Concrete roof decks on buildings constructed during the mid-20th
century consist primarily of cast-in-place concrete decks without
stay-in-place metal forms or precast concrete elements covered with
site-placed topping slabs. Both types of construction allow excess
concrete moisture to eventually evaporate from the underside of
roof decks.
Before the proliferation of modern roof systems, a typical roof
system installed onto concrete decks included a continuous layer of
bituminous adhesive that bonded the insulation to the deck. This
water-resistant adhesive, applied at about 30 pounds per 100 square
feet, also performed as an excellent vapor retarder, reducing the
moisture emissions from the concrete into the roofing materials. In
addition, typical insulation products of the past had moisture
storage capacities higher than those of the foam insulations
currently used. Moisture contents of water-sensitive roofing
materials remained below levels that caused them to degrade. As a
result, older roof systems did not succumb to concrete
moisture-related deterioration even though vapor retarder
performance may not have been part of the design.
Although many modern roof membranes and insulations are
moisture-resistant, modern insulation board often is faced with
moisture-sensitive paper facers and is frequently adhered to
substrates with moisture-sensitive adhesives. The change to
moisture-sensitive adhesives is a result of recent volatile organic
compound (VOC) regulations that caused manufacturers to convert to
either 100 percent solids, low-VOC or...
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