Gypsum firewall assemblies are a smarter alternative for low-rise, mid-rise and tall buildings. Building your knowledge on fire and sound control will achieve better performing, cost-effective and sound assemblies for building occupants in our growing “multiple units” communities.
Officially known as hydrous calcium sulfate, gypsum (or drywall) is composed of oxygen, sulfur, calcium and water. When exposed to fire, the mineral’s water molecules are released as steam, which effectively retards heat transmission through the space for temperatures up to 1038 C as illustrated. When teamed with other high-performance building products, gypsum board can provide optimal fire protection and sound control in firewall and fire separation assemblies. To maximize performance, of these assemblies, it is important to select the right components and place them appropriately.
Firewalls are typically non-load-bearing, two-hour fire-rated (i.e. ULC W311) wall assemblies that run continuously from the foundation to the underside of the roof junction or continue through the roof to form a parapet.
A common design for this assembly, since the changes to the 2010 National Building Code of Canada and subsequent 2012 Ontario Building Codes (OBC), is a wood stud system, consisting of two layers of fire-rated Type X gypsum board installed between a double-row wood-framed wall. This assembly achieves a ULC two-hour fire rating and Sound Transmission Class of STC 61 and is designed with aluminum clips so that one side of the firewall will not collapse the other side.
There are many smarter alternative assemblies for high-performance fire separation assemblies, which utilize gypsum shaftwall panels, Type X and C gypsum boards, and fiberglass insulation. See Free Gypsum Board Systems Manual, CAD & BIM Drawings for more details.
Many components of firewalls and fire separations are helpful in hindering sound transmission between dwelling units. An assembly can increase its STC rating by doubling up on gypsum board layers on each side, installing extra fiberglass insulation in the wall cavity and including an air space, which helps eliminate structure-borne noise. Using double stud walls and a single layer of laminated noise reducing gypsum to dampen sound can also contribute toward a higher STC rating and a thinner wall that provides square foot savings.
There are many different solutions for gypsum firewalls and fire separations with high fire resistance and low sound transmission. For other alternative systems not included in the Manual, working together with the building product manufacturer will result in smarter fire resistant and sound control assemblies being included in specifications and on plans before construction starts which reduces inspection deficiencies and callbacks.