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Community and Q&A

Sealing Plumbing and Electrical Penetrations

sunrisehomestead | Posted in General Questions on

Working on a cool 60’s house. We’re upgrading alot of things but it will never be passive house level. Just a bit more comfortable and durable.

The house is on a hillside with an unconditioned basement/crawl space. There is a stepped CMU foundation wall down the hillside and you can walk under most of the house and crawl under the rest up higher on the hill.

As we demo’d drywall I found alot of prior rat/mice nest areas in the walls as well as alot of dead bugs, etc. I found alot of the plumbing and electrical penetrations through the bottom plate were oversized and the mice/rats were probably getting up into the walls from under the house through these penetrations.

Before we close up the walls I want to detail those so no more rodents can get in but alot of these are pretty sloppy. Big U shaped cuts for plumbing pipes, 1.5″ holes for 1-2 pieces of romex, etc. The plate below the panel has about 20 cords going through it and so many holes that they are almost just one big sloppy messy hole.

I am wondering if anyone has some good ideas for sealing up these penetrations before I close up the walls. Some I could use flashing tape or something but some are so sloppy I don’t know what the best thing would be. I know alot of people would use spray foam but I figured rats/mice might just chew right through it again.

Any ideas for me here?


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  1. Patrick_OSullivan | | #1

    You need a clear delineation of outside vs. inside. Anything sealing outside to inside needs solid materials (wood, metal, etc.). With a protective layer, spray foam can be used to fill large voids to assist in air sealing.

    Tape, foam, goop, none of that can be the protective layer for things with teeth.

  2. Expert Member
    Akos | | #2

    Steel wool is your friend. Fill the big gap with spray foam and push the steel wool into it. Larger gaps you can cover with hardware cloth.

    Critter barrier is best done outside the house, even if the basement is vented, I would critter proof outside not the floor.

    1. sunrisehomestead | | #3

      No wonder I have found steel wool stuffed in holes around many houses. I didn't realize it was a rodent repellant...thought maybe people just stuffed whatever they could find in holes.

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