GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

TruExterior Siding and Exterior Insulation / Rainscreen

4khz | Posted in General Questions on

I am an owner builder . The true-exterior manufacturer won’t warranty their siding product when installed on furring strips over rockwool. They state that the furring needs to be fastened directly to a solid substrate.  The primary reason for this is that they get too many calls because of potentially suboptimal installation of the furring. i.e., furring not coplanar, furring strips spacing. Otherwise, they don’t have any issue with the long term performance.

Does anyone have experience installing this product on furring strips over mineral wool ? Is it just too tricky to get the furring coplanar and/or the product just too flexible ? Would you even consider (as owner) since it wouldn’t be warrantied ?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member

    The warranty for most siding / shingles / paint / building materials is rarely worth the paper its written on, IMO.

    It's something of a double edge sword, installing siding on furring, over rockwool. If your walls are nice and straight before installing the insulation, you'll likely have little issue getting the furring co-planar. The blessing of rockwool, compared to {polyiso, EPS, XPS}, is that rockwool will compress, but it can bite you if you don't watch it.

    It's perfectly doable, it just takes {much} more time compared to a typically installation over a flat osb sheathed wall. Get all the furring strips up with as little compression as possible on the rockwool, and then run a few string line at about 4 different heights, leaving them in place, connected at the corners. You can then slowly tighten the screws in the furring strips until you reach a pretty good plane. It's really just a matter of caring about what you're doing, and putting in the time to get it just right before the siding goes up, and then it's a piece of cake.

    Here's a response I gave to someone a while back with a few lessons learned in installing siding over rockwool / furring strips.

    1. 4khz | | #2


      Sorry that I missed your response from a week or so ago and thank you for the info. Are you specifically referring to the Boral siding ? I'm quite confident in getting the rainscreen coplanar when using wood siding, such as pine shiplap. My question is whether it's feasible with Boral - with its additional flexibility. Will the extra flexibility of Boral siding be overly time consuming ?

  2. Expert Member


    I wasn't referring to Boral specifically, but I'm confident that the material has little impact so long as everything is flat. Just make sure it's extra flat! Once you've got a good plane on your furring, the boral doesn't know if it's on a wall or not.

    1. 4khz | | #5

      Ok thanks - I was thinking of possibly using the Boral for siding and in talking with the tech rep, he stated that they get many calls regarding the siding coming out wavy and that's why they don't provide a warranty for furring over roxul.

  3. kyle_r | | #4

    I have used Tru Exterior trim, and I think it’s great for ground contact applications. However it is heavy, floppy (not very stiff), and needs to be handled carefully. I would not want to side a house with this stuff. Just wanted to add that in case you haven’t actually handled the product yet to see what you are working with.

    1. 4khz | | #6

      Kyle r - I handled it a bit in a showroom and that's what I was concerned with (over comfortboard/furring). I was thinking of using it versus pine shiplap w/ tar pine since it's going to be a challenge for me to get the tar pine to dry (need to coat all side before installing). Whereas, I could install the tru exterior right away and paint next year. But back to pine shiplap / pine tar / heat my garage. thanks for confirming.

      I will be using for my water board though. As you mention, it looks like a great application for this !

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |