New porch floor insulation NH - GreenBuildingAdvisor

New porch floor insulation NH NoCodave | Posted in General Questions on February 14, 2026 12:16pm Hello Hoping to reduce labor and simplify floor insulation. Considering: Wood floor over rubberized underlayment on subfloor sheathing,2 inches high density rigid foam on top of 2×10 joists filled with 9.5rockwool. Bottom layer to enclose.Addition on piers 4ft off ground, open.1) Pt or cdx to bottom of joists.2) Rigid foam 1&1/2 or 2 inches to bottom of joists thenpt or cdx?3) something other than rigid foam under joists, before the pt or cdx? Perhaps some advanced vapor/air barrier?Small porch, nothing heavy, few chairs and small table.Really attempting to reduce all the labor with rigid foam betweenthe joists, then sealing all around each piece with expanding foam.We will be insulating the rim joists.Appreciate the comments and suggestions. 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 Covered porch floor options Insulate porch floor/under gas fireplace Converting porch to living space — insulation plan How to insulate a screened porch floor Replies Expert Member MALCOLM TAYLOR | Feb 14, 2026 12:38pm | #1 Dave, You don't need rigid foam both above and...