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Roofing/EPDM directly over tar and gravel



I recently had the flat roof to my garage repaired. I was surprised to find that the EPDM was installed directly over the tar and gravel roof. Doing some online research, I learned that this is not acceptable practice because the tar would weaken the EPDM. I contacted my contractor and he told me as my roof was over 45 years old, "all characteristics and qualities of tar are gone". Is this true?

Thank you for taking the time to consider my question.

Did the contractor remove the gravel before installing the EPDM or was the roof smooth (no gravel on top)? If it was smooth and alligatored like a dry river bed, it is asphalt.

We have a bit of a problem because the common person calls a built-up roof tar and gravel.
The contractor should know the difference if he has any flat roofing knowledge.
Coal tar roofs are young at 45 years of age. I have replaced roofs that are 80-100 years old.
However that being said if it is coal tar it will soften in the heat and still flow under the EPDM and the oils will degrade the rubber.

If it is actually an asphalt based roof membrane and is truly 45 years of age, it is possible the asphalt would be so hard and weathered that it would not flow with the heat build-up under the EPDM. If there is gravel on top it would help divorce the EPDM from the asphalt.

A simple test is to obtain a sample and dissolve it in mineral spirits commonly called Varsol.
If it turns brown it is asphalt, stays solid and a yellow colour occurs, it is coal tar.

Where are you located in Ontario as I am near Toronto?


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D. John Henderson


My 33 years in the building science business has involved air barriers, waterproofing, and flat & steep slope roofing systems.


My roofing encompasses commercial systems (BUR, mod-bit, single-ply) and residential applications (asphalt shingles, cedar shingles, slate and metal. I am cognizant of code stipulations in regards to FM and UL for commercial roofs.

Attended numerous courses offerd by Roof Consultants Institute, Roofing Industry Educational Institute, Factory Mutual Research Corporation, University of Wisconsin, and BURSI. Lectured for RCI and mentored at a local university for a Building Science Certificate.

Past/Present Clients
Government, commercial businesses such as The GAP, hospitals, school boards as a roof designer.

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