Rvalue Please consider this extra thickness requirement when designing blocking heights and specifying fastener lengths ASHRAE Climate Zone IECC 12 RValue Requirements Polyiso Thickness to Meet IECC OLD LTTR Method NEW LTTR Method 1, 2, 3 R 2 Layers 17" 2 Layers 18" 4, 5 R25 2 Layers 21" 2 Layers 22" 6 R30 2 Layers 25" 2 Layers 26"Attic Insulation Houses in a cold climate should have a minimum of R49 in the attic, which is equivalent to approximately 16″ of fiberglass insulation Warmer climates only require an R38 or higher, or about 12″ or more Wall Insulation While wall insulation is limited by the width of the studs, different materials provide higher or lower Rvalues3 050j 065 030 30 13 5 / 8 19 5 / 13 f 0 5 / 13 4 except Marine compressed battR‐value in addition to thefull thickness R‐value b • Exterior foundation insulation shall have a rigid, opaque and weather‐resistant protective
All About Insulation R Values
