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2″ foam board under exterior siding — what regulations?

GBA Editor | Posted in Building Code Questions on

I have 2″ Dow foam board that I want to apply to the outside siding of my building which is now covered in 0SB. The building inspector wants to know how this complies with Mass building code and what the requirements for the procedure are. Help!

To Typar or not, vapor barrier, nails or screws (and which kind), strapping or furring strip requirements, window and door treatment, etc. I have to spell it out for him and get the OK before I proceed.

Thanks.

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Replies

  1. Chris | | #1

    Hi Nancy,

    You might want to checkout the 2 threads below. I live in MA and had asked a similar question a few months ago. There is no shortage of opinions and variables.

    Depends on the type of siding you want to use. Windows "innie or outie?" Several other threads on the site with similar discussions. Just search for "rigid foam installation" and similar topics.

    The JLC has had several articles recently that illustrate installation details. Also, Green Building Advisor has a couple of great videos on Youtube. Finally, checkout some of the info on BuildingScience.com. I think they have a few articles that illustrate some of the detailing issues.
    https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/17543/cedar-shingles-directly-over-rigid

    https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/16743/cedar-shingles-directly-over-rigid

  2. Riversong | | #2

    Nancy,

    Sorry to be blunt, but if you're that clueless about how to insulate and finish your house with exterior foam, then you need a competent builder/renovator to either guide you through it or do the work (and apply for the permit). You can't simply learn this from reading articles or blogs if you don't have the basic knowledge of construction practices and building science.

  3. nancy marcus | | #3

    i am an owner builder and i have a right to build my own dwelling thank you very much. The builder who is helping me nor the building inspector of my town know the answer to this question anyway.

  4. nancy marcus | | #4

    and Robert, basically your saying that what you are writing is worthless since its coming from a blog and the internet

  5. Riversong | | #5

    Nancy,

    Actually you don't have an unconditional right to design and build your own home, except in rural areas where there are no zoning nor building nor fire nor sanitary codes.

    It has long been established that the community has a right to control or limit the placement, the height, the utility and road connections, and the safety and livability of a "private" home - because it has impacts on the broader community and on the future occupants of the building.

    That is why MA has a state-wide building code, in addition to local zoning, and that is why the building official has a duty to ascertain compliance. It is the responsibility of the builder, whether professional or owner, to document that the plans, materials and methods comply with code standards. If you don't have the capability to do that, then you need competent professional help.

  6. nancy marcus | | #6

    Exactly, i am looking for the code standard for mass. if your actually want to be helpful, point me in the right direction

  7. Troy Hodas | | #7

    Nancy,

    I commend you on your inititative. It's unfortunate because a lot of "real" builders aren't stepping up to the plate and building the high performance homes that are possible these days. 2" of rigid foam on the exterior can be a great technique. This all depends though on what climate zone you're in and what the rest of your wall detail is. What climate zone do you live in?

  8. Troy Hodas | | #8

    Ahh... Mass.. What are you doing with the rest of your wall?

  9. Riversong | | #9

    Nancy,

    I am being helpful. The problem is you don't like the answer to your question.

    The MA 1 & 2 Family Residential Building Code is at:
    http://www.mass.gov/?pageID=eopsterminal&L=4&L0=Home&L1=Consumer+Protection+%26+Business+Licensing&L2=License+Type+by+Business+Area&L3=Construction+Supervisor+License&sid=Eeops&b=terminalcontent&f=dps_780cmr&csid=Eeops

    But that document will not answer the questions you posed above. Those are questions about building methods that will comply with code standards. Methods of integrating exterior foam insulation, doors & windows, weather barriers and flashings are challenging to experienced builders. The code will not spell these things out.

  10. nancy marcus | | #10

    Hi Troy, thanks for your interest. The studs are 2x6 at 16 o.c. 1/2" osb over that with caulked seams. the interior insulation will be batt celulose or dense pack shredded paper and borate, still deciding about that.

  11. nancy marcus | | #11

    i am in zone 5

  12. Riversong | | #12

    Nancy,

    Cellulose insulation IS shredded paper and borate, and it doesn't come in batts.

