Cathedral Ceilings

Home in Chicago with sprayfoam in cathedral ceilings.

Spray foam insulation is the best choice for cathedral ceiling insulation. It does not allow air movement that causes moisture and mold. The full cavity can be used eliminating the need for both the ridge vent and soffit vents. This ceiling was insulated to nearly R-35 in a 7-3/4″ deep cavity with an “Open Cell” foam.

Picture of Thermal Imaging of Cathedral Ceiling

Fiberglass insulation in a 8″ thick cavity would yield a stated R-25 but the actual installed r-value would be closer to an R-18 (A 28% Loss). Fiberglass looses 11% of it’s R-value when installed “perfectly” in a lab with access to both sides to verify the insulation is square, in contact with all six sides of the cavity, and without compression. In real life that number drops to a 28% loss. Add in air flow and that number drops to nearly a 50% loss by using fiberglass.