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Community and Q&A

Cutting through a thick wall

jay443 | Posted in General Questions on

I am interested in retrofitting my house with either a ducted HRV or something like the Lunos e2. Problem is that I have no idea of how to cut through my walls. I have 2×4 walls but last year I re-sided with 4″ of XPS and a rainscreen system. So in total my walls are about 9.5″ thick. How do I cut a 5-6 inch circular hole in these thick walls?

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  1. Expert Member
    BILL WICHERS | | #1

    You could use a coring bit, but those are expensive. Since a big chunk of your wall is foam, you could try using a hole saw to take out chunks. Run the hole saw until it bottoms out, pull it out, then take the “core” out in chunks using a chisel. It’ll take a while, but you end up with a clean hole. I’ve done this before myself.

    Another option is a sawzall, but you’re pretty much guaranteed to get a messy hole that way. I’m not aware of any jigsaw blades long enough to work here, so jigsaws aren’t really an option.


  2. Expert Member


    Use a small (something around 3/16"), long bit to drill a pilot hole. Then work from both sides using a 4" hole saw.

  3. jay443 | | #3

    These are great ideas, thank you both!

    1. Expert Member
      BILL WICHERS | | #4

      I should have mentioned the long bit and pilot hole Malcolm mentioned. That’s how I keep things lined up when doing my “cut and chunk” hole saw method. I’d commend a long 1/4” but though, since that’s the same size as the pilot bit on most hole saws, and it’s a little more durable and less likely to break while you’re working.


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