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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.

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