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Retrofitting Walls Without Sheathing

Ahugg | Posted in General Questions on

Hi all, I’ve spent hours trying to research and have found a couple questions on here to be of similar nature. But they are older and not many people chimed in.

So here it is…house is 34 years old in northern Wisconsin.  I have no wood sheating on my exterior walls.  Just studs, then 1 inch foam board and aluminum siding.  I am doing a complete exterior remodel with new windows, siding, roof, soffit and fascia.

I cant stand the idea of no sheating on the house.  Too many entry points for mice, bugs and whatever else.

I’ve had several contractors over for getting estimates on the job and they all want to put 1/2″ osb over the foam board.  House wrap over the osb and then new vinyl siding. None of them expressed concerns of any sorts.

Is this acceptable and standard practice? Anything to be worried about at all?

Thanks for any comments and help with this.

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Replies

  1. Expert Member
    ARMANDO COBO | | #1

    It's not approved by code. There are a handful of insulated sheathings on the market which have been approved with ICC-ES reports. You could also hire your own engineer to give you a report to submit to your Building Dept.
    The most common practice, and the one I use always, is taped rigid foam on top of taped OSB/Plwd sheathing.
    Here are some additional sources of information:
    https://basc.pnnl.gov/resource-guides/continuous-rigid-insulation-sheathingsiding
    https://www.buildingscience.com/sites/default/files/migrate/pdf/GM_Guide_Insulating_Sheathing.pdf

  2. Expert Member
    Akos | | #2

    You have to check what is providing bracing in your house. If the bracing is handled elsewhere (let in bracing or corner brace with plywood) the sheathing on the outside is not structural, you can do pretty much what you want.

    The issue you run into in your cold climate is that 1" of rigid is not much R value. This could be fine if you have a warm side vapor barrier, but if you are missing it, it can create condensation issues. The fix for this is a bit more foam, in Zone 6 you need R7.6 total on the exterior so maybe another 1/2" or 3/4" more.

    Make sure they also protect the bottom/top and sides of all exposed foam. These areas are prime targets for critters.

  3. capecodhaus | | #3

    Why not take this opportunity to do things correctly and remove the foam sheets and install new plywood, osb or Zip wall?

    Do you have any insulation in the walls?

    I don't see the appeal of having a strangely assembled home. Especially if it defies code compliance, and could negatively affect resale value and/or bother you til you lose a portion of your sanity.

    1. Expert Member
      Akos | | #4

      I'm of two minds on this. In some ways I agree with you, now is the easy time to do it, but taking the foam off means all that foam is going to garbage.

      Assuming the building is already braced to code, the extra bracing is not required, so why add more? Maybe if you are in seismic or high wind area, it would be worth it.

      One way to look at it is if the OSB over the foam nailed out with a tight pattern will still provide WAY more structural support than the foam ever did, so you are still making the building significantly stronger than what it was. With older houses that is still a pretty big improvement.

      1. capecodhaus | | #5

        Im curious is there any insulation in the walls? Im assuming there is.

        This house is from the mid 80's with no sheathing and has exterior insulation that is also inadequate for its northern climate. It just seems like an odd approach to what is probably a typical house in northern Wisconsin.

        Maybe the best approach at this point would be to access the stud cavities of the exterior walls from the exterior, add new batt insulation, sheath the walls new, etc, etc..

        I suppose the old foam could be removed and donated locally.

  4. Ahugg | | #6

    Thanks for the replies so far guys. So from my knowledge, there is batt insulation in the wall cavities. I should have mentioned that in my original post. I did also see a vapor barrier behind the drywall when patching a hole one time.

    As far as bracing, I don't know if there is any, but every contractor has said they would pull the foam off at corners to make sure there is. I dont have any reason to believe there isn't....mainly because the house made it this many years with no structural problems that I'm aware of.

    So...I have a vapor barrier, studs and batt insulation, and the foam board. Should be adequate insulation considering most houses only have the insulation in the wall cavities.

    Also, most contractors have mentioned they would be wrapping coil stock on the underside to protect osb and foam to seal it from critters.

    This project is consisting of siding/sheating house wrap, windows, soffit, fascia, and a new roof. So in other words a very expensive project. All contractors I've had over have a reputation and presence in my smallish city. None have been a pickup truck type contractor that wont be around a year from now.

    I bet there is few amount of houses in my neck of woods built the way mine has. I think most contractors will be discovering this in the next 10 years when that time will be coming to do exterior remodeling.

    Assuming and of course veryifying that there is some sort of bracing, is there a consensus that everything should be fine?

    1. capecodhaus | | #7

      Im not going to make a final determination. Im not comfortable with it, it seems like a backward assembly. My ocd is kicking in.

      Is the rigid foam in good condition?

      Has the rigid foam shrunk in size over the decades and now have gaps between?

      Plan on giving them some attention and time such as spray foaming cracks and crevices, and replacing anything chewed up by critters. This may be one of those projects that you don't know what you're getting into until the contractor discovers.

      It's probably fine and once the work is done, who would know anyway.

      1. Expert Member
        Akos | | #8

        Continuing with James' points. Two important items to pay a lot of attention to: your air barrier and your water barrier.

        The air barrier can be either at the foam or sheathing layer. The simplest is taping (with a quality tape) the seams of the foam or OSB as well as taping to your foundation and the top to your wall top plate. Getting this detail right is the simplest and biggest energy improvement you can make to your place. Some tapes to the foundation need a special primer, make sure the tape and this is on the jobsite before they start. If you are into DIY, this is something you can easily tackle, it is a job that does take some attention to details but also very satisfying.

