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Mystery Holes

qiePo8UT84 | Posted in General Questions on

Hello, I have a question I’m hoping that someone can help me with. I bought a 1982 24′ x 40′ ranch in maine (Zone 6A) that needed to be gutted. While doing the renovations I noticed that at the top plate, bottom plate and through the sill plate on the exterior walls there were 2 – 1″ dia. holes drilled in each bay.

I’m not sure why someone would do this? The house is sided with vinyl siding on top of Masonite siding and the only thing I can guess is its some kind of remediation to fix the problems with the Masonite siding. I have a major problem with ice damning & mice and want to plug these holes up but I’m not sure what effect it will have. I have researched this and cannot find an answer.

Can anyone please help me? Thank You

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  1. bdrfab | | #1

    If I didn't see pieces of the fiberglass I would have guessed they were drilled for installing blown in cellulose. Yes, covering those hole will help with air tightness and have a positive effect in your energy consumption, and probably mice. Do a search for ice dam's on this site and you'll find all sorts of info to help with those

  2. GBA Editor
    Martin Holladay | | #2

    I agree: It's OK to plug the holes.

  3. qiePo8UT84 | | #3

    Thank you for your responses. The house is insulated with all fiberglass and even with the holes is very energy efficient. I have done a lot of reading on how to stop ice dams. My worry is if I plug these holes and they were put there to air out the walls (which I believe is why they put them there) if water was getting behind the masonite siding will that get moldy? The vinyl siding is only on 3 sides and not done well. I know the easy answer is to plug the holes and reside the house but I don't have the money to do that. Does anyone have any experience with masonite siding getting moldy? Also if I plug the holes should I use fire stop or just plain foam insulation? Thanks again.

  4. GBA Editor
    Martin Holladay | | #4

    There is no possible problem with fiberglass-insulated stud cavities that could be solved with this type of ventilation holes. It's not a useful solution to anything; these holes seriously degrade the thermal performance of the wall.

    If water is getting behind your siding, the sheathing should be protected by a WRB such as asphalt felt. However, if you have a water-entry issue, the solution is NOT to drill holes in your bottom plate. The solution is improvements in your wall flashing and your WRB.

  5. qiePo8UT84 | | #5

    I totally agree. I just couldn't fathom why someone would do such a thing. I posted this on the Finehomebuilding breaktime forum and someone replied with this.
    ""With masonite sideing over what looks like plywood sheathing they could have put the holes in the plates to create some ventilation in the stud bays to help dry them dry out. I saw a lot of siding installed directly over sheathing back in the 80's. No house wrap of felt paper used at all.""
    This could explain why the holes are there. I am just not sure I should plug them until Im ready to replace the siding if this was part of the design of the siding. Has anyone else heard of this method of siding? Seems crazy.

  6. bdrfab | | #6

    Sorry, I think I missed something, I thought the holes were in the sheathing. I've never heard of that, but just because it's crazy doesn't mean someone didn't try it. As Martin said, I hope there's some housewrap on already. Use the fireblock Great Stuff.

  7. qiePo8UT84 | | #7

    There is something behind the siding, it looks like tar paper but its tan. Not black like I would think it would be like. Mind you Im not very nolagable about this stuff. At least now I have an idea on what I need to do.
    1.) Insulate for the ice damns.
    2.) Plug the holes and reside the house.
    3.) Put a new roof on.
    Thanks for all your advise.

  8. GBA Editor
    Martin Holladay | | #8

    The tan paper is called rosin paper. It doesn't do much on walls.

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