Estimating Spray Foam Insulation

 Estimating standard insulation is not a very hard process.  You simply find the square footage you are covering and add your materials in to come up with the amount you need and the cost of the products.  Estimating for spray foam insulation is a little more involved because you can have several different scenarios in one space based on how thick you would like the insulation.  Here are the general rules for estimating closed cell spray foam insulation.

Underside of Roof/Attic Closed Cell Spray Foam Insulation Installation

Attic insulation requires a minimum of 5 inches of closed cell spray foam insulation to meet insulation code requirements.  While insulating a flat attic with closed cell spray foam is not a popular practice, insulating sloped ceilings with spray foam insulation is the best way to insulate these particular areas. 

Wall Closed Cell Spray Foam Insulation Installation

Wall insulation requires a minimum of 3 inches of closed cell spray foam in order for the spray foam to meet the permeability and thermal resistance rating required to not only act as an insulator, but as a vapor barrier as well. 

Estimating Closed Cell Spray Foam

If you are estimating the spray foam for a job, you typically are using 600 board foot kits.  600 board foot kits hold exactly 600 board feet.  One aspect of this is that they rarely spray all 600 board feet so it is more accurate to say 550 board feet and use this as your estimating basis. 

Take your square footage of the area you are going to insulate with spray foam and multiply it by how many inches you are going to apply.  For example, I have a house that is roughly 28 x 30 feet with 9 foot ceilings.  To figure out the square footage, you can multiply the total of 28 + 28 + 30 + 30 = 116 and then multiple this by the ceiling height, 116 x 9 = 1044.  This is your square footage.  So 1,044 square feet and you need to apply 3 inches of closed cell spray foam insulation to this area.  To get this figure, multiple 1,044 x 3, since it is a wall, which equals 3,132 board feet. 

Now that you have how many board feet you need to do the job, you will need to figure out how many sets it will take.  Closed cell spray foam is purchased in sets of two tanks which equal one set.  The two tanks contain different compounds that when mixed together in the spray foam gun form the foam in the walls.  To figure out how many sets you need, take your board feet you are going to use for the project (3,132) and divide that by 550 (the amount of usable board feet in a spray foam kit).  So 3,132/550 = 5.69 sets or 6 sets since you can't purchase half or three quarter sets. 

Cost of Closed Cell Spray Foam Sets

Closed cell spray foam sets cost between $500 and $700 per set depending on where you get them.  The best places to get closed cell spray foam sets are from an insulation distributor. 

assuming you can purchase the spray foam for the $500 per set price, 6 sets would cost you $3,000.  Not a small price for insulation, but will perform more consistently with maximum air sealing to fully encapsulate the structure.

Using these formulas will help you figure out if an insulation project is right for you and your home... and your budget.