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    New and Retrofit Insulation of Single-Member Cathedral Ceiling, A-Frame, and Flat Residential Roofs

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    By judicious use of sheets of polyisocyanurate foam insulation and properly engineered air spaces, the thermal resistances of single-member cathedral ceiling, A-frame, and flat roofs of existing residences may be substantially increased.

    The paper reviews the typical roof construction and thermal insulation found before retrofitting and the regional aesthetic and practical considerations particular to these roof types.

    A basic insulation system of polyisocyanurate foam sheets with reflective facings is described. The advantages of the facings in enhancing the thermal resistance of the assembly and their inherent vapor retardance is discussed. Variations of the system are shown. The three roof types are divided into five categories and the most appropriate variation for each is selected. Installation details and several cross sections illustrating the important components comprising these insulating systems are presented.

    Two field applications, one exterior, resulting in an increase in thermal resistance from 0.45 K·m2/W (2.5°F·ft2·h/Btu) to 6.44K·m2/W (36.55°F·ft2·h/Btu) and the other interior, resulting in an increase in thermal resistance from 1.26 K·m2/W (7.17°F·ft2·h/Btu) to 4.87 K·m2/W (27.63°F·ft2·h/Btu), are reviewed. Finally, an evaluation is made of preliminary field results, which demonstrates the effectiveness of these new systems.


    polyisocyanurate foam, reflective air space, cathedral ceiling, A-frame construction, flat roof construction, retrofit, vapor retarder, thermal short circuit, thermal resistance

    Author Information:

    de Marne, H
    Consultant, Henri de Marne & Associates, Waitsfield, Vt.

    Committee/Subcommittee: C16.16

    DOI: 10.1520/STP29467S