A set is two 55-gallon drums: an A-side drum of ISO and a B-side drum of resin, sprayed through the rig at a 1 to 1 ratio by volume. Every yield number on a data sheet is for one full set. Everything below works from that.
Board feet: the one number that matters
A board foot is one square foot of foam one inch thick. Square feet of surface times inches of depth gives board feet.
| Surface | Thickness | Board feet |
|---|---|---|
| 2,000 sq ft of wall | 2 in closed cell | 4,000 |
| 2,000 sq ft of wall | 3 in closed cell | 6,000 |
| 1,500 sq ft of roof deck | 5.5 in open cell | 8,250 |
| 1,200 sq ft of crawlspace wall and band | 2 in closed cell | 2,400 |
| 3,000 sq ft of metal building wall | 1 in closed cell | 3,000 |
Measure the surface you will actually spray, not the floor plan. A 2,000 square foot house can have 1,600 square feet of wall or 2,800, depending on ceiling height and how many gables are in it.
Yield per set
Theoretical yield is on the set's yield card and technical data sheet. It assumes drums and substrate at about 75°F and a rig that is on ratio. The two foams USAFoam sells most are at opposite ends of the range.
| Set | Density | Theoretical yield | At 1 in | At 2 in | At 3.5 in |
|---|---|---|---|---|---|
| Thermoseal HFO, closed cell | 2.0 lb | about 5,000 bd ft | 5,000 sq ft | 2,500 sq ft | 1,430 sq ft |
| Thermoseal 500, open cell | 0.5 lb | about 18,000 bd ft | 18,000 sq ft | 9,000 sq ft | 5,140 sq ft |
Nobody gets theoretical yield on a job. A good crew with warm drums, a warm substrate and a tuned gun gets 85 to 90 percent of it. The rest goes to overspray, trimming, the hose and gun, a cold wall in the morning and the last gallon in the drum. A crew that is consistently under 85 percent has a problem worth finding: cold material, a rig off ratio, a worn chamber or a leak.
The math, with the margin built in
- Board feet = square feet × inches.
- Sets by the math = board feet ÷ theoretical yield.
- Multiply by 1.15 for the loss you will have on a normal day.
- Round up to whole sets, and bring one more than the number you need if running out means a second trip.
| Job | Board feet | Sets by the math | With 15 percent loss | Bring |
|---|---|---|---|---|
| 2,000 sq ft walls at 2 in closed cell | 4,000 | 0.80 | 0.92 | 1, with a second set on the truck |
| 2,000 sq ft walls at 3 in closed cell | 6,000 | 1.20 | 1.38 | 2 |
| 1,500 sq ft roof deck at 5.5 in open cell | 8,250 | 0.46 | 0.53 | 1 |
| 1,200 sq ft crawlspace at 2 in closed cell | 2,400 | 0.48 | 0.55 | 1 |
| 3,000 sq ft metal building at 1 in closed cell | 3,000 | 0.60 | 0.69 | 1 |
The half set left over is not waste. Capped and stored right it sprays next week; see the drum storage guide for the limits.
Working back from an R-value
When the spec gives an R-value instead of a thickness, convert it with the data sheet. Thermoseal HFO is R-7.4 per inch and R-25 at 3.5 inches. Thermoseal 500 is R-4.1 per inch. So an R-21 wall is about 3 inches of closed cell or 5.5 inches of open cell, and the board feet follow from there.
What this means for ordering
Weekly crews buy by the pallet or the truckload and keep a set in reserve; a crew doing a job a month buys by the set and picks it up the day before. Either way the set is priced at your account's rate, which you ask for once at usafoam.co/quote, and the branch page shows what is on the shelf today.