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Community and Q&A

Plumbing penetrations in a basement

humm9er | Posted in Energy Efficiency and Durability on

I have a few plumbing holes between basement and 1st floor — all are tight to the wood floor, no big holes under the bathtub or big gaps next to the pipes or anything.

If these plumbing pipes definitely go only to the 1st floor and are under toilets etc, should I still air seal with spray foam? Assume the answer is ‘it can’t hurt’ but I’d be surprised looking at them if they are major sources of air leaks.

My other plumbing holes that run to 2nd floor are already air-sealed with spray foam in the attic. Should I air-seal them in the basement too?

Only reason I ask is access to all these pipes is not fun.

PS. Previous owners had a 12′ x 12′ section of 2″ foil faced poly-iso installed under 1st floor bathroom across the bottom of the floor joists and spray foamed at all seams and at all plumbing penetrations at that area. I assume fiberglass bats run underneath between the joists as that’s how the rest of the basement is. Is this an effective approach? Not typical from what I have seen.

Thank you!

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Justin,
    In general, if both sides of the hole are inside your home's thermal envelope, then there is no need to seal the hole.

    The holes that need to be sealed are holes in your home's thermal envelope.

    Hopefully, you know the boundaries of your home's thermal envelope.

    In the case of plumbing chases or HVAC chases that connect the basement to the attic, however, it's often a good idea to seal both the bottom of the chase and the top of the chase. The reason: these leaks can be hard to seal, and the stack effect can move a tremendous amount of air through these chases. A belt-and-suspenders approach never hurts with this type of vertical chase.

  2. GBA Editor
    Martin Holladay | | #2

    Justin,
    Q. "Previous owners had a 12' x 12' section of 2" foil faced polyiso installed under the 1st floor bathroom across the bottom of the floor joists and spray foamed at all seams and at all plumbing penetrations at that area. I assume fiberglass bats run underneath between the joists as that's how the rest of the basement is. Is this an effective approach?"

    A. You are describing a good approach to insulating a floor assembly. For more information on this topic, see How to Insulate a Cold Floor.

    That said, it isn't usually necessary to insulate the floor assembly above a basement. It usually makes more sense to insulate the basement walls and to bring the basement inside the home's thermal envelope.

  3. humm9er | | #3

    Hi Martin,

    I have long-term plans to insulate my basement walls with 2" foil-faced polyiso

    Okay thank you, I will pull the fiberglass batts away from the plumbing holes between the basement and first floor and run a bead of spray foam around each. I just wasn't sure if there were significant enough leak sources to warrant the effort, but as you said it certainly cant hurt.

    My entire basement ceiling is already insulated with fiberglass bats, with that one area under the bathroom also sealed with the 2" polyiso. In addition, my rim joist is sealed with 2" XPS and spray foam. I will as mentioned add 2" polyiso to the walls sometime in the near future.

    Thanks again for your input.

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