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Retrofit icynene spray in roof rafters

user-1063388 | Posted in Energy Efficiency and Durability on

I have a client with a large uninsulated attic space. Her AHU is located in the attic with insulated duct work. The attic has almost 9 feet of headroom at its peak and the client wants to insulate the 2×6 rafters with icynene (overspraying to give us 8″ of foam). Question. The client is concerned about the fumes from the icynene spraying process getting trapped in the attic and then seeping into the drywall ceiling below in the areas where there is no plywood – near the current soffits and in the area of the ductwork. My installer claims that there is no need as everything will be covered in lastic, but I see her point and feel like forced ventilation immediately after the spraying might be a good idea.


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  1. GBA Editor
    Martin Holladay | | #1

    Best practice recommendations from spray foam manufacturers and reputable installers require the work site to be isolated with polyethylene and mechanically ventilated during and after the foam installation.

    Here's what I wrote on the topic in my blog, Spray Foam Jobs With Lingering Odor Problems:

    "Most manufacturers recommend that a spray-foam work site be isolated with polyethylene barriers and depressurized with an exhaust fan while the foam is being sprayed. This requirement for job-site ventilation is described and illustrated in an online best-practice guide, Health and Safety Product Stewardship Workbook for High-Pressure Application of Spray Polyurethane Foam. The Workbook notes, “Having a negative pressure in a contained work zone will draw in air from small cracks and gaps around the workspace boundary and exhaust the work zone air. Active ventilation is achieved by using one or more fans to draw air to or from the workspace and create a negative pressure inside the workspace. Give careful consideration to the location of the exhaust. Ideally, exhaust is released to an unoccupied space where it is not likely to be drawn through an air intake. This will help protect occupants and workers in adjacent areas from potential chemical exposure.” (The Workbook can be downloaded from"

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