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Community and Q&A

Avoiding Problems with SIP Roof

user-6425079 | Posted in General Questions on

Hi Everyone.

I was listening to Mr. Holladay on the FHB podcast and started getting nervous about my SIP roof built 3 years ago.. We live in central Washington and the climate is pretty cold in the winter (mid 20’s) and hot in the summer (upper 90’s). The humidity levels are low year round. We get about 2-3 of snow on the ground by February. The roof is 1/2:12 pitch and is 64’x32′. The bottom seams of the panels were taped, although the tape didn’t seem to stick all that well. The humidity in the house is around 28-32% year round. The ceiling is painted drywall.

We did not do an air gap on the upper side of the roof. The roofing is metal, which is pushing it for the 1/2 pitch. I icegaurded the whole roof, but those seams did not bond well either. I should’ve used a better product.

My question: should i be concerned about anything?

Also, for the first time, we had an ice dam build up 2 days ago. There was water coming down out of the first seam in the SIPs. Fortunately, it is a large overhang, so it wasn’t on the interior of the house.

Now, I’m wondering should I pull all the roofing off once it warms up and let the thing dry out and also to see if there is any mold. Then maybe replace with a better underlayment and a TPO roof?

Lastly, we just sold the house last month and are renting it back from the new owners through May. So, it’s kind of a tricky situation.


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  1. GBA Editor
    Martin Holladay | | #1

    It's not a good sign that your roof has ice dams -- especially if the house is only three years old. It's especially bad if you have seen water on the underside of your roof assembly.

    I'm not going to give advice on the moral or ethical issue of what you should tell the new owners of the building. I'll leave that issue to your conscience or your lawyer.

    Is the lower photo a photo of your low-slope roof? If it is, it seems to show stripes in the snow, indicating air leakage at the SIP seams. That's not good.

    From the clues in this photo and your description, it appears that:

    1. The installers chose an interior tape with adhesion problems.

    2. There is evidence of air leakage at the SIP seams.

    3. The air leakage at the SIP seams is melting snow on the roof and leading to ice dams.

    4. The slope of the roof is too low.

    5. The "ice guard" product (I assume some type of peel-and-stick) wasn't installed in a way that is waterproof.

    Lots of problems. It would take a site visit to determine whether there is any way to seal the air leakage at the SIP seams from the interior. That would be Step One.

    -- Martin Holladay

  2. Expert Member

    It must be apparent to regular readers here that SIPs assemblies represent more than their fair share of the problems needing remediation - and that they are generally serious problems.

    In the face of that I still see posters proposing to use them on their new builds. There seems to be a real disconnect. What are the features that draw people to use SIPs over equally efficient but much more resilient methods of building? I'm genuinely stumped.

  3. user-6184358 | | #3

    How thick are the SIP roof panels?

  4. SwitchgrassFarmer | | #4

    Malcolm, I live in a SIP home.

    SIPs promise unexcelled performance from air sealing, lack of thermal bridging, and installation speed perspectives. In our case the latter two points didn't work out to be true, because we spent an inordinate amount of time augmenting and protecting the SIPs, from cold roof and rainscreen siding details to additional LVLs/lumber at certain key points.

    When I first saw the original poster's question I cringed. My initial thought was "everybody knows you have to do a cold roof atop SIPs". (Reminds me of the Geico commercials: However that is not the case. For example, there don't appear to be any cold roof images on the SIPA construction details page:

    Lastly, people don't get on Green Building Advisor and post that their SIP roof didn't have condensation and rot problems. They find GBA when they do have problems. What we see here may not be indicative as to the actual percentage of failures versus installed base.

    BTW, I racked my brain trying to come up with a clever analogy for SIPs. The best I could is that they are like a fine British sports car with a Lucas ignition system. Extremely sexy and high performance, but won't start in the rain or fog.

  5. Anon3 | | #5

    If you sold it then it's not your problem anymore, just move.

