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Community and Q&A

Rockwool Comforboard average waste calculation

Stephen Murdoch | Posted in Green Products and Materials on

Looking for advice from anyone who’s installed exterior rockwool before – could you estimate (or even better did you calculate!?) the amount wasted?

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  1. Expert Member
    Dana Dorsett | | #1

    That would be so project-specifics dependent it will never be clear whether any random answer would be relevant to YOUR project. Calculate it based on your actual project dimensions.

  2. Stephen Murdoch | | #2

    Dana - you don't think that a person could share the percentage they wasted? Isn't that a bit helpful?

    1. Expert Member
      Dana Dorsett | | #4

      A person could share that information, but unless the window & door sizing & spacing, wall heights and widths are the same as yours it's not very helpful.

  3. Andrew C | | #3

    To estimate waste, you need to do some basic area calculations, and then think about layout for standard size pieces of insulation. And if you do two layers of insulation, there needs to be some offset so the seams don’t line up. This is worth thinking about beforehand, and a prerequisite for ordering materials, so it’s probably worthwhile to do this exercise for your specific project, with all its fenestration included. It's not a waste of time.

  4. Zdesign | | #5

    Typical waste factor on all building materials is 10%. I'd recommend determining exactly how much material you need and see how that works out with the quantities that come in the bag. Typically your going to have extra in the last bag and that can serve as your waste factor depending on the size of the project.

  5. Jamie B | | #6

    If you really want to get down to nuts and bolts, you can model it on cad.

    As in take your exterior design drawings, make a 4x8 block on a different layer, lay them out on the exterior, stagger them and adjust for windows and doors, then count how many total boxes you have, or isolate the layer, select them all and the properties panel will count it for you.

    1. Stephen Murdoch | | #7

      Jamie B - Exactly the direction I'm thinking of going. Thanks all for the feedback. I'm sure you'll hear from me again soon.

      1. Expert Member
        Malcolm Taylor | | #8


        You've gotten good advice, I would just add that the waste from insulation is fairly dependant on the installer's approach. If you want to spend the time piecing in scraps, you may end up with next to no waste, whereas if you want to stick with large partial boards, and minimize seams, you will end up with a larger pile when done.

  6. GBA Editor
    Peter Yost | | #9

    I like how our GBA community provided both general practice information as well as how that general estimate of waste is affected by project-specific information.


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