Ask Todd Miller *Metal Roofing Expert

Structural Insulated Panels

Written by Todd Miller on August 31, 2009 | Filed under: Misc,Roofing Answers,Roofing Installation

Q: We are building a home with 8″ structural insulated panels (SIPS) for the roof decking (9/12) and want to use a Fabral SSR roof on top. As an engineer, I know the value of ventilation, but when asked, the roof & SIP manufacturers point at each other and say, ‘whatever he says’. Do I need to spend a fortune to build up a secondary decking system with lathe on top of the SIP for ventilation, or can I slap the metal directly on the SIP (with ice shield)?

A: Great question. In my experience, if you have a vapor barrier on the bottom side of the SIPs and if the joints between the SIPs are properly splined and sealed to prevent moisture migration, you should be fine.

There are, though, as an option, some SIP panels with built-in ventilation grooves. You could consider those as well.

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21 responses to “Structural Insulated Panels”

  1. Todd Miller says:

    That is certainly a good way to go. You would need to install either decking or horizontal battens on top of your vertical battens, in order to have something to secure the metal roof to. Make sure that the metal roof you install is approved for installation over battens if you go that way. That said, if the SIP panels are completely sealed off so that moisture from inside the home cannot migrate into them, I am not sure you need to do more than just underlayment and then your roof. There are certainly many applications like that functioning just fine. The keep is keeping moisture out of the SIP panels and out of the joints between the panels.

  2. Bryan Schanze says:

    We are in the permitting process of building a Sips home in eastern Kansas and would like to have a metal roof. This area can have very high humidity most of the year and many days of temp swings of 30dg.. The hvac system will include a air exchanger to help control humidity. So if I understand the previous post we need to start with a breathable underlayment, then vertical 2×4 furring strips followed by ridge venting? Could you outline a recommendation. Thanks!

  3. toddmiller says:

    I would suggest a vapor barrier someplace in the system, as close to the living space as possible. However, if I am understanding correctly what you have, I believe the amount of insulation will help prevent condensation and also ice dams.

  4. Regas K Halandras says:

    We are in NW Colorado @7000′. We will be adding @5″ polyiso with 5/8’s osb over an existing, insulated conventional roof. We are unsure of that R value. We had not planned on building a cold roof under the new steel roof. The roof underlayment will consist of high temp ice & water and triflex synthetic underlayment.

  5. eric coleman says:

    Confusing contradictions on the solution……..Sip on solid original sheathing and rafters, plus 2: ventilation space, plus new sheathing, moisture barrier, and steel not enough??

  6. Stephen Dunsmore says:

    Anyone who thinks their metal roof problems will be solved by putting asphalt shingles up is dreaming. The first thing to know about the asphalt shingle product is that there is zero warranty. Right now there are huge class action lawsuits against the biggest companies and even though BP is supposedly agreeing to pay some money (basically it is usually enough to remove their faulty product) they are not admitting the product is flawed. I have a “lifetime warranty” Architectural Shingle roof over SIPs which is shot after about five years and needs to be replaced. My contractor has the same failing roof on his non-SIP roof and says even he can’t get anything from BP. Think of what asphalt shingles are made of and then think of steel or aluminum in comparison. Which one do you want between you and the elements. The whole “hot” roof and “cold” roof discussion is just a distraction and excuse from roofing manufacturers as an out for them to evade their own warranties. SIP manufacturers need to stand up for their customers and back their own product instead of suggestion that you need to build and second, entire roof over their roof to protect their product. How many layers are needed? I have eight inch SIPs. Put 2x4s on top of that and my roof is over 9-1/2″ thick before laying down what? 1/2″ or 3/4″ of more plywood? Then a metal roof with 1″ ribs? Maybe we could throw in another “intermediary” roof on top of the second roof for real protection? How about putting a 6″ SIP on top of 2x4s on top of the 8″ SIPs as further insurance? At some point the roof has to stop and the roofing needs to start. My house has a vented crawl space because some moron believes that hot, moist air is somehow going to blow cold moist air from my basement and mandated those useless vents which I can now close off because the house is built but that same moron is unable to come up with a way of putting roofing materials on top of building materials so that the materials won’t fail and the manufacturers have to stand behind their advertised warranty.

  7. toddmiller says:

    Thanks Ken. That is some great input and so good to hear from someone who is out in the field with these products.

    Many metal roofs are applied over decking without “sleepers” or battens (but with underlayment). That practice has been done successfully for many years on thousands of metal roof installations.

  8. Ken Toman says:

    I have worked with sips over 20 years, we have learned quite a bit regarding ventilation. What you have to keep in mind with metal roofs. Is that the panels should be looked at as one layer of OSB. Therefore when applying a metal roof, you should always mke sure your have a good vapor barrier applyed, and 1 by four sleepers applied every four foot horozontally . Remember, it would be just like applying it to one layer which is only 7/16 th. The seams on the sips should be taped on the exterior of the sips if you are south of the Mason Dixie Line, and on the interior of the sips, North of the Mason Dixie Line. Any roofer who applies a metal roof over a sip without sleepers, has not done his homework.

  9. Jason Mihalick says:

    Todd, we are in the process of fixing our roof now. So far the SIPs have been solid except in areas where the metal roof leaked (fault of the initial installer). We are fixing as I described in my “June 4, 2014 at 9:00 pm” comment. If you want to chat about it for purposes of a case study, please send me an email.

