A Cool Roof Myth

Jerry Beall on Feb 24, 2016 8:00:00 AM

Lately, cool roofs have come under attack by the EPDM Roofing Association (ERA). They are making numerous, albeit erroneous, claims against cool roofs in spite of the science supporting their general benefits. In particular, they are frightening customers with undue concern for accumulative condensation within cool roofs in northern climates.

Cool reflective roofs are not new. In North America, they date to the 1970’s. Seaman Corporation was one of the early pioneers of light colored vinyl single ply roofing. Recognition of the cool roof concept and the science behind it didn’t gain popularity until 1999 with the publication of ASHRAE 90.1 Energy Standard for Buildings.

The success of early cool roof technologies has created an anxiety among the manufacturers of “non-cool” roofs. They have initiated a campaign through the ERA to discredit, or at least cast doubt, on the fundamental science behind cool roofing.

A cool roof is not a substitute for poor roofing design regardless of the climate. Multi-layer insulation, avoiding large gaps between insulation boards, and the proper use of vapor retarders are all sound principles regardless of the roof membrane color.

The presence of high levels of moisture or condensation in cool roofs in northern climates is a scare tactic being deployed by the ERA on fearful building owners. Most roof systems installed without vapor retarders in northern climates may allow small amounts of warm interior air to migrate up into the roof system and condense on the underside of the membrane, regardless of color. This minimal amount of condensation, if it forms at all, will dry out during the summer warming cycle without doing any harm to the roof system components or causing interior building problems.

Proponents of non-cool or black roofs contend that cool roofs allow for greater amounts of condensation, while the summer cycle doesn’t allow the membrane to heat up enough to completely dry out said accumulated condensate.

SPRI, the Single Ply Roofing Industry trade association, sponsored a field study to investigate the condensation phenomena in cool roofs. Ten roofs were selected in ASHRAE climate zone 5. All ten roofs were over 5 years old and consisted of single layer polyisocyanurate insulation installed over steel decks. Test cuts into these roofs were conducted during the winter months.

In seven of the roofs they found no evidence of any moisture; condensation or otherwise. In 3 of the roofs, slight moisture was detected on the backside of the membrane, but no detrimental effects from the moisture were observed.

Seaman Corporation has been installing millions of square feet of FiberTite membrane in “cold” climates since 1979. In fact, some of our oldest surviving roofs are in the north. If condensation was an issue, we surely would have been one of the first to recognize this as a problem.

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