Cantilevered Floor – Comfortboard Outsulation? - GreenBuildingAdvisor

Cantilevered Floor – Comfortboard Outsulation? kurthicks | Posted in General Questions on March 25, 2026 10:41pm I’m working to air seal & insulate a small cantilevered floor system in climate zone 4C (western WA). It’s about 6’x8′ and framed with 2x8s, between which is some unfaced fiberglass; 1/2″ ply is nailed on the underside of the joists. Access is reasonable, with about 30″ of clearance from slab to the bottom of the joists. I’m looking at a time-efficient way to improve this assembly and was wondering if anyone has done an outsulation approach to cantilevered floor systems. My thought is to: 1) retain the existing assembly2) seal any seams & penetrations in the plywood soffit and perimeters3) install a self-adhered WRB4) add 2″ Comfortboard on the bottom, leaving it exposed. Is this a reasonable idea?  Thanks for any ideas!Kurt Answer GBA Detail Library A collection of one thousand construction details organized by climate and house part Search and download construction details Join the leading community of building science experts Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field. Start free trial Related Questions Proper Outsulation in Climate zone 2A Shingle Roof Outsulation and Venting Cantilevered floor Outsulation and barrier Replies Expert Member MALCOLM TAYLOR | Mar 25, 2026 11:11pm | #1 Kurt, That sounds like a good plan. I would install an 1 1/2" x 2" wood perimeter to hide ...