- Q.In a wood-framed
townhouse with a crawlspace, does the separating firewall start
from the footing and go all the way to the underside of the
roof, or can it start at the main floor and go to the roof,
leaving a continuous open crawlspace under adjoining
units?
A.Bruce Austin,
inspector for the town of Greenfield, Mass., responds: In
townhouse construction, the code-required firewall protects
tenants in one unit from a fire in an abutting unit. Although
the crawlspace runs horizontally, it could still provide a path
for a fire to move from one unit to another, as the fire seeks
oxygen. Thus the firewall must run continuously from the
footing all the way to the underside of the roof sheathing (see
illustration). At the roof, the fire protection, in the form of
type-X drywall, must run 4 feet horizontally in each direction
on the underside of the sheathing. (This is according to the
1999 BOCA code; the ’93 BOCA code requires 2 feet of
horizontal protection at the roof.)
Besides fire transmission, the code regulations for
townhouses also address sound and smoke transmission. The
one-hour-rated wall assembly shown in the illustration will
meet the requirements for all three items.