Attic Insulation & Ventilation
Attic insulation and ventilation: insulation depth for a target R by material, assembly R-value from stacked layers, blown-in bags from your bag-label coverage, net-free vent area at 1:150 or 1:300 (2021 IRC R806), and heating-energy savings from added R on your HDD and rate.
Insulation DepthFind how many inches of attic insulation you need to hit a target R-value — R-38, R-49 or R-60 — for cellulose, fiberglass batts, blown fiberglass or foam.Assembly R-ValueAdd up the R-value of stacked attic insulation layers. Enter each layer's thickness and material to get the assembly R-value, with a thermal-bridging note.Blown-In BagsWork out how many bags of blown-in attic insulation you need from your floor area and the coverage printed on your bag label at the target R-value.Attic VentilationSize attic ventilation to the 2021 IRC: net-free vent area from the 1:150 or 1:300 rule, split 50/50 between soffit and ridge, and the number of vents.Insulation SavingsEstimate the heating-season dollars you save by raising attic R-value. Enter area, old and new R, your degree days and fuel price for a conduction estimate.
Every Attic Insulation & Ventilation tool is calculated server-side — visible immediately — with its formula, a worked example and a reference table. Background reading is in the guides.