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What is maximum safe thickness of rigid insulation for board and batten siding

lkomenda | Posted in Energy Efficiency and Durability on

I’m building timber framed house with light clay infill between posts. For better insulation I plan adding rigid wood fibre board (steico therm + universal). So far I planned to include 4in rigid outside. Such a wall will give me R 25 and lots of thermal mass inside. I wonder If I can add more wood fibre board safely. What I’m afraid of is sagging of my board& batten siding (on furring strips). Sagging means larger holes in insulation board more air infiltration and thermal bridging. I’ve read some materials on thick rigid insulation in such constriction but test ended on 4in thickness…

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  1. user-2310254 | | #1


    Where are you located?

  2. lkomenda | | #2

    I live in Poland if that metters. It's zone 5.

  3. ethant | | #3

    You're lucky - Steico available right in your backyard! Are you worried about the long term performance of Steico? Perhaps you have more experience with it in Poland? Wood fiberboard insulation is relatively rare here in the US and when I've looked at samples they look too much like cheap MDF furniture for me to trust them for exterior applications.

  4. user-1085194 | | #4

    Back in the 90's I worked for a TimberPeg builder. We used full dimension 1x4 strapping spiked into the timbers over 4" foam board and either 1/2" drywall or 3/4" T&G pine wall finish. You may be able to go thicker with the foam board depending on the spacing of the timbers and strapping. If I remember correctly, TimberPeg used horizontal mid wall beams so there was about a 4' span between nailing surface for the 1x4.

  5. user-2310254 | | #5


    Climate is usually very important. I wanted to clarify that point in case anyone had the experience and knowledge to respond to your question.

    Ethan asked a related questions recently, and it generated a pretty long thread. (See here:

    You will probably have more luck going to a "green" construction site that focuses on the EU. Most of our members are from the US and Canada, and this means the site's content focuses mostly on the methods and materials used in those countries.

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