.
What does each one genuinely suit?
Different roofs, which is the honest reason all three are still in use. None of them is a compromise version of another.
- EPDM suits small, simple, uncomplicated roofs: garages, porches, extensions with a clean rectangular plan and little on them. Its case is strongest exactly where its seams are fewest.
- Reinforced bitumen suits roofs that will be walked on, roofs that need to tolerate future damage without drama, and overlays onto tired coverings. Layered redundancy and easy local repair are what it brings.
- Liquid suits detail-heavy roofs, anywhere flame is unacceptable, and overlays where a joint-free layer over an existing surface is the neatest answer. Its constraint is the weather while it hardens, covered on our liquid waterproofing page.
Where the choice is only between the two we install, the head-to-head is set out in liquid versus felt, including how a single roof often zones both.
Where do we stand, and what does that mean for the advice?
Plainly: Pluvian Roofing lays reinforced bitumen and torch-on felt, and cold liquid systems. We do not install EPDM. We survey it, we advise on it, and we repair alongside it where a roof already has it.
That matters for how you read anything on this site, so it is worth saying rather than leaving to be worked out. A contractor who fits one material has an interest in that material, and the correct response is not to pretend otherwise but to be checkable: the reasoning above stands on properties anybody can verify, and where a survey concludes that a small simple roof is best served by rubber sheet, that goes in the report and you take it elsewhere.
Which is less noble than it sounds. A roof waterproofed in the wrong material is a complaint waiting to happen, and no roofing firm with any sense wants one on the books. If you would rather have the evidence before the opinion, a condition survey reports what the roof needs regardless of who ends up doing the work.