Spray foam insulation costs depend on a variety of factors. The first factor to consider is the type of foam. The cost for closed cell spray foam is higher than the cost for open cell spray foam which is 45-65 cents per board foot compared with 70 cents to 2 dollars for closed cell.
The second factor to consider is the amount of time it will take to install the foam. A building under construction where the wall and ceiling cavities are easily accessible takes less time to install than, say, a crawl space where an installer has limited mobility.
Another factor to take into account is how big the total project is. A very small job such as under a stairway, will not take much time or material. For the amount of space covered, however, the cost will be higher per foot than if the installer were spraying the entire inside of a barn.
You should also take into account the quality of the material. Not all foam is formulated the same and there are variations in formulas that contribute to a different cost for one version of open cell foam vs. another version. Your installer will know exactly the right formulation of spray foam that will give you the optimal results for your project and that cost may be higher or lower than the ranges cited above.
The newest innovations in spray foam are formulations which require fewer passes to achieve desired foam depths. Fewer passes means less labor and these new formulas are promising to cut the cost of spray foam even further.
Foam insulation is an investment in comfort and lower utility bills. With a quick payback, the quickest of all insulation materials, foam is actually cheaper in the long run as it never needs replacing and will last as long as a building lasts. Although the upfront cost is higher than alternate and traditional insulation options, spray insulation will lower utility bills more and for far longer.