  6. user-6425079 | | #6

    1. Thank you for the response Martin.

    I think what I'll do for now is go through the interior ceiling and make sure I've air sealed as good as possible, ie. caulk all joints at beams (SIPS rest on glulams), air seal light fixtures, etc. As for the exterior, I'll apply some heat tape to address the ice dam. I'll probably talk to the owner about keeping an eye on things and potentially splitting the cost of doing a cold roof in the next summer or two. Which means, I assume, it'd have to be a metal roof again. This time with a taller standing seam and better tape for those seams. I can't visualize how to vent a cold roof with TPO...

    Should the low humidity levels give me any peace of mind as far as rot goes? If not, how long does it take for stuff to rot?

    2. As for my decision to use SIPS - I like the idea of a R-55 roof installed very quickly. We set (5) 63' beams and a 32'x64' roof in two days. Which may or may not be fast, but it seemed pretty good. Sure, in hind sight, SIPS may not have been the best choice, but it seemed good at the time and I didn't see/do enough research to convince me otherwise.

    3. The SIPS are 12.25" (11.25" of foam).

    4. True.

    5. Also true, but we are renting the place back from the new owner for a few months and more importantly, I want to pass on a well functioning house.

    Thanks everyone.

  7. Expert Member

    GBA is certainly not the right forum to get legal advice on your situation. I would caution about making any assumptions about your liability for the roof problems based on comments here, or your present relationship with the new owner. You need to speak to a lawyer. Quickly.

  8. Expert Member

    There are a number of extreme sports, like rock climbing, that are very safe when performed by experienced, well-trained participants. That doesn't negate the reality that they are inherently more risky that other activities. To me SIPs are like that. Installed by experienced, diligent, conscientious workers they perform as expected (your house is a perfect example). But the chances of success are so much lower than assemblies that are inherently more robust.

    The frequency of questions posted on GBA are no statistical indication of how often these problems occur in the wider building world, but it is clear that there are assemblies, like say cathedral roofs that cause more concern than others. I can't imagine a case being made that SIPs weren't a risky way to build compared to most others.

  9. user-6425079 | | #9

    8. I'm definitely not looking for legal advice on GBA. I'm simply trying to get an idea of the severity, timeline and (possible) solution to the problem. I AM assuming liability based on the fact that I built the house (as a homeowner, not GC) and that I want it to be fixed because its the right thing to do.

  10. Anon3 | | #10

    You should remove your post and your name. And yes consult a lawyer. Anything you do to "repair" it could be used against you.

  11. jackofalltrades777 | | #11

    Best way to do a SIP roof properly:

    1 - Tape all exterior panel seams with a good tape that is vapor permeable to allow for any trapped moisture to escape like SIGA WigLuv tape.

    2 - Install a vapor permeable roof membrane like SIGA Majcoat which has a vapor perm rating of 34.0 PERMS which allows for a decent amount of drying if it gets wet.

    3 - Install an air space between your membrane and finished roof. Even 1" of space will allow for drying. Doesn't take much but just enough to allow for drying.Don't attach a metal or shingle roof directly to SIPS as that prevents any drying.

    4 Seal and tape all interior panel joints with spray foam and a good tape like SIGA Rissan.

    If the above is done, a SIP roof can be as long lasting as a truss roof design with an attic. SIPS have their place but just need the extra TLC and steps to keep them properly sealed and dry. If SIP roofs are done incorrectly, then yes, they can be a problem. Like anything in building science, there is usually a solution, just apply it properly.

  12. GBA Editor
    Martin Holladay | | #12

    Peter L,
    The details you describe are good ones. Siga tapes are not the only brand that would work -- but they are quality products.

    I would also add that a roof with a slope of 1/2" in 12" is always going to be at greater risk of leaks than a roof with a steeper slope.

    -- Martin Holladay

  13. SwitchgrassFarmer | | #13

    I wonder if in this particular circumstance, with such a shallow pitch roof, whether a ventilated air space (cold roof) would be that effective? Is there going to be enough air movement to carry away any moisture?

    Perhaps this roof could be treated like a flat built-up roof with additional insulation added to move the dew point location away from the critical OSB layers of the SIP panels?

  14. GBA Editor
    Martin Holladay | | #14

    You're right that there will be less air movement in this type of air space if the roof has a low slope. That's one more argument in favor of roofs with a steeper slope.

