Rubber in large sheets
The main appeal of EPDM is the size of its sheets. A single piece can cover a wide strip of roof. The roof then has fewer seams and fewer places where water can get in.
The material follows the building's movements between summer and winter without cracking.
Three ways to hold it on the roof
- Fully adhered. The membrane is glued to a cover board.
- Mechanical fastening. Bars or plates screwed to the deck hold it down.
- Ballasted. The membrane is rolled out loose and held in place by a layer of round stone or by pavers.
Ballasted installation is fast and protects the membrane from the sun. The ballast does add significant weight. Before choosing a ballasted system on an existing building, have a structural engineer check the roof's capacity.
Ballast also makes finding a leak harder. The stone has to be moved to see the membrane, and water can travel far under the loose sheet before it shows up inside.
Seams, the system's weak point
Rubber does not weld with heat. The sheets are joined with a primer and an adhesive tape made for this use.
A seam laid on a dirty, damp or poorly primed surface eventually opens. On a leaking EPDM roof, the first places to look are:
- The seams between sheets.
- The upstands along the parapets, where the membrane can shrink and pull on its attachments.
- The flashing around drains, vents and equipment.
Its limits
- Colour. The black membrane absorbs heat. In a borough that requires a white roof or a reflective material when a roof is replaced, it may not be accepted as is. White versions exist. Check the reflectance index on the manufacturer's data sheet and the rule with your borough.
- Oils and grease. Rubber breaks down on contact with petroleum products and cooking grease. Without protection, EPDM is not a good choice near restaurant hoods.
- Improvised repairs. Asphalt-based products are not compatible with rubber. The wrong sealant makes the problem worse.
Which buildings it suits
EPDM suits large, simple roofs with little equipment, where the big sheets give their full advantage, such as warehouses, industrial buildings and institutional buildings.
Depending on the manufacturer and the quality of installation, an EPDM membrane lasts in the range of 20 to 30 years.
Frequently asked questions
My roof is covered in round stone. Is it EPDM?
A roof covered in round stone is not necessarily EPDM. Loose round stone suggests a ballasted membrane, while fine gravel embedded in asphalt points to a tar and gravel roof. We confirm it by clearing a small area.
Can you repair EPDM with tar or roofing asphalt?
No. Asphalt products attack the rubber. The repair is made with an EPDM patch, a primer and a compatible tape.
How long do glued seams last?
How long glued seams last depends on surface preparation during installation and on maintenance afterward. Seams are the first item to check at every inspection.