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Community and Q&A

1980s vinyl siding and exterior insulation

tadumbleton | Posted in Energy Efficiency and Durability on

I recently bought out of foreclosure a 1982 modular house in upstate NY (climate zone 6 but on the edge of 5).  The 2×4 construction is in decent shape, but I want to upgrade the thermal envelope and convert the electric heating to a mini-split.  I’m replacing all of the interiors and I’ve demoed out all of the sheetrock and pulled out the pink insulation.

I’ve been reviewing the various options for the thermal envelope upgrade, and as I am planning to replace some or all of the existing windows it seems that perhaps the best way to upgrade the envelope is a layer of exterior insulation.  This requires me to replace about 1000SF siding which is an unfortunate cost, but it will let me add some curb appeal to a currently beige house.

The cheