The quest for dryness

Moisture in concrete roof decks is a growing problem that needs to be addressed

Roofing contractors have been installing roof systems over new concrete roof decks for decades. In the past, contractors and designers gave little thought to moisture in concrete decks; the only concern was how well a roofing material could adhere to a concrete surface. This was the norm through the 1990s and into this century. However, at the turn of the century, more claims by building owners of roof system failure caused by concrete deck-sourced moisture began to emerge. Photo 1 shows the result of a roof system unknowingly installed over a moisture-laden concrete deck.

Photo 1: This roof system was installed over a lightweight structural concrete deck in the upper Midwest. The roof had only been in place for a matter of months before wind delaminated the moisture-weakened polyisocyanurate facer at the membrane level. Small amounts of condensed moisture are visible on the concrete surface.

The problem quietly simmered for about a decade. Then, the issue was put in front of the roofing industry by several papers published for the 2011 International Roofing Symposium, by the Midwest Roofing Contractors Association and NRCA. The papers focused on extra moisture in the aggregates used in lightweight structural concrete. But these papers and others that followed lacked directions or solutions for how to assess a concrete deck, what moisture levels in concrete are too high and what to do if they are too high.

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