    That said, I think that a 1-inch or 2-inch air space, with openings at the "soffit" and "ridge," would provide enough safety for a low-slope roof to let me sleep well at night (if the details suggested by Peter L were followed).

    -- Martin Holladay

  15. JohnStephany | | #15

    Here at Madison College Construction Program, we built using SIP's for years. There are some key things: being hyper vigilant when installing to make sure the gaskets are in the right place and in full contact. We threw out the hardware store gasket material the supplier sent out and went with a much more robust seam tape that expanded 2 times it original size over time. We then used the 3M tape that Martin tested on the interior as well, with a J roller. Also, I'm concerned about which type of roofing. Most standing seam roof metals cannot be installed on less than a 2 pitch. There are a few that are allowed on as low as 1/2 pitch, and they have robust gasket material inside the standing seam to stop leakage and are clear in their literature about the usage. At this point, you do need to remove the roof, and I would recommend a second layer of sheathing spaced off the first with 1x4 to create a vent space, on top of Grace Ice and Water shield, lapped 6" or more. And airseal everything on the interior as best you can. Good luck!

  16. Expert Member
    MALCOLM TAYLOR | | #16

    A comment on installing metal metal roofs in low slope situations:

    Apart from small penetrations for vents and roof stacks, all the other trim and detailing for conventional metal roofs rely on lapping material and more importantly gravity. Chimneys, ridge caps, valleys, gable, sidewall and eve flashing all need slopes to work. Further, unlike other common materials like asphalt, metal wicks water through capillary action, so on metal roofs water often travels uphill.

    This means metal roofing installed below 2:12 is inherently a much riskier assembly than on steeper slopes. Like SIPs themselves, there are ways to mitigate the risk, but these things are to mitigate risk that doesn't exist in other more robust assemblies.

  17. jackofalltrades777 | | #17


    Is 34.0 PERMS a pretty good perm rating compared to 30LB felt/tar paper?

    For my research the Europeans/Swiss have figured out the vapor systems long time ago and are ahead of the curve in some areas that US builders are not. SIGA makes some great products and knows that wood products need to breathe to allow for drying. They stop air/moisture from getting in but they are vapor permeable and allow moisture to dry out. Pretty advanced tapes, that's for sure.

    Grace peel & stick is used a lot and it works great as long as the underside of the OSB sheathing can dry out to an attic space. With that being said I have seen them install Grace P&S on roofs that were spray foamed inside the attic with closed spray foam in 5+ inch depths.

    Any moisture in the OSB will get trapped once the Grace P&S is installed. How much moisture does it take to create rot? I am not sure.

  18. GBA Editor
    Martin Holladay | | #18

    Peter L,
    34 perms is quite vapor-permeable.

    Determining the vapor permeance of #15 asphalt felt is tricky, because (a) each brand is different, and (b) batches from any particular factory are likely to be inconsistent, and (c) #15 asphalt felt is a "smart" retarder with variable permeance.

    In general, the vapor permeance of #15 asphalt felt is 0.5 to 6.0 perms when dry, and up to 60 perms when damp. For more information on this issue, see All About Vapor Diffusion.

    You're right that Grace Ice & Water Shield stops all outward drying, and is probably overused. That said, outward drying is impossible with many types of roofing, including asphalt shingles and standing-seam metal roofing, unless the builder includes a ventilated air space between the roofing underlayment and the roofing.

    -- Martin Holladay

  19. jackofalltrades777 | | #19


    So you would not recommend putting a metal roof, asphalt roof, or any roof WITHOUT an air channel on a SIP roof?

    Would a tall standing seam roof allow for SOME air ventilation?

    I talked with one SIP manufacturer and they stated that the whole SIP roof rot thing was overblown. They claim the climate (Juneau, Alaska) was the worst case scenario type of climate. They stated that there are thousands of SIP roofs without any vent channels and they have no issues.

    So who to believe?

    Why such confusion on the topic. If you look on the SIPA website, they allow you to install standing seam and asphalt shingle roofs directly onto a SIP roof, no air channel.