  10. toddmiller says:

    Certainly I’d be happy to talk. My office number is 1-800-543-8938 ext 201. Feel free, too, to email me and we can set up a time via email to talk on the phone. I can be difficult to reach. My email is

  11. Val Stewart says:

    Would there be any way I could contact you via phone, we have a three piece vaulted ceiling modular with some serious sip panel roof problems and could really use some advice. Thanks

  12. toddmiller says:

    If you have any rotted lumber now, it probably needs to be replaced. If you can provide good sealant from the inside, you probably can correct things to avoid future problems. The standing seam roof, if installed direct over the outside decking on the SIP panels, will drop their temperature a bit and increase the chance of dew point being reached. For that reason, good sealing which prevents moisture from inside the home reaching the outer decking is very important.

  13. John says:

    Yeah. I don’t even know what to say here. I built a home that is utilizing sips but I’ve not installed the roof, yet. And I’m not sure the route I should go. The sip installer, although recommended by the manufacturer, did a terrible job of sealing so I am going back through the interior side sealing them, especially in the valley areas.

    What I’d like to know is IF I can adequately seal these areas WHAT is the preferred way to eliminate the dry rot. I’ve read elsewhere that a cold roof doesn’t necessarily eliminate the problem(s) but I’m not sure it that is because there were still issues relative to caulking and foaming, etc. My intent is to install a metal standing seam roof.

  14. John says:

    Yeah. I don’t even know what to say here. I built a home that is utilizing sips but I’ve not installed the roof, yet. And I’m not sure the route I should go. The sip installer, although recommended by the manufacturer, did a terrible job of sealing so I am going back through the interior side sealing joints, especially in the valley areas.

  15. toddmiller says:

    Thanks, Jason. That all makes sense. The breathable underlayment we sell is RoofAquaGuard BREA.

    Please email me at if you’re interested in more information or pricing.

    Thanks and please contact me anytime.

  16. Todd, thank you very much for letting my comment through and for your condolences. There actually is an underlayment under the metal on this roof – 30# felt. (There is also 15# or 30# felt under the warm side of the panels (over top of our tongue and groove wood ceilings on the interior) It’s just hard to tell from the photos because of the rust and oxidation stains on the felt. We are yet to open up the whole roof and see what we have, but I will say at this point that I think the felt has done it’s job and helped protect the SIPs to the extent that it could. When walking the roof, I have yet to discover what I would consider soft spots (and I have been over most of this roof myself). For the one panel that we opened, the SIPs appeared to be in acceptable condition and still should hold fasteners.

    The more research I have done, the more I see folks recommending furring of the deck on the SIPs. E.g.,

    What are your suggestions for a breathable underlayment? At this point I am considering using GAF Deck Armor.

  17. toddmiller says:

    I am so sorry for what you have gone through. While very painful for you, your job is a good case study. I am really surprised that it looks like there was no underlayment beneath the metal roof panels. That is very much in violation of building codes. I am also in Ohio. Should you want to re consider a metal roof, or should you be seeking a source for breathable underlayment, please let me know. I can be reached at

  18. We had the same problem with installing standing seam galvanized roof panels over top of our SIPS. We will be replacing it this summer or fall after only 13 years on our “lifetime” metal roof. We are going to tear off all of the galvanized metal roofing and felt underlayment. Then we will apply a new layer of breathable underlayment, followed by vertical furring strips (probably 2×2 or 2×4 16″ on center), followed by a new layer of sheathing, and then another layer of breathable underlayment. All of it will be ventilated at the facia and ridges. As much as we like the look of metal, we are tired of dealing with snow and ice issues on the roof here in Ohio, so we will likely resurface the new roof with asphalt shingles which hold the snow better. Shingles should cost quite a bit less too, which is appealing when considering the extra expense we are incurring for the tear off and new layer of sheathing. We are not happy at all because 13 years ago we were told that the SIPS would not require ventilation. Great theory, but not the reality. I think the reality is that as the home ages and the OSB skins on the panels expand and contract, previously airtight foam joints slightly open up and allow for warm air to escape the system and thus condense on the first cold layer. In our case it was the back side of our galvanized roof panels. See pictures at

  19. toddmiller says:

    A cold roof is when a chamber is built to create a roof above / on top of the existing roof. The resulting chamber is vented with fresh air intakes at the bottom and exhaust at the ridge. Typically it ill have a depth of 2 – 4″.

  20. Ruby Mayes says:

    what is a cold roof system? We are going to put a steel roof over our SIP roof panels but I don’t know what a cold roof is.

  21. Karen says:

    We built our timberframe home with sip panels 7 years ago. The roof has sip panels. Not long after building we noticed our downspouts filled with granular crystals from the roof and the shingles were curling. We put the roof right on top of the panels with ice guard underneath. At home shows we started questioning roofers about our situation. We bit the bullet and installed a metal roof last year. When they were tearing off the shingles they saw evidence of the start of dry rot on our sip panels. They took pictures and showed us. We put in a cold roof system under the metal roof. If you have a sip roof or are putting one on, please research, research, research before applying the shingles directly on top of the sip panels with no venilation. Our metal roofer told us we were third homeowners with sip panel roof to contact him with this problem. One homeowners roof was 12 years old and in quite serious shape. Most sip panel manufacturers dance around this question of venting or not to vent. Please check this out throughly so you don’t end up replacing a roof only 7 years old like we had to do to head off serious problems down the road.

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About Todd

Todd's expertise comes from his years of experience in metal roofing manufacturing. As president of Isaiah Industries, based in Piqua Ohio, Todd runs a several of the world’s leading manufacturers of residential metal roofing; Classic Metal Roofing Systems, Kassel & Irons, and Green American Home. His personal goal is to educate homeowners of the long-life benefits of metal roofing.

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