Case Studies

Blanket Insulation Services Case Studies: Making the upstairs warmer: Leaky, poorly insulated Cantilever

Wednesday, February 22nd, 2017 by Kevin Bailey


Many homes were built with a cantilevered floor that sticks out past the wall below it. The problem with this is the section that sticks out is completely exposed to the outside. Add to that, builders almost never air seal and insulate these assemblies. So not only do you have a huge void in the floor that allows the warm air you are paying to heat in the winter to leak out. But you have massive heat gain occurring in the summer at this part of the house causing the upstairs to be very hot and humid. The air leaking at the cantilever was causing the floors and rooms above, and the ceiling and rooms below to be uncomfortable. Compounding the problem with keeping the rooms on the second floor, along these cantilevers , comfortable are supply ducts that are routed through the cavities of the cantilevers. And since these areas are not air sealed and exposed to the outside air, the ducts are not effective at fully supplying heat in the winter, or cool air in the summer. This customer wanted to make their master bedroom more comfortable year round. The cantilever was the fix that was needed to achieve that! 


We removed the siding and sheathing allowing us to access the cavities in the cantilever. As you can see in the photo, the cavities were bare. No insulation. Just open floor cavities. We then used spray foam insulation to seal off the cavities, eliminating air leakage that's occurring. A key detail was stuffing around a supply duct in the cantilever and actually spray foaming the duct to ensure its air tight, and well insulated so it can fully supply heating and cooling as it was meant to do. After spray foam has provided our air seal (and about an R-14 with 2 inches of foam) we added an additional R-15 of fiberglass batt as filler for the remaining 5 1/2 inches of cavity space. This resulted in dramatic air leakage reduction, and more comfortable rooms above and below the cantilever between floors. This treatment works great!  

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