  20. GBA Editor
    Martin Holladay | | #20

    Peter L,
    Q. "So you would not recommend putting a metal roof, asphalt roof, or any roof WITHOUT an air channel on a SIP roof?"

    A. That would be my advice in cold climates (Climate zones 5 through 8).

    Q. "Would a tall standing seam roof allow for SOME air ventilation?"

    A. Not really -- although the old-fashioned corrugated types of metal roofing still seen in parts of Florida allow for some ventilation.

    Q. "I talked with one SIP manufacturer and they stated that the whole SIP roof rot thing was overblown. They claim the climate (Juneau, Alaska) was the worst case scenario type of climate. They stated that there are thousands of SIP roofs without any vent channels and they have no issues."

    A. The SIP manufacturers are correct about the climate in Juneau. It's damp, and there are few sunny days that allow for much drying. They are also correct that there are thousands of SIP roofs without any vent channels or rot. (Those are the SIP roofs that are perfectly airtight.)

    But I'm conservative when it comes to sloped insulated roofs. There are problems. Adding a ventilated channel above the SIPs is much less expensive than a future repair. It helps you sleep better at night.

    Q. "If you look on the SIPA website, they allow you to install standing seam and asphalt shingle roofs directly onto a SIP roof, no air channel."

    A. You're right. They do. But SIPA is an association with the mission of promoting SIPs. Historically, SIPA has downplayed the disadvantages of SIPs and highlighted the advantages of SIPs. SIPA is not the best source of information on potential SIP failures.

    -- Martin Holladay

  21. user-626934 | | #21

    "Q. "So you would not recommend putting a metal roof, asphalt roof, or any roof WITHOUT an air channel on a SIP roof?"
    A. That would be my advice in cold climates (Climate zones 5 through 8)."

    Martin, I would suggest that you extend your advice down to CZ4 (and maybe 3). We've seen some SIP rot down here in Virginia.

  22. GBA Editor
    Martin Holladay | | #22

    Thanks for your comments. GBA readers: Listen to John. Better safe than sorry.

    -- Martin Holladay

  23. user-626934 | | #23

    My advice for clients who come to me wanting to build with a SIP roof is always the same:

    "I'm confident that we can design an assembly that gets you the same or better insulation and air-tightness, is more robust, and costs the same or less money than SIPs."

    It's hard to argue against that, unless your brother-in-law owns a SIP fabrication shop.

  24. SwitchgrassFarmer | | #24

    Did some rainy afternoon SIP problem "Googling". A few references to Juneau and elsewhere but overall it seemed you had to drill through a number of search page results to find recent horror stories.

    Then I found this series of articles:

  25. GBA Editor
    Martin Holladay | | #25

    Thanks for the links to the stories about the $3 million SIP disaster in Portland, Oregon. I wasn't aware of that story.

    In case you missed it, here's a link to a GBA story about a residential SIP failure:
    A SIP Roof Repair in Wisconsin.

    -- Martin Holladay

  26. user-626934 | | #26

    Here's another one on GBA, via Bart Laemmel during 2016 BSC Summer Camp. See case study #2.

  27. SwitchgrassFarmer | | #27

    I missed the Bart Laemmel story, am significantly less GBA active in non-winter months. Thanks for pointing out that article John.

    Interestingly Enercept's Construction Guide (the article says Enercept provided the panels) has quite detailed recommendations for how to install SIP tape. The guide also has prominent notes that "A 6 mil. interior vapor barrier .... is required".

  28. jackofalltrades777 | | #28

    I went the SIP roof route because of the advantages that SIP roofs have (installed entire roof in 8 hours with 2 foot overhangs, instant soffit, low profile, air tightness, no thermal bridging, no attic). I used a polyurethane core due to the higher R-Value and fire rating (Class 1/ Class A). The SIP manufacturer also uses a T&G on seams/joints with a flexible gasket inserted on both ends.

    I taped the outside seams with SIGA WigLuv and then all the inside seams with SIGA Rissan. I then installed the SIGA Majcoat breathable membrane (34.0 PERMS). The final roof assembly was a metal roof that is elevated with sub-girts (1 inch).

