A Little Known Solar Racking Problem: EPDM and Asphalt

By SunModo 0

When planning to install a rooftop solar system for a business or home, it is important to make sure all the components of the solar mounting products are compatible with the roof. There are a number of issues that can crop up such as the fact that commercial roofs can’t always sustain the weight of solar panels and ballast blocks, plastic components of some systems are not always fire resistant, or roof membrane type can bring certain complications. A particularly important, and little known, issue is that EPDM’s chemical incompatibility with asphalt shingles can result in serious roof damage and premature roof failure.

The Problem with EPDM

EPDM (ethylene propylene diene monomer) is a very popular synthetic rubber across industries due to its low cost, durability and moldability. A good number of roof attachments in the solar racking industry use EPDM gaskets to create a watertight seal around the roof penetration. While these gaskets are traditionally separated from roof shingles with metal flashing, there are a number of new roof attachments entering the market that don’t use this flashing in order to offer cost savings and easier installation. However, this is problematic due to the fact that EPDM is not compatible with bitumen, or petroleum-based, products.

Asphalt shingles are practically solid sheets of petroleum. Due to their low cost, ease of install and availability in dozens of colors, asphalt shingles are the most popular choice for residential roof coverings and many commercial buildings. Unfortunately, contact between asphalt shingles and EPDM causes a chemical reaction that has the EPDM gasket become brittle and eat into the shingles. This is because the rubber component of EPDM degrades when in contact with any bituminous material, something studies on the molecular interaction of rubber with asphalt have confirmed. As a result, EPDM gaskets should never come in contact with asphalt shingles.

A Compatible Solution

Silicone rubber is a very good substitute for EPDM rubber. It has material properties that make it ideal for outdoor applications, and silicone coatings are often applied to roofs to provide a layer of protection that helps extend the life of the roof. Silicone rubber is compatible with concrete, TPO, PVC, EPDM roof coverings and, of course, asphalt shingles. Opting to use solar mounting products that use silicone gaskets over EPDM gaskets is the best choice, particularly when looking to mount a PV system on a roof with asphalt shingles.

In summary, while it is important that designers, engineers and contractors strive to save money when working on rooftop solar projects, they should do so in a way that does not compromise the integrity of the roof. Understanding the incompatibility between EPDM gaskets and asphalt shingle roof coverings can be the difference between significant long-term roof damage and a fully functional roof and profitable system.