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Spray foam over fiberglass batt

mdhokie | Posted in Energy Efficiency and Durability on

I am building a new house that is required to have a fire sprinkler system. In order to prevent frozen pipes, they are “tented” with a R-38 kraft faced fiberglass batt.

I am in CZ 4, Maryland follows IECC 2015. I am attempting to build a “pretty good” house. My insulation plan for the ceiling is a 1″ layer of closed cell with R-49 blown in fiberglass on top of the closed cell. Attic is vented.

Will the 1″ of closed cell work over the top of the r-38 batts to provide an air barrier? I am having trouble locating good information about air sealing fire sprinklers. Should I have them cover the tops of the batts with 1/4″ fan fold? Or remove the batts and use 1/4″ fan fold as the top of the “tent” which would be sprayed with foam?

Ceiling has no can lights, just junction boxes for surface mount LED lights and pendants. Other penetrations include the sprinkler heads and outlet boxes for smoke alarm.

Thanks for any ideas and suggestions.

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  1. GBA Editor
    Martin Holladay | | #1

    Start by reading this article by Abe Kruger: “Wasting Energy or Catching Fire.”

    Without rereading the article to remind myself of Kruger's advice, I think that your fan-fold idea makes more sense than trying to install spray polyurethane foam on top of fiberglass batts. Whatever you do, make sure that your solution is code-compliant.

  2. mdhokie | | #2


    Thanks for the link and quick response. It seems there is not much knowledge/information about single family sprinkler systems and energy performance. I might live in one of the only states that requires SFD to install sprinklers.

    The attic is mostly truss, and the sprinkler installer did his best to keep the piping as close to the ceiling as possible. Obviously running perpendicular to the truss, it has to be above the bottom chord. Can't drill or notch the truss. We thought about pipes in walls, but the open floor plan needs some sprinklers in the ceiling.

    As the article pointed out, encapsulating the pipe is not recommended in colder climates since the water isn't flowing. The tent basically puts the pipe inside the conditioned space and uses the room heat to prevent freezing.

    I will talk to the insulator about the 1/4" fanfold either over the fiberglass batt or as a replacement. If anyone else out there has experience with insulating and sprinklers, I'd love to hear your strategy.

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