  13. Brett Moyer | | #13

    Nancy,
    I'm going to have to agree with Robert. Exterior foam sheathing can complicate a wall assembly. If you don't understand the building science (physics)-- hydrostatic pressures, hydric redistribution, vapor profiles, air barriers vs vapor barriers-- you may want a consultant on the job. I acknowledge that most builders don't understand these issues either, but I'm sure there is an expert in your area that does.

  14. Mike | | #14

    i got to come back here for more of this - this is shapping up to be a good story and soap opera.

  15. nancy marcus | | #15

    I am sorry, i do sometimes mix up my terms. yes, expert advice is what i am looking for. Basically there has to be a standard or formula for my particulars which are not so unique that i need something designed just for me. i am interested in the recommendations that comply with the building code. For interior insulation i am planning on using the blue jean batt stuff or the dense pack cellulose. i already have 2x6 walls, osb, and caulking between the seams,and planning on a continuously running fan to deal with the moisture. I already own all the 2" r10 foam board that i need to cover the building so i want to use it. Yes, i have folks on my case that i am working with. I am not a scientist in building technology trying to write the code, just trying to find out what it is and follow it. Maybe it is not written yet. This is new for many people and even experienced licenced builders do not have the answer. So, where is the code for exterior 2"" r 10 published? This must be public information.

  16. nancy marcus | | #16

    My building feels like a sail boat of sorts, contolling the wind or the air, the oxygne and moisture, the light and the spirit. Pulling in and letting go, opening and closing, steering and driving it as we sail around the sun each day . Is this an art or a science or both? Its all very interesting to me and i want to understand it. I really appriciate all the feed back, i am getting more of an idea of how it works.

  17. GBA Editor
    Martin Holladay | | #17

    Nancy,
    I am not familiar with the Massachusetts building code, but I am fairly familiar with the International codes on which many local codes are based.

    Most building codes are fairly silent when it comes to siding requirements (or even siding attachment requirements). Siding manufacturers often have installation requirements, and these manufacturers' recommendations must be followed because codes call for builders to comply with all manufacturers' recommendations. So, step one: contact your siding manufacturer.

    Most building codes require a WRB, so you must be aware of which material (rigid foam? housewrap?) will be filling this role. Your WRB needs to be carefully integrated with your window and door flashing.

    Many building codes still have requirements for interior vapor retarders, so you should familiarize yourself with these requirements. You should also familiarize yourself with the debates concerning interior polyethylene, and why it is important not to use it.

    The first person to answer your question, Chris, gave you good advice. You may also want to read:
    http://www.interioralaskabuilders.com/construct/files/RemoteWall.pdf

  18. nancy marcus | | #18

    Okay. that was late at night. I meant as the earth turns around in space and we sail past the sun.
    Anyway, how does it go?
    From the outside in: Hardi board siding, vertical furring strips, nails or screws, two-inch insulation (R-10, no foil), OSB, 2x6 wall studs -- then what? and what size and type of each of these materials?

  19. nancy marcus | | #19

    thanks Martin, i will give Installing Exterior Insulation in Cold Climates a read. My insulation board is recycled and says Dow all over it, i did write to Dow and ask for instructions, waiting for a response, i will post what they say, may take a while to get in touch with the right person

  20. GBA Editor
    Martin Holladay | | #20

    Nancy,
    Although Dow may give you interesting information, the Dow product is not the siding. When I referred to siding, I meant a different product -- perhaps fiber-cement lap siding, or vinyl siding, or cedar clapboard siding.

  21. wjrobinson | | #21

    Nancy... you are close to getting the info you desire. Install the typar over the Dow, then strap and siding. Plywood is used sometimes to extend window frame out to edge of foam. Many window companies have pdf details at their sites showing window / WRB detailing. Typar site may have info.

    Journal of light construction
    Fine homebuilding

    Another site like this is greenbuildingtalk ... Dana1 is very helpful for what you are asking about.

