By Brad Oberg
As emphasized in an earlier article in this series (Floor over Garage), safety is critical in a bonus room over a garage, and ensuring safe air quality by airsealing is essential. Cars going in and out of the garage emit poisonous carbon monoxide in their exhaust. Mowers and other equipment along with gasoline, which are typically stored in garages, can also have harmful vapors that could find their way into the living space directly above them. All penetrations—in the floor, knee walls, or ceiling—into the bonus room should be carefully sealed with caulk or closed cell foam, as all of these spaces are connected to the garage.
In addition to proper air-sealing, pressure balancing between the bonus room and the rest of the house is important to indoor air quality. If the supply and return ductwork to the bonus room are not sized according to Residential Duct Systems Manual D, pressure differences can occur. Balancing dampers should be adjusted when the house is finished and the entire system can be balanced for performance. (Remember, when balancing the air-supply system, it is good practice to pressurize the bonus room versus the garage to help reduce infiltration.)
Finally, a means of venting the poisonous gasses from the garage area should be installed where possible. Possibilities for this task include timer-controlled power venting tied to the garage door opener, or a storage cabinet direct vented to the outside of the home to store gasoline and other harmful materials.
Correctly designing and constructing bonus rooms will help to ensure a safe, comfortable space for homeowners. It’s critical for site supervisors to understand that insulation, airsealing, equipment sizing, and indoor air quality are all components that need to be considered to ensure that work is being done correctly. Taking care to properly select and install materials will ensure good performance throughout the home in the long term, thus boosting a builder’s reputation and preventing callbacks down the road.
Brad Oberg is co-founder and chief technology officer of IBACOS, a building-science company based in Pittsburgh. He has directed extensive research into the integration of ventilation strategies, residential ductwork design and performance, improved residential airtightness approaches, and durable construction approaches.
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