The roof must be thoroughly cleaned, and allowed to dry thoroughly. This is a critical step to ensure a successful coating application. Be careful not to damage the lap seams. Care should be taken when pressure washing not to disturb the integrity of the underlying roof membrane particularly where there are adhered seams. Refer to the specific coating manufacturer you are using for their specific requirements for roof preparation.

Before filling the wall cavity, spray the perimeter with a 1/2-in. layer, which will expand to a 1-in. layer. These layers are called “lifts.” This will ensure that the foam penetrates any voids where the studs meet the sheathing. This also reduces the risk of bulges in the sheathing. If foam is sprayed into a large gap between the stud and the sheathing and is immediately covered by a thick layer, the pressure of the expanding foam can actually push out any sheathing that isn’t securely fastened. Wait a few minutes after picture-framing the cavity before you go back and lay down the first layer in the center of the wall.
You probably have some familiarity with spray foam insulation, and you may have even used the foam that comes in pressured spray cans at home improvement retailers. This foam is know as one-part foam, meaning that it is one continuous mixture that is simply applied to the area in need. One-part foam is frequently used for sealing small gaps and cracks. http://youtube.com/watch?v=ggLAUsiuI_o
We have a 1950's ranch in Atlanta and are interviewing foam contractors to spray open cell under the roof, with an "ankle wall" out towards the eaves to seal the attic. My wife and daughters are chemically sensitive, so I'm trying to figure out how to minimize the fumes coming into the house. Additionally, at least one contractor has offered (for > $900) to remove our existing rock wool & R-13 fibreglass from the attic floor to "increase cross-ventilation into the attic". Seems to me I can't both minimize fumes AND increase cross-ventilation. They also offered to spray a fire-retardant on for >$600. Would ventilation during installation help any or woud the retardant seal off the foam and help that way? Thanks...

My project was a 2 part one.  First the guest house was to be used for an elderly couple with some health issues.  The idea of using chemicals which can be harmful to the respiratory track has made me change my mind about proceeding. The guest house was single story with a low attic height and 600 square feet and the main house (part 2)  is 2,800 sq feet. After reading the comments below, I would like a quote from someone that uses a soy product that is non toxic. .  
Barrier’s specially-trained technicians have applied over 5 million square feet of coatings in a wide variety of commercial, industrial and residential settings throughout the United States. With our experience, product knowledge and long list of satisfied customers, Barrier is uniquely qualified to give your enterprise the protection it deserves.  
I am an Architect in Toronto. I am designing a new roof addition to a row house building. Because of existing conditions and the shape of the new roof. It may be easiest to use closed cell spray foam within the areas of the joists. My question is when spray foam is used in this situation do I need to worry about how the joist members may be thermal bridges? It is not common to provide a little bit of rigid insulation to protect the joist members? The additional layer of outboard insulation will require an extra layer of plywood above the insulation which will add to cost.

Liquid Roof is a liquefied version of a synthetic rubber typically referred to as EPDM. The letters EPDM stand for ethylene, propylene, diene monomer and M class. Prior to the liquefied version emerging on to the market, rolls of the rubber were used for waterproofing roofs. The liquids are much easier to apply. Can fill cracks and crevices. Liquid EPDM can go where the sheet version could never effectively coat. The liquid roof coatings have more uses. They can be used on RV roofs and other vehicles. They can be applied to a wide range of roofing materials including metal, fiberglass and wood (although wood is not a warrantied application and require the use of the ProFlex primer first). Always consult your roofer to determine if aftermarket coatings are acceptable given the condition of your overall roof. The use of an undercoating means the liquid roof can be applied to built-up and asphalt-based coatings (with the use of the ProFlex primer).
Johns Manville Corbond III® closed-cell spray polyurethane foam insulation offers and R-Value of R-7 per inch and can be applied in a single pass to a maximum of 3.5 inches, providing superior thermal performance with seamless air sealing and moisture control in a single step. Multiple immediate passes, with no wait time, may also be applied. With high yield and excellent adhesion, it's an ideal choice for high-performing energy efficient commercial, residential and industrial applications.
Yes, you're right that all of the problems mentioned above are related to the installer. I didn't try to hide that and even used the word 'installer' in two of the four headings. I can see how you'd think that the title is misleading, but in the end you can't separate spray foam insulation from its installation. Some people have the mistaken impression that if you get spray foam in your house, your home will outperform all others. My point here is that that's not true.
Roof coatings are easy to install. Smaller roofs in good, serviceable condition can be a weekend do-it-yourself (DIY) project. Larger roofs with leaks and ponding water issues should be coated by a qualified professional. Additional roof coating products, such as foam or coatings designed for seams, may be required underneath the main coating layers. Supplement coating products are used to reinforce damaged or leak-prone problem areas.[3] https://m.youtu.be/ggLAUsiuI_o
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