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Stabilized polyurethane sheathing boards

Martin Livingston | Posted in Energy Efficiency and Durability on

We are a Nova Scotia production home builder and are considering taking our projects to the next level towards EQ or NetZero homes. To acheive these levels we need to look at different products. I poked around on the internet for information about polyurethane foams and found statements like this –

Over time, the R-value of the foam drops as some of the gas escapes and air replaces it. This phenomenon is known as thermal drift. When manufactured, the initial R-value is roughly R-9 per inch. Experimental data on this type of foam indicates that most thermal drift occurs within the first two years after manufacture and slowly decreases until it stabilizes at about R-7 per inch. It then remains unchanged unless the foam is damaged.

Foil and plastic facings on these foam panels help to slow the escape of gas from the cell structure. Testing suggests that the stabilized R-value of rigid foam with metal foil facings remains unchanged after 10 years. The reflective foil, if installed correctly, can also act as a radiant barrier (another type of insulation) that adds about R-2 to the insulating assembly. Panels with foil facings have stabilized R-values of 7.1 to 8.7 per inch.

There have been several successfull projects in Canada where the the 2×6 walls have been sheathed with two layers of foil backed foam and cellulose between the studs. I would like to adapt these high performance foams in the same type of assembly. Can somebody recommend a stabilized foam product available in the Canadian market?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Martin Livingston,
    There are three main types of rigid foam insulation: expanded polystyrene (EPS), extruded polystyrene (XPS), and polyisocyanurate. The "thermal drift" problem you write about occurs in polyisocyanurate and XPS, but not in EPS. For more information on this issue, see Thermal Drift of Polyiso and XPS.

    Major manufacturers of polyisocyanurate include Dow Building Materials (the manufacturer of Tuff-R), Johns Manville (AP Foil-Faced), and RMax. I expect that these products are available in Canada.

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