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It is better to spray closed cell insulation on back of roof decking or over the ceiling joists?

CMRICHA | Posted in Energy Efficiency and Durability on

New construction with cathedral roof.

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  1. user-2310254 | | #1

    Cynthia. Where you are located? Local conditions are important when considering options for insulating a cathedral ceiling. (See this article for additional information: https://www.greenbuildingadvisor.com/blogs/dept/musings/how-build-insulated-cathedral-ceiling).

    [edit] Okay. I see you posted two questions about your roof, but I am having a hard time visualizing it. Can you post a couple of pictures or drawings?

  2. GBA Editor
    Martin Holladay | | #2

    Cynthia,
    I can't tell whether your two recent postings are two ways to phrase the same question, or separate questions.

    If you are insulating a cathedral ceiling with spray foam, then either (a) the spray foam is installed directly on the underside of the roof sheathing, or (b) the spray foam is installed on the interior side of ventilation baffles that are installed under the roof sheathing. (The purpose of the ventilation baffles, which are optional, is to create an air space between the top of the insulation and the roof sheathing. In most cases, this air space is connected to soffit vents at the bottom and a ridge vent at the top.)

    For more information on these issues, see How to Build an Insulated Cathedral Ceiling.

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