Closed-Cell vs. Open-Cell Spray Foam Board-Foot & R-Value Calculator
Calculate exact board-footage (bd-ft), R-value achieved, Class II vapor retarder compliance, and turnkey vs. DIY Froth-Pak kit costs for exterior walls, gables, and roof decks across 16x20 to 60x100 structures.
All HoolieHaus architectural CAD plans include exact exterior wall square footage and roof pitch schedules.
How to Use This Tool & Frequently Asked Questions
Tips for customizing dimensions, exporting vector .SVG files, and estimating build costs
How to Use This Tool & Frequently Asked Questions
Tips for customizing dimensions, exporting vector .SVG files, and estimating build costs
Why is closed-cell spray foam preferred over open-cell on metal buildings?
At 2.0 inches thick, closed-cell spray foam forms an impermeable Class II vapor retarder (perm rating < 0.8) and adheres directly to exterior steel panels. This prevents humid indoor air from hitting cold metal sheets, eliminating condensation, dripping, and rust. Open-cell foam is vapor permeable (>10 perms) and can allow moisture to condense against cold steel sheeting.
How do you calculate board-feet for spray foam insulation?
One board-foot equals one square foot of surface area at one inch of thickness (144 cubic inches). Multiply your net wall or roof square footage by the desired foam thickness in inches, then add a 10% to 15% safety buffer for overspray, framing irregularities, and stud cavity geometry.
What thickness of closed-cell foam is needed to meet residential building codes?
Under IECC standards, 2.5 to 3.0 inches of closed-cell foam on 2x4/2x6 stud walls achieves R-17 to R-21, exceeding prescriptive continuous insulation requirements. On roof decks and cathedral ceilings, 3.5 to 4.5 inches achieves R-24 to R-31, which is commonly approved as an engineered unvented hot roof assembly when combined with thermal barrier drywall.
How much does professional turnkey spray foam cost compared to DIY canister kits?
Professional high-pressure heated mobile rig contractors typically charge $1.35 to $1.85 per board-foot installed for 2-lb closed-cell foam. DIY 600-board-foot dual-tank kits cost approximately $800 to $900 ($1.33 to $1.50/bd-ft) for materials alone, making professional installation faster and more cost-effective for whole-house envelopes over 1,500 board feet.