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

Fastener spacing with mineral wool?

user-4405197 | Posted in General Questions on

I’ve read the article I copied below and have done some google searches, but would just like some confirmation if anyone has it. What is the recommended optimum fastener spacing for 1×3 furring strips over 4 inches of Roxul Comfortboard? Framing with 2×6 studs sheathed with Zip Panels. I’m in Oakland County Michigan on a relatively wooded suburban lot. Also, are the double threaded screws like those from Heco Topix (link below) the clear choice for fasteners or could we get away with regular screws? Only reason I ask is that the Heco Topix screws are $2.39 per screw. Thanks for any response.

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. Irishjake | | #1


    Check out Trufast Screws via
    Building Science Corp did the studies/testing for Roxul, you can google it, plenty of info

    Good Luck

  2. Jon_Lawrence | | #2

    Brian - have you checked Roxul's website? They have some very detailed specs there and include the fastener similar to one in the Small Planet link.

  3. GBA Editor
    Martin Holladay | | #3

    Plenty of people have installed furring strips over mineral wool without using Heco Topix screws. Whether the installers consider the task of making sure the furring strips are co-planar to be easy or hard depends mostly on the skill and experience of the installer.

    Reproduced below is the table produced by Building Science Corporation researchers showing that for most types of siding, 1x3 furring strips work fine even if the screws are spaced as far as 16 inches apart. More screws won't hurt, of course, as long as you don't split the 1x3s. (By the way, 1x4s are less likely to split than 1x3s.)

    Here is a link to an article with more information: Installing Mineral Wool Insulation Over Exterior Wall Sheathing.


  4. user-4405197 | | #4

    Thanks everyone and Martin. I saw that article earlier as well. I just wanted to know if 16" was required or even if 24" or 28" would suffice as I saw those spacings as listed for other foams. Also, I spoke with someone that sells the Heco Topix screws, and maybe just because he represents them, he said it was riskier to use regular screws because of expansion and contraction issues leading to condensation on the regular fasteners. He said the smooth break between the threads on the Heco topix allowed for this movement and would keep the enclosure safer. Sounded like he was blowing smoke, as I figured the mineral wool doesn't expand or contract. Is it just convenience then, that someone would go with a double threaded screw?

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |