The Garage Duct and the Panned-Joist Return
A new house has a bonus room over an attached garage. The basement furnace supplies the bonus room through a galvanized duct that passes through the garage ceiling. The return uses a panned floor-joist space that is open to the garage, and the installer sealed the duct penetration with spray foam. The garage/house door has weatherstripping but no self-closer. Two recessed lights puncture the drywall membrane under the bonus room. The contractor says a fire damper is unnecessary “because it is a house, not a commercial building” and wants to close the ceiling.
1. Identify the fire-separation breaches and evaluate whether a fire damper is required at each duct penetration. What exceptions could the contractor legitimately invoke?
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The garage/house separation is a required fire separation, and the duct penetration must not compromise it. As a general rule, an air duct that penetrates a required fire separation needs a fire damper at the separation unless a specific exception applies. The contractor’s “house, not commercial” statement is not an exception.
Possible legitimate exceptions are narrow and fact-specific: the duct may be continuous metal with no openings, the assembly may have a listed alternative, or the code may permit an unprotected penetration in a limited residential condition. The contractor must identify the exact provision and show that the installed duct meets it - material, continuity, clearance, supports and closure. Spray foam alone is not a listed firestop for a duct annulus. The recessed lights are additional breaches, and the panned-joist return is not a duct penetration exception; it is a return-air path that may communicate with the garage.
Require a listed fire damper or an approved engineered alternative, with a listed firestop at the annular space, before concealment.
2. What is the risk of the panned-joist return and spray-foam sealing, and what documentation should be required?
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A panned-joist return uses the joist cavity as a duct. If the cavity is open to the garage, garage air - including vehicle exhaust, fuel vapours and dust - can be drawn into the house. That is a health and fire risk, and it also defeats the required separation. Spray foam may seal air leaks, but it is not automatically a firestop and may not be tested for the assembly. Recessed lights that puncture the membrane create additional openings and may require fire-rated enclosures or protection.
Require the contractor to remove the panned-joist return and install a dedicated return duct with sealed joints. Require listing information for the fire damper, firestop and any fire-rated light enclosures, plus manufacturer’s installation instructions. If an alternative is proposed, require a professional engineer’s design or a listed system evaluated for the assembly. Photograph the open ceiling before concealment.
3. What inspection sequence and corrections would you require before occupancy?
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Inspect before drywall: verify the garage/house separation is continuous, the duct penetration has the required damper and firestop, the panned return has been removed, the recessed lights are protected or relocated, and the door has a self-closer and appropriate fire rating. Check that the duct is supported, sealed and clear of combustibles, and that the spray foam is not being used as a substitute for a listed firestop.
After drywall, inspect the damper access, the door operation, and the return-air path. Require a final inspection that confirms no return air is drawn from the garage and that the separation is intact. If the contractor cannot produce listings, reject the concealed work and require opening of the ceiling. The inspection sequence should follow the construction sequence: separation and dampers first, then closure, then final verification.