To figure out how much foam insulation you need, you need to know two things: the area to be insulated (square feet) and the thickness of the insulation (inches). Multiply both and you'll get the number of plank feet of insulation you need to buy. If you choose the “Minimum R value of the code”, our calculator will calculate the minimum amount of insulation that can fit between the struts, joists and beams, to meet the requirements of the building code. The estimate of the cost of insulation is based on the size of the house, the height, the depth of the wall and ceiling structure, the number of openings, the R-value requirements, etc.
You can decide if you only need to meet the minimum amount of Building Code or if you need as much insulation as can fit between the beams. Each product from a chemical manufacturer works a little differently, so the amount of foam required may vary slightly depending on the brand being sprayed. Once you reach a certain threshold, such as the amount needed to create an air seal, you won't get more return on investment by adding additional foam. Closed-cell insulation makes the entire building envelope airtight and eliminates almost 100% of the air leaks that are common with other types of insulation (fiberglass, blowing, mineral wool, etc. The air sealing you want to create in your home can be easily done with spray foam insulation, but only if applied with the right thickness.
The best example is insulating 2 × 4 inch walls (3.5 inches of actual depth of a strut), where the building code requires a value of 15R, cannot be achieved with Open Cell, but is easily overcome with just 2.1 inches of closed-cell foam. Here's an interesting point of view from the “opposite side” on using open-cell foam in attics in warmer climates. This product is designed for enclosed wall cavities, such as framed houses and structures where walls are intact without pre-existing insulation. In short, there isn't much difference in cost (considering the enormous savings in energy costs) when opting for closed-cell foam insulation in attics. In temperate climates, where heat loss is not an important factor, exterior walls with 13R insulation (under construction with 2 × 4 uprights) are quite suitable for keeping your house cool or warm (depending on season).
In temperate and warm climates, there is a battle between builders, architects, engineers and spray foam industry. If you choose not to insulate attic space (that is, only insulate ceiling beams), then you don't need to insulate gable walls. To determine how much spray foam insulation you need for your project, enter your information into our estimation calculator.