  22. nancy marcus | | #22

    Hi Martin, dont like fiber cement or vinyl and cedar would be great but is too expensive, so i am going with hardi board, because the furring strips are vertical so siding has to be horizontal. otherwise i would prefer ship lap but i dont see how that can work. I understand the furring strips have to be verticle for any drainage or air flow behind. I am planning on staining the siding on the back side as well as the front.

  23. nancy marcus | | #23

    Is the typar truly necessary? I am planning on taping the seams

  24. GBA Editor
    Martin Holladay | | #24

    Nancy,
    I hope you have a chance to study some of the suggested materials (and explore the GBA Web site) soon.

    A WRB is necessary; Typar is one option. Some builders use rigid foam with taped seams (or seams with Z-flashing) as a WRB.

    No matter which WRB you choose, you must understand the implications of the choice -- advantages and disadvantages. A WRB must be integrated with window and door flashing.

    If you choose to use rigid foam as your WRB, you will usually be depending on tape (chemistry) for waterproofness rather than lapping (physics). Those who disdain the method say, "Physics always beats chemistry." (The question is the longevity of the adhesives in the tape.)

    Although you say that you don't like fiber-cement, you are choosing HardiBoard, which is made of fiber-cement.

  25. Riversong | | #25

    Nancy,

    Hardiboard IS fiber-cement siding. If you want real wood, then I would recommend spruce 1x6 pattern 105 drop siding, a well-draining type of shiplap that is thick enough to span the furring strips without deflection.

    Some builders are using taped foam board as the WRB (weather-resistant barrier), but that relies on tape adhering forever where you can't inspect it. An additional layer of housewrap, like Typar, is a sensible approach to long-term durability.

  26. nancy marcus | | #26

    for siding i mean the horizontal pine board that fits together, not sure what its called

  27. HDendy | | #27

    are you sure you want to be the builder...no telling what materials will show up to your site....

  28. Riversong | | #28

    Nancy,

    With all due respect, I already gave you the best advice anyone is going to offer: get a competent professional to either guide you through this process or, better yet, to do the work for you.

    As was evident from the start, you don't have the knowledge necessary to design or build a house. That's no judgement on you as a person. You may be a capable astrophysicist, but we are best served by using our strengths and not our weaknesses.

    If you don't know the difference between blue jean batts and cellulose insulation, or between HardiBoard and "the horizontal pine board that fits together", and if you think the building code is going to tell you how to detail your exterior wall system, then you certainly don't have the wherewithall to design or build something as complex as a modern house.

    Get competent professional help.

  29. GBA Editor
    Martin Holladay | | #29

    Nancy,
    If you do choose to follow Robert's advice, choose your builder carefully. Your answer to a previous question does not inspire confidence in your chosen builder: "The builder who is helping me nor the building inspector of my town know the answer to this question [To Typar or not, vapor barrier, nails or screws (and which kind), strapping or furring strip requirements, window and door treatment]."

  30. wjrobinson | | #30

    Nancy best purchase you could make in your house budget is a class here face to face with Robert ... or not .

    http://www.yestermorrow.org

  31. Riversong | | #31

    ADKJAC,

    I've already asked you not to speak for me.

    And I no longer teach at Yestermorrow because they've refused to become a smoke-free campus. I won't work at a place that doesn't put health and safety before profits or teach sustainability at an institution that doesn't walk its talk.

  32. nancy marcus | | #32

    Basically i am putting it together myself with friends and workers of different levels of skill, its happening so there is no point id depbating wheather or not i should do it myself, i am.
    Okay, its coming together, i am going to attach the foam board with furring strips, put the furring strips around windows and doors, put the ice and water shield over that, put the windows in over that , and then the siding. I will caulk and insulate any gaps or cracks. I was thinking about the window boxes but i dont think thats going to happen. and of course tape over the r 10 seams. Still thinking about the typar.
    Just dont know what length and type of screw or fastener i will use and if i should add washers. Ultimatly i will present this to the building inspector and he will either okay it or make corrections.

  33. nancy marcus | | #33

    in debating

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