In some parts of the country, multifamily builders are replacing masonry parapets with 5/8-inch (15.9mm) Type X gypsum board as a roof underlayment.
|Source: Gypsum Association
In a partial roof underlayment application, the gypsum board is attached to the roof framing and extends on both sides of the separation wall at least the minimum distance required by code (typically 4 feet). Trusses and rafters not covered by the gypsum need to be shimmed to create a straight and uniform base for the attachment of the roof sheathing.
Builders doing multifamily are certainly familiar with building codes requiring fire protection that prevents fires from jumping from one home to the other. In some parts of the country, however, multifamily builders are replacing masonry parapets with 5/8-inch (15.9mm) Type X gypsum board as a roof underlayment.
A parapet acts as an extension of the firewall, keeping a fire from leaping over the wall line into the separate but adjoining living space. Without a parapet, the additional roof protection provided by the gypsum board confines the fire to one side of the wall.
Michael Gardner, a spokesperson for the Gypsum Association, says builders may choose one type of fire protection over another for a number of reasons, including regional and aesthetic preference - a parapet rises 30 to 36 inches above the roof while a roof with the gypsum underlayment is one level plane. The gypsum option doesn’t require a roof penetration and can offer cost efficiencies in large volume production situations because the same gypsum board used for walls often can be used for the underlayment, Gardner says.
The Gypsum Association has developed three International Building Code and International Residential Code compliant methods of installation of gypsum board as an alternative to parapets: full roof underlayment, partial roof underlayment or the ledger strip method. For more information, contact the Gypsum Association at 202-289-5440 or www.gypsum.org.