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Three types of rubber membranes used on Flat roofs. EPDM, Modified Bitumen, TPO

EPDM – (ethylene propylene diene terpolymer)

  1. The material most Roofing Contractors are familiar with for Flat Roofs, is EPDM. There are obvious reasons why. It’s easier to install. A good sales pitch is “there are “less seems” on the roof because they come in wider rolls.
  2. Seams are a problem with EPDM but not so with Modified Bitumen Membrane or TPO. EPDM seams are glued together with contact cement. This technique has a lot of variables that could influence the outcome of the seems.
  3. Temperature – Can not be too cold or too hot to apply the glue.
  4. Humidity – to much humidity could make the glue not stick to well.
  5. Time – When you apply the glue or Contact cement to both surfaces that should be glued together, you have to wait for it to set, touch dry before you stick the two surfaces together. That waiting time is what starts the problem. Where you started to apply the adhesive and where you ended has a time difference. Therefore the adhesive will set at one end before it sets at the other end.
  6. Not equally smeared – when you brush the contact cement on, it is impossible to be consistent with the amount you apply everywhere.
  7. Preparation – The surfaces should be well cleaned with a chemical – and wiped off. Not very predictable.
  8. Primer – some use primer and some don’t.
There are too many variables and inconsistencies just with the installation of EPDM that it is almost impossible to have a long lasting roof without problems.
After repairing so many EPDM roofs we can say with high accuracy that it’s not the best solution for a Flat Roof.

Modified Bitumen Membranes – There are basically two types

Watch the video on how this Rubber membrane is installed.

The pros and cons of Modified Bitumen Membrane Roofs.

  1. The appearance is not as smooth and clean as EPDM or TPO.
  2. The Torch Down rubber membrane can be installed almost over any surface without much preparation. Unlike EPDM or TPO.
  3. Seams are heat welded and that makes for better adhesion.
  4. Existing flashing that’s already in place eg.where the roof meets siding or skylights, drip-edges, chimneys can be easy reused by just cleaning the old material off. No need to replace it. Unlike EPDM or TPO.
  5. Can almost be installed under any working condition – 30 degrees F to 110 degrees F. Sunny day or moist day. It all is regulated by the amount of heat you apply to bond the surfaces.
  6. If any maintenance becomes necessary due to equipment installation on a roof or any leak is sprung due to unseen problems, this can be done by unskilled people. (using Tar bought at local supply. This happens often) EPDM gets destroyed when Tar is used to fix it. Also happens often.
  7. The Tear factor – Very unlikely to get damaged by traffic or people working. It’s a thicker and tougher rubber membrane than EPDM or TPO.
  8. This is a petroleum based material, therefore can be directly installed over existing tar roofs, other Modified Bitumen Roofs. A double layer of Modified Bitumen Membrane fused together will last almost indefinite. Unlike TPO or EPDM.
  9. The negative part is so many roofers has shied away from this product due to inexperience.

TPO – Vinyl or PVC membrane. (not rubber)

This type of membrane is also heat welded at the seams which make for a secure bond.

1. These systems are more costly to install than EPDM or MB

  1. The TPO membranes reliability has improved in the last 10 years.
  2. TPO roof seams and the transitions to flashing are better than EPDM due to heat welding as to glue down for EPDM.
  3. Much cooler roof than EPDM.
  4. Appearance – very clean and smooth.
  5. Prone to tears due to maintenance traffic.
  6. Shrinks a lot and cause edges to pull up.
Modified bitumen Rubber membrane
TPO vinyl roofing