Case 5
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Cause of Defects
The membrane had not been laid properly, probably done by some unskillful workers and the lack of supervision during construction. There is inadequate stretching of the membrane during application; the hot asphalt applied underneath could be lightly coated, or even bare.
When water vapour from the building interior flows upward through the roof deck, it condenses within the base felt. With cumulative moisture absorption, the felts swell and buckle, forming ridges directly above the insulation joints. This is illustrated in the figures below.