Spray foam’s thermal performance and advanced air and moisture control can be optimized by combining it with other insulation products like fiberglass batts or rolls, maximizing budget and meeting energy efficiency goals. Combining insulation products creates a custom solution by leveraging the functions of multiple materials to find the best mix for the project. 
In the early days of insulating attics, people believed the insulation was a heat source. That’s not the case, as the insulation is actually a barrier between two areas of different temperatures. As for the “hot roof” theory, the unvented attic system could make the temperature of the roof go up a little, but this increase won’t cause damage to your shingles.
Open-cell is also known as half-pound foam. It has an R-Value of 3.5-3.6 per inch, and its density is bout 0.5 pounds per cubic food. Low-density foams like these are made partially from raw biological materials Carbon dioxide or water is also used in the makeup. Open-cell uses far less material than closed-cell, but its R-Value is lower. Also, open cell requires a vapor retarder (like gypsum wallboard) and is riskier when used for roof sheathing. It's not highly recommended that you use open-cell insulation if you live in a cold climate unless you have that extra barrier. You should also compare how much money you spend versus how effective the open-cell insulation is wherever it's installed.

How Much Is Spray Foam Insulation Installed

Today’s “third generation” of blowing agents have a GWP of 700 to 1000 which is still remarkably high considering water/CO2 has a GWP of 1. However, innovation from some chemical manufacturers like the Chemours Company have introduced the next generation of HFO blowing agents such as Opteon 1100, which significantly reduces the GWP impact when using closed-cell spray foam insulation products.
OK, Peter, I finally went back and read Alex Wilson's article on what he perceives as a serious problem. I haven't seen the full report, but based on the summary he wrote on the Green Building Advisor website, I question the science. It seems to me that he's chosen the wrong metric and he's basing his conclusion on too many assumptions because he doesn't have enough data. You can see my comments at the end of his article.
Also, I'm wondering... Is this website is being regularly updated? A local installer (in Oct, 2010) in MA quoted over twice the price you list here. "Open cell alone ~$1.35 per sq ft for R-13. Or a 'hybrid method' using 2inch closed cell for R-13 followed by 1.5inch open cell for R-6. Hybrid is $2.85 per sq foot for R-19 rating". Maybe installers are charging higher prices to profit from those trying to meet government energy rebate by Dec 31?
I started using Gaco years ago primarily to solve ponding water Problem. It has work well, solved my problems with other roofing options and repairs as well as many other Flat roof issues.  My only problems were experienced when I did not clean the surface well enough for good adhesion.  Follow the Instructions.  Great product and highly recommended. . http://www.youtube.com/v/ggLAUsiuI_o&feature=kp
Part of that guidance will be explaining that interior, two component foam is applied with the professional using specific personal protective equipment (high-pressure foam is installed while using a respirator, for example). It is encouraged that professionals explain clearly to customers that this equipment, coupled with certain work and engineering practices, including ventilation, is used to minimize exposures to the chemicals used to make SPF during the job.

Spray Foam Attic Insulation Cost

As this example illustrates, it's important to seal the envelope completely. One of spray foam's biggest selling points is its air-sealing ability, but it can't seal places where it's not sprayed. One of the nice things about using spray foam in new construction is that you can do a Blower Door test before the drywall goes in. Even better, you can test for leaks with a fog machine. https://youtube.com/v/ggLAUsiuI_o
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The problem was that the installer was doing his first spray foam job ever, and the thickness of the insulation varied from zero (visible roof deck) to about 9". Unfortunately, good average thickness doesn't cut it. The coverage needs to be uniform because a lot of heat will go through the under-insulated areas. (See my article on flat or lumpy insulation performance.) https://youtube.com/watch?feature=youtu.be&v=ggLAUsiuI_o
Sporadic cases of hypersensitivity pneumonitis (HP) have also been reported in workers exposed to isocyanates. The symptoms may seem like the flu, with fever, muscle aches, and headaches. Other symptoms may include a dry cough, chest tightness, and difficult breathing. Individuals with chronic HP often experience progressively more difficult breathing, fatigue, and weight loss. Individuals with acute HP typically develop symptoms 4–6 hours after exposure.[4]
RetroFoam of Michigan has more than 15 years of experience insulating thousands of homes and pole barns across the lower peninsula. We hear a lot of misconceptions about foam insulation and work to make sure we clear up any wrong ideas about foam insulation. Our staff helped us put together this list of misconceptions adding their insights to dispel any misinformation.

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