        With the OSB on the outside and new windows, the water barrier is pretty straight forward with standard house wrap. Make sure the rough openings are also flashed properly all the way out to the new WRB with some flex tape. This is easy to do now, but very hard to fix down the road.

  5. capecodhaus | | #9

    My conservative thinking say stay away from any type of unusual building assembly in ordinary residential housing.

    If I was in your position I would consider replacing stud cavity insulation with new batts and a new layer of wall sheathing to the studs, from this point onward it's straight-forward construction process. I just wonder what the 1980's batts look like, probably full of dust and junk from air infiltration due to the foam boards not being a tight assembly.

    Option two, leave any existing cavity insulation in place, add a layer of plywood sheathing to the studs and wrap that with 2 inch rigid foam. Contractors like working with new materials, they are cleaner and more true to form yielding better results faster.

    Like it's been said by others above, defining the exteriors air/vapor barrier as well as managing bulk water intrusion is paramount, done incorrectly will result in many failures happening simultaneously.

  6. Ahugg | | #10

    Here's a couple and only pictures I have. I had a roof leak and attempted to try and fix. (Didnt work) There was no red tape on the seams, we added that. When taping seams, is it neccessary to tape both foam board seams and the osb that would go over foam?

    I imagine the other gable wall on other side has the osb as well. I'm guessing that's the only osb on house.

    Foam board seemed in decent shape. That part of house in picture though is the WNW side. Maybe the south side might be in worse shape.

    As far as tape on the foundation, contractor mentioned coil stock wrapped around bottom. Not exactly sure what he meant by that. I imagine you would tape the top of that to the osb though?

    Dirty or dusty batt insulation isn't a problem is it? As long as it's just dirty from air and not moldy or anything?

    I cant imagine how much extra it would be to tear everything off and put everything back on. Right now the project is at 46k. My wallet is hurting.

  7. Andy_ | | #11

    I've got to ask...what's the point of all this work? What I mean is, what problem are you trying to solve here?
    Is there evidence of structural deficiencies or you just have a gut feeling that foam and bracing isn't good enough?
    Is the temperature of the house that uncomfortable? I mean, $46k will buy a fair amount of vacation time in the sun or a few mini splits and solar panels.

    1. Ahugg | | #12

      To seal it up better. Keep the mice out. All work is getting done regardless if we do sheeting or not. Lots of lose siding that I cant just snap back in. Leaking roof, leaking windows (Air)

  8. capecodhaus | | #13

    Ahugg,

    If the foam is in good condition and you don't want to make this into a bigger job, consider skipping the layer of plywood. Deleting the plywood sheathing will likely result in considerable savings to your project.

    Focus on applying tape to all joints on the foam sheets, working from bottom of wall to top. Seal the foam carefully at the junction of foundation and wall framing and at top of wall. Add fasteners to the foam panels if they are poorly attached to the wall frame before applying tape. Research the correct tapes to use for concrete to foam and/or foam to foam adhesion. You likely be using two different tapes.

    For more protection from critters, at the base of the wall, consider applying a band of peel and stick Ice and Water Shield to the foam sheets around the perimeter of the house and lap it over the foundation. You may need an additional tape band to seal the Ice and Water Shield to the foundation. Ice and water shield is a thick, impervious membrane and should keep most critter out. You'll also want to cover this up for aesthetic reasons with trim/siding. This would replace the coil stock (sheet metal) your contractor mentioned installing but didn't mention how, if at all, he would seal it tight to keep critters out.

    At the junction of the lower roof and the upper gable wall on your house is also a good place to apply a band of Ice and Water shield, most roofers should know this, most don't do this.

    Once all the foam sheets have been firmly attached, taped properly and Ice and Water shield applied, cover all this with a layer of house wrap such as Tyvek/Typar. Apply the house wrap, horizontally from bottom of wall to top of wall. All builders should know how to incorporate this into your window openings and properly flash this layer of waterproofing in preparation for window and siding installation. Taking extra time and money to tape all seams of the house wrap layer will benefit your cause. Use the appropriate tape again.

    In order to install siding to a house with no plywood sheathing, assuming its clapboard or vinyl siding, the installer will need to nail the siding carefully thru the foam into the studs otherwise the siding will not have solid attachment.

    Good Luck

    1. Expert Member
      Akos | | #14

      I've haven't had good luck sticking Vycor to vertical surfaces. Even when primed, it takes a lot to get it to stay without something clamping it down.

      I would use something specifically meant for sheathing to foundation joint. This would be Zip Liquidflash or Wigluv+Dockskin.

      I don't trust critters not chewing through tapes and foam. If you want a real critter barrier, you need wood or metal, even better, metal over wood.

      1. capecodhaus | | #15

        Akos,

        I agree, Vycor doesn't adhere well to many surfaces in construction and I wouldn't recommend it. If it gets wet it tends to peel back on itself.

        The contractor should put metal coil stock over the foam but most importantly that foam should be sealed to the foundation with something durable and impervious, like a peel and stick membrane or similar. I shouldn't have said Ice and Water Shield perhaps. I don't believe the contractor involved was planning to take this extra step is the most concerning part and the homeowner seems to want to avoid making this into a bigger project which also hurts final results.

        If I could only choose one solution and it involved coil stock loosely attached to reduce critters versus a well sealed peel and stick membrane barrier, I 'd pick the peel and stick membrane that is appropriate for the surfaces. Especially if the grade is a good distance from the lower course of siding. Applying insecticide around the perimeter foundation and you shouldn't have critter issues anyway.

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