Spray Foam Calculator

No. R-value achieved is completely inert to Area to spray and Waste/overspray factor across their full declared ranges -- it only responds to Spray thickness and Foam type, since R-value is simply the material's R-per-inch multiplied by thickness.

It depends on how far you move each one. Near the calculator's defaults, switching Foam type looks like the bigger lever since it's a full option swap. But sweep Spray thickness across its entire 0.5-10 in. declared range and it ends up moving R-value more than any single foam-type swap -- so the honest answer is "it depends how far you're turning each knob," not a fixed ranking.

DIY kits price out on materials alone, but spray foam has a real learning curve -- pass thickness, gun distance, and ambient temperature all affect whether you get the theoretical board feet out of a kit or fall short from an uneven spray pattern. For a job under two or three kits, an experienced DIYer can often come out ahead; for larger jobs, Professional install cost narrows the per-board-foot gap once you factor in equipment rental and the risk of wasted material from an improperly sprayed, over-thick pass that scorches or off-gasses and has to be cut out and redone.

No, they're representative midpoints, not a guarantee for a specific product. Tested R-per-inch varies by manufacturer formulation, and both foam families can lose a little R-value as they age past their initial cure -- open-cell foam can settle slightly over time, and closed-cell blowing agents drift down modestly over the first year or two. Check your chosen product's ICC-ES evaluation report or technical data sheet for its aged R-value before finalizing a plan that depends on hitting a precise code-minimum number.

Not every increase -- DIY kits needed only climbs when Board feet needed crosses another full 200-board-foot increment, since kits are counted by rounding up. But across the full declared range of Area to spray, DIY kits needed only ever increases or holds steady, never drops.