DIY Spray Foam Insulation

I have spent the past year debating on how to move forward insulating my attic. I looked at every possible type of insulation in my area and the associated cost. In my Climate zone 5 (Find your Climate Zone) the energy star  recommendation for roof insulation is 49-60 this is impossible with my cape as it stands as I only have 5 1/2 inches of space for the insulation and don’t want to lose space on the interior. I could add insulation on the outside but the cost is too high. This sent me on a journey to find the best possible solution that I can afford.

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I looked into having a company out to spray foam the underside of the roof but the estimate was around $10,000 USD to insulate the house. That was also out of my price range. After hours of searching the web I stumbled upon an article on Green Building Advisor titled “cut-and-cobble-insulation” I was intrigued by this article and nervous about trying to do spray foam myself. It was time to do some real world testing.

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200 board foot foam kit for initial testing

Last October I bought a 200 board feet spray foam kit from my local box store to give the diy spray foam a try. I wanted to get a better cost estimate of the whole project based on the actual yield of the kit. I found that the kit yield was almost exactly what was advertised. 200 square feet at 1 in thickness and was easier than expected to apply. This made the decision for me when buying in bulk you can expect a price of 1 dollar per square foot at 1 inch thickness. So a 100 square foot roof section at 5 1/2 inches deep would cost approximately $550 USD yielding an R35.75 roof (R6.5/inch).

“Closed-cell spray foam provides a higher Rvalue per inch (6.5) than less expensive insulation types like cellulose and fiberglass (3.5 to 3.7). Most spray polyurethane foam is called “two-component” foam. (Green Building Advisor)”

This was still a little out of my Price range so I decided to use a combination of cut and cobble and spray foam. The article called this method “peanut brittle” method.

Here is what I did I bought 20 sheets of 2 inch xps foam R10 and cut and secured this to the underside of my roof decking then added approximately 3 1/2 inches of closed cell spray foam yielding a R32.75 roof. This is a huge improvement from the fiberglass insulation that was there and for a fraction of the cost of using all spray foam. The xps foam  was approximately 44 cents per board foot. So the same 100 square foot section would cost $388 USD. This equates to 30% reduction in cost and only a 10% reduction in the R value. This was the best R value per dollar I could get that fit into my budget and available options.

I’ll be posting more photos and a video of some of the Foam installation later this month.

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Above is a photo of the first coat spray foam over the XPS

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Cut and cobbled 2 in XPS on the roof deck and walls

Below are some related links for additional information

GBA how-build-insulated-cathedral-ceiling

GBA spray-foam-insulation-not-cure-all

GBA there-downside-lumpy-attic-insulation

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