Commercial and flat roofing: TPO and EPDM explained

Why flat roofs need a membrane

A pitched roof sheds water quickly, so shingles can overlap and let gravity do the work. A flat roof is not truly flat, since it has a slight slope toward drains or gutters, but water moves slowly across it and can sit in low spots. That is why low-slope roofs are covered with a single, continuous sheet, joined at the seams so water has no gaps to find.

Flat roofs are common on commercial buildings, apartment buildings, garages, porches and additions. Omega Exteriors installs commercial and flat roofing using TPO and EPDM membranes, for both homes and businesses.

What TPO is

TPO, short for thermoplastic polyolefin, is a single-ply roofing membrane, usually white or light in color. Because the surface is reflective, it absorbs less of the sun's heat, which can help keep a building cooler in summer. Omega Exteriors describes TPO as resistant to UV exposure, punctures and chemicals.

One of TPO's strengths is how its seams are joined. On Omega Exteriors' TPO installations, the roof is inspected, the surface is prepared clean and dry, the membrane is laid and secured with mechanical fasteners or adhesive, and all seams are heat-welded for a watertight finish. A heat-welded seam fuses the two sheets into one.

What EPDM is

EPDM, short for ethylene propylene diene monomer, is a synthetic rubber membrane, usually black. It has been used on flat roofs for decades. As Omega Exteriors explains in The Benefits of EPDM Roofing, EPDM resists UV rays, ozone and extreme weather, and it stays flexible through temperature swings, so it handles cold winters and hot summers without cracking.

EPDM seams are joined with adhesives and seam tapes rather than heat. Installation starts with an assessment of the roof and careful preparation of the surface so the membrane bonds well.

TPO and EPDM side by side

• Color: TPO is usually white and reflects heat; EPDM is usually black and absorbs it.
• Seams: TPO seams are heat-welded; EPDM seams are joined with adhesive and tape.
• Flexibility: EPDM is a rubber membrane known for staying flexible in the cold; TPO is a stiffer plastic sheet.
• Summer heat: a reflective TPO roof can help buildings that run air conditioning; a dark EPDM roof gains more heat from the sun.
• Use: both are installed on commercial buildings and on flat roofs of homes.

How to choose for your building

The right membrane depends on the building more than on the material. A building that is cooled in summer may benefit from a reflective TPO roof. A roof with a lot of rooftop equipment or foot traffic needs a membrane and installation that can handle it. The condition of the existing roof matters too: whether the old roof can be removed cleanly, whether the insulation underneath is dry, and whether water drains properly or sits in low spots.

For a business or an apartment building, timing and disruption matter as much as the material. Omega Exteriors' commercial roofing process begins with an assessment of the project and the existing structure, followed by a plan built with the client, the installation, and a quality check at the end. For HOAs and apartment communities, see multi-family and HOA roofing.

• Is the building cooled in summer?
• How much rooftop equipment and foot traffic does the roof see?
• Does water drain well, or does it pond in low spots?
• What is under the current roof: is the insulation dry?
• How will the work be scheduled around the people using the building?

Caring for a flat roof

Flat roofs last longest when someone looks at them regularly. Keep drains and scuppers clear of leaves and debris, watch for standing water that remains well after rain, and have seams and flashing around equipment and walls checked, especially after a storm. Small problems on a flat roof are much easier to fix before water gets into the insulation below.

To talk through a flat or commercial roof, call (651) 998-8500 or request a free estimate.