Exterior ceiling and soffit areas are common to many building types and require products that are specially formulated to resist sag caused by exposure to excessive heat and humidity. In commercial construction, examples include covered walkways, open parking garages, bank teller drive-through canopies, marquees, or the underside of any upper floor or roof that extends past the exterior wall. Residential applications include breezeways, covered porches and the soffits formed by the eaves of a house.
Historically, gypsum soffit board was used for exterior soffits. This product was distinguished from interior gypsum board by its moisture-repellent paper and special additives for sag resistance. Traditional moisture-resistant gypsum board, or “green board,” utilized wax in the gypsum core to achieve its moisture resistance and was unsuitable for exterior soffits due to its poor sag resistance.