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Insulated siding question

Aaron S | Posted in Energy Efficiency and Durability on

I am looking at building a home in southern Ohio. I want to use 2×6 walls with dense packed cellulose, drywall, Osb sheathing, tyvek house wrap, and progressive foam insulated siding. Does this seem ok as far as moisture issues / breath ability? Is it even worth it for energy savings to use the insulated vinyl siding? I like the thermal break that it would provide. I am very new at this so any advice is greatly appreciated. Thanks.

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  1. Aaron S | | #1

    Also, what is your opinions on open cell spray foam directly on the underside of the roof deck?

  2. John Klingel | | #2

    Let me ask you: Do you think that siding, which will let air all around it, is going to offer an appreciable amount of insulation? Consider plywood instead of OSB. Do a little searching here and you'll get your answer on the foam against the roof sheathing. (I think "not".) I did not see a vapor barrier in your list. Is that intentional? Search here for the story of the business that went belly up in S Ohio because they used vb's, and then the home owners ran air conditioning. (The problem may have been more to do w/ the brick (?) on the outside than the vb, but I doubt that you need a vb in S Ohio. Just air seal well.) PS: I am not a pro. My bother in law has been sheet rocking in N Ohio for 30 yrs, and never has seen a vb used on a house.

  3. GBA Editor
    Martin Holladay | | #3

    I'm going to disagree with John Klingel.

    First of all, I'm not sure why he gave you so much advice on vapor barriers, since you didn't ask any questions about vapor barriers.

    I see nothing wrong with your plan to install open-cell spray foam on the underside of your roof sheathing, as long as the foam is thick enough to provide at least the minimum R-value required by code, and as long as you spray the interior side of the cured foam with vapor-retarder paint. Consult with your local building inspector about local requirements for thermal barriers (to protect the cured foam from fire). You may need to protect the foam with drywall.

    If you want to prevent thermal bridging through your studs -- and I think it's a good idea -- you need thicker foam than can be provided by the insulated siding alone. For more information, see Calculating the Minimum Thickness of Rigid Foam Sheathing.

  4. Aaron S | | #4

    Martin, so you don't see a problem with moisture if I do use a fullback insulated siding directly on top of the tyvek house wrap? What about a "rainscreen"? I also understand your point on the thickness issue.

    As for the roof, as long as the foam is the appropriate thickness and the vapor-retarder paint is used, there shouldn't be an issue of ice damming or condensation on the roof deck?

    I didn't mention any interior vapor barrier because I don't plan to use one.

  5. Bill Bradbury | | #5

    Since you are using 2x6 construction, optimal value engineering can reduce sheathing costs significantly. Use 3/4" plywood for the sheathing that is still required and fill the rest of the wall with 3'4" XPS. Seal this layer as your air barrier, then I like the new rain screen house wrap for moisture management. I personally despise vinyl siding for many reasons, so I would also change your siding to something made of wood. A good compromise product is LP's SmartSide.

  6. John Klingel | | #6

    Martin: I said "I think not" because I was sure I read here, and elsewhere, that open cell foam on the roof sheathing was likely to let vapor through it, which would condense on the sheathing. Therefor, closed cell foam would be the thing to use. If I am mistaken on that, please advise. I only mentioned the vapor barrier in case he was considering using one. It seems that his environment is not a good place for one. If he is not planning on using one, then that is a moot point. Do let me know what the skinny is on the open cell foam, though, as I was sure it would not perform as well as closed cell. At any rate, I am glad I at least told him to search here, in case I was wrong. Apparently I was. Thanks. john

  7. GBA Editor
    Martin Holladay | | #7

    Q. "So you don't see a problem with moisture if I do use a fullback insulated siding directly on top of the tyvek house wrap?"

    A. Insulated vinyl siding is a relatively new product. It hasn't been installed for many years, so it's hard to know whether the use of thin foam will cause problems down the road. At least in theory, thin foam is much riskier than thick foam. That's why I always advise people to follow the recommendations in this article: Calculating the Minimum Thickness of Rigid Foam Sheathing.

    Q. "What about a rainscreen?"

    A. If you are using insulated vinyl siding, it makes no sense to install a ventilated rainscreen between the siding and the Tyvek, because the siding includes rigid foam. The rigid foam will only improve your home's thermal performance if it is installed tight to the sheathing. That's one reason why I'm not a big fan of insulated vinyl siding: the product eliminates the natural drainage and ventilation properties that make plain old-fashioned vinyl siding perform so well.

  8. GBA Editor
    Martin Holladay | | #8

    John Klingel,
    You're right that anyone installing open-cell foam on the underside of roof sheathing in a cold climate should spray vapor-retarder paint on the interior side of the cured foam.

    However, assuming that the installation is done properly, and the R-value is adequate, there's no reason that open-cell spray foam won't perform as well as closed-cell spray foam.

    That's why I think your comment ("I think not") was too absolute.

  9. John Klingel | | #9

    MRTIN/AJ: Thanks for clearing that up for me.

  10. Aj Builder, Upstate NY Zone 6a | | #10

    John, I wouldn't use open cell in a high moisture environment like a pool enclosure. But I have built with Icynene open cell sprayed with a vapor barrier. The home is the best energy performance home that I have been involved with. No moisture issues. And it does have insulated vinyl siding over tyvek too.

    Icynene now has a water blown mid-weight product that they seem to be pushing which may have the better attributes of both 1/2 and 2 pound foams.

    One more note here. I am all for building unvented spray foam roofs, but not usually unvented built up ridgid foam roofs. Why the difference? Spray foam adheres to sheathing. Ridgid foam has a capillary/moist air space by sheathing and in between sheets. These small spaces in many cases have caused several roof failures as documented here and at

  11. Tim Holt | | #11

    Hello, Aaron

    My name is Tim Holt and I'm Director of Product Development & Innovation at Progressive Foam Technologies, Inc. Here are some things for you to consider about using insulated siding that are based upon extensive 3rd-party research and rigorous industry evaluation:

    1. can use insulated siding in your wall assembly. It will deliver the energy savings expected from any exterior insulation product with the same R-value and improve the moisture management capability of your wall assembly.

    2. Fullback siding insulations are not new products. They have been in use for over 20 years in both new construction and remodeling, are compatible with any type of siding, and have been thoroughly evaluated by industry experts.

    3. Insulated siding is recognized in the 2012 International Energy Conservation Code and in Energy Star Version 3 as an exterior insulation product that can be used to meet wall assembly R-value requirements and thermal bridge reduction requirements.

    4. When the R-value of an insulated siding product is below the requirement of a specific wall assembly, it can be used in combination with a layer of insulating sheating to achieve the total R-value requirement.

    5. Fullback insulation products and insulated siding have demonstrated the ability to keep wall assemblies and components dry over time. This has been the conclusion of a two-year, comparative, moisture monitoring study at the NAHB Research Center where insulated siding of R-3 was installed over OSB and a weather-resistive barrier.

    Hope these facts help with your decision and would be happy to provide further technical information at your request.

    Best regards,

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