Plenum Truss-Keepin’ the Ducts Inside - GreenBuildingAdvisor

Building Science Plenum Truss-Keepin’ the Ducts Inside A plenum truss is one method to keep ductwork inside the conditioned space of a home By Randy Williams | March 26, 2026 Illustration Credit: Steve Baczek More Building Science Have You Seen What's Hiding Behind That Drywall ... Buried Ducts in Humid Climates Without Condensation From the Fine Homebuilding Archives—Testing and Sealing Ductwork Can Clean Energy Eliminate All Rejected Energy? The first article I ever wrote for GBA was back in 2020, titled Keeping Ducts Where They Belong. It was all about the issues I see when ducts are installed outside the conditioned space of the home. I even mentioned in the article that of the new homes that fail the code required blower door testing I conduct, most have ductwork outside the building enclosure.So, what’s changed since I wrote that piece? Not very much. A couple months ago I had another failed blower door test because of ducts in the unconditioned and vented attic. As a matter of fact, it failed its second test as well.Why ducts outside the envelope cause problemsWhen ductwork is located in unconditioned and vented attics, vented crawlspaces, attached garages, or any other location that is outside the thermal and air boundaries of the home, there can be a whole host of problems. Holes through the air barrier are needed to extend the duct system into the conditioned space. Insulation may be displaced where the duct moves through the thermal boundary. Air leaks in supply...