    I learned a lot about SIP roofs and the pros and cons about them here on GBA. I believe if you take the belt & suspender approach, then roof should last just as long as a truss roof with an attic. Taking shortcuts and sloppy work on a SIP roof is not permissible as you will have problems.

  29. user-6527343 | | #29


    What would you recommend as an underlayment for a standing seam roof over an airspace on a low-slope roof (1/2:12). Siga Maj-coat is only recommended for roofs down to 2:12.

    Thank you.

  30. GBA Editor
    Martin Holladay | | #30

    You didn't mention vapor permeance, but it's worth emphasizing that the permeance of the roofing underlayment is irrelevant (because a standing seam roof doesn't allow any outward drying).

    I'm not familiar with the specification required for standing-seam roofing on a roof with such a low slope. My first instinct would be (a) to contact the manufacturer of the standing-seam roofing to see if they allow low-slope installations, and (b) to follow the recommendations for roofing underlayment provided by the standing-seam roofing manufacturer. Such a low-slope application may require a peel-and-stick product.

  31. user-6527343 | | #31

    Thank you, Martin-
    We have a SIP house under construction in Denver, CO. The roof consists of 10 1/4" SIPs with standing seam metal. The majority of the roof is an 8:12 slope, in which case I intend to follow the best practices as noted in this post (Siga Maj-coat for permeance and drying, then an airspace above, then the standing seam metal.)

    One portion of the SIP roof is low-sloped at 1/2:12. This is the specific area referenced in my previous question. I was hoping to build the same assembly as the 8:12 potions of the roof, but the Siga Maj-coat product is only recommended down to a 2:12 slope. Building code allows standing seam on low-slope down to 1/4:12 but does not address underlayment. The manufacturer does not have a specific product they recommend for underlayment. I can install a peel-and-stick product, but given the discussion around SIP roof problems, I was hoping for a product to allow for outward drying to the airspace.

  32. GBA Editor
    Martin Holladay | | #32

    In Comment #29, you said that the underlayment was being installed "over the air space."

    In Comment #31, you imply that the underlayment will be installed under the air space (between the SIPs and the air space). Which is correct?

    You won't get much ventilation drying from this air space if your roof is flat. Flat roofs are very tricky to insulate and vent. For more information, see Insulating Low-Slope Residential Roofs.

  33. simplifyIT | | #33

    GBA reposted this article from 2017. Great discussion points.

    Curious how this issue was resolved.

    I concur with others comments here re: choice of standing seam for such a low pitch, and wondering if the product selected was installed in accordance with the manufactures speciation for low pitch. Some metal roof companies make products specific to low-pitch installations.

    SIP's are a great choice, just need to be tentative to detail of installation as others have pointed out.

  34. Rick_Agro | | #34

    I have searched and searched and talked to a lot of people, but I have never seen a solution to a real bad Sip Roof. What is the best way to repair one that has a big problem, that I can feel comfortable will last. A major amount of my north side is shot.
    Thanks for all replies

    1. Expert Member
      MALCOLM TAYLOR | | #35


      The problem with rot in SIPs is that the sheathing layers are an integral part of the structure. If they have signifiant damage, you need an engineer to assess whether repairs are possible, or they have to be replaced.

      1. Rick_Agro | | #37

        Hi Malcolm,
        I agree with you that I need an engineer to assess the problem, I have not yet been able to find one to take on the task. I think I have talked to 5 that didn't think they could help me. the panel companies that I have spoken to are not willing to help and barely want to admit that there has ever been a failed panel. If you know of an engineer who will work in CT. I would love to have their name.
        Thanks for the reply,

    2. Expert Member
      Michael Maines | | #36

      Rick, unfortunately the solution is probably to replace everything. Here's a similar situation:

      1. Rick_Agro | | #38

        Hi Michael,
        I think I have seen every article about rot problems and sips, even in that article you mention, I wonder how the repair has held up long-term. Did the glue hold to the dirty insulation layer? Was the moisture problem solved? They did a repair, as have others, but did it solve the problem or just kick it down the road for a while?
        And by replace everything do you mean new panels?
        Thanks for the Reply

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