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SIP panels

cutrightrc | Posted in General Questions on

We are thinking about building are next house with SIPs walls but I have a few reservation. We are located in central NC where it seams is always humid. The house would be ~1800 sqft ranch with a simple rectangular design. Everything I have read about the panels seems great and the ability to get a air tight house with r-27 insulation quickly and easily is very attractive.They offer polyurethane with a few exterior options such as Zip and LP Smartside sheathing, the idea of having the siding already in place seems nice and would speed of the build. My concern has to do with possibility of moisture issues leading to deterioration of OSB and the costly repairs that would involve engineers. Are my concerns valid? Would a panel with siding as the exterior increase the chance of moisture issues. Would a 2×6 design with r-10 exterior be just as quick and cheaper with such a simple house design?

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  1. GBA Editor
    Martin Holladay | | #1

    Q. "My concern has to do with possibility of moisture issues leading to deterioration of OSB and the costly repairs that would involve engineers. Are my concerns valid?"

    A. The type of SIP failure that you are talking about occurs on cold-climate SIP roofs, not walls. I wouldn't worry about SIP walls in North Carolina, but clearly it's always important to pay attention to air sealing details and housewrap (WRB) details. I'm not sure how you can ensure a good WRB if the panels arrive on the site with siding already installed.

    Q. "Would a 2x6 design with R-10 exterior be just as quick and cheaper with such a simple house design?"

    A. It would probably be cheaper, but not "just as quick." SIPs are expensive but they go up fast.

  2. user-626934 | | #2


    SIP failure is definitely not limited to roofs nor just to cold climates. I’ve seen some wall rot here in Virginia at tops of SIP walls due to poor air sealing and stack effect exfiltration. Certainly, roofs are more at risk, though...

  3. GBA Editor
    Martin Holladay | | #3

    Good point. The trouble with fool-proof construction methods like SIPs is that the fools can always figure out a way to screw things up.

    I should remember not to underestimate the ability of fools to do a bad job.

    (Of course, Ryan is no fool. I'm sure that Ryan will do an excellent job of air sealing and water management.)

  4. Expert Member


    I'd go further than Martin. The consequences and rate of of SIPs failures are too high for them to be a good choice of building assembly. Until we have a few years showing SIP construction has dealt with the issues and the failures stop occurring, I wouldn't consider them no matter how skilled the crew.

  5. SwitchgrassFarmer | | #5

    I live in a SIP home; it was quite the undertaking to handle the necessary air sealing to prevent ridge rot.

    I believe those air sealing requirements, and other challenges like the need for a cold roof, rain screen siding system, wiring challenges, required additional structural elements, etc, are often underplayed by the SIP industry.

    My recommendation is that you buy this book, and read it cover to cover:

    Is this the company that you are considering? Found them via Google.

  6. jkstew | | #6

    Malcolm, the first SIPs were built in the 1930s and 40s. The first SIPs with polystyrene foam cores were built in the 1960s are are still performing well today. How much time do you need until they are "proven" for you? Stick frame construction never fails? OSB siding never rots except on SIPs?

    If you are concerned with rot, I suppose you could use MgO2 skins. Those will never rot. Several SIP makers offer MgO2 skins.

  7. Expert Member


    There are some building assemblies that are more problematic than others, regardless of how long they have been in use. Cathedral ceilings are one obvious one, reservoir claddings are another in many climates - and so are SIPs.

    Sure OSB rots and other roofs have problems. What is unique to SIPs are:
    - That the consequences are losing both your finishes and structure.
    - That using the recommended details from many supplier's installation instructions results in an assembly that is very susceptible to failure.
    - That using a product that is manufactured elsewhere often results in the builder holding the bag once things go wrong.

    People are free to use them if they want, but should be aware of the potential consequences.

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