EPDM is the sheet material most flat roofs in Oxfordshire end up wearing. Here is how it is installed, where it fails and what a proper job should look like on your extension or garage.
EPDM stands for ethylene propylene diene monomer, a synthetic rubber first used on commercial roofs in the 1960s. On a domestic roof it arrives as a single black sheet, usually 1.2mm or 1.5mm thick, cut oversize so the whole roof can be covered without a single field joint.
That one detail is the reason it has taken over from felt on small and medium flat roofs. Most flat roof leaks start at a seam, and a garage or extension roof under about 12 metres wide simply has no seams to start at.
How a rubber roof goes together
The deck is stripped back to sound timber and any soft boards are replaced. New 18mm exterior grade plywood or OSB3 is laid, screwed at close centres, with the falls checked so water runs to the outlet rather than sitting in a hollow.
The membrane is relaxed on the deck for half an hour so it loses its roll memory, then bonded with water based deck adhesive across the field and contact adhesive at the perimeters. Trims are mechanically fixed, upstands are dressed a minimum of 150mm above finished roof level, and corners are formed with preformed rubber pieces rather than folded guesswork.
Real lifespan and what shortens it
Manufacturers quote 50 years for the membrane and independent testing on early installations supports a very long life for the rubber itself. In practice the sheet outlives the details around it, so 25 to 35 years of trouble free service is a realistic expectation for a domestic roof.
What cuts that short is nearly always workmanship or use: adhesive applied in the wet, upstands left too shallow, foot traffic on a roof never designed for it, or a scaffold board dropped on a cold membrane in January. Rubber is tough against ultraviolet light and frost, and weak against sharp edges.
What it costs in Oxfordshire
For a straightforward garage roof of around 15 square metres, a full strip, new deck and EPDM covering typically lands between £1,800 and £2,900. A single storey extension roof of 25 to 30 square metres with a lantern kerb and two upstands is more often £2,900 to £4,800.
The variables that move the price are access and scaffold, whether the existing deck can stay, the number of upstands and outlets, and any lead or tile abutments that need reworking. Our flat roof cost by system guide breaks the same numbers down against felt and fibreglass.
When rubber is the wrong answer
EPDM does not like standing water indefinitely, so a roof with no fall at all wants correcting first with firrings. It is also not the best choice where the roof will be walked on regularly or used as a balcony, because point loads and furniture feet will find any weakness.
Where a hard trafficable surface is needed, or the roof runs into a complicated set of penetrations, fibreglass is usually a better fit. Our GRP fibreglass guide covers where that line falls.
Checking a rubber roof you already have
Twice a year, clear the outlet, look along the perimeter trims for lifted edges, and check the upstands where the rubber turns up a wall. Small punctures can be patched with the same rubber and a proper primer, and a patch done early costs a fraction of a re cover.
If the membrane has gone chalky and hard at the edges, or the adhesive has released so the sheet ripples badly in wind, it has reached the end rather than needing another repair.
Can EPDM be laid straight over an old felt roof?
It can be laid over sound, dry, well fixed felt with an overlay board, but we rarely recommend it. Stripping back means you see the deck condition and the falls, and you are not trusting a new membrane to a covering that has already failed once.
Does a rubber roof need any coating or maintenance product?
No. The membrane needs no paint, dressing or solar reflective coating. All it wants is a clear outlet and nobody walking on it in hobnail boots.
Will a rubber roof be noisy in heavy rain?
No more than any other flat roof. The deck and insulation underneath do most of the sound deadening, and homeowners rarely notice a difference after a change from felt.
Can you walk on an EPDM roof to clean gutters?
Occasional careful access is fine on a properly bonded roof. Regular traffic needs walkway pads bonded in, which we can add at installation if you tell us how the roof will be used.
How quickly can a rubber roof be installed?
Most garage and single storey extension roofs are stripped, redecked and covered in one to two days, weather permitting, because the membrane goes down in one piece.
Thinking about rubber on your flat roof?
We will measure up, check the deck and falls, and give you a written price with the build up spelled out. No charge for the visit.
Evans Roofing & Maintenance Ltd, Witney, Oxfordshire. Call 07960 482233 for a free written quote.