To limit the probability of openings in the joints of flexible sheet material (such as polyethylene) under in-service tensile stresses, which could lead to a loss of airtightness, which could lead to excessive air infiltration and exfiltration through the building envelope, which could lead to excessive heat loss or gain, drafts or high indoor relative humidity, which could lead to the excessive use of energy for heating and cooling, which could lead to an unacceptable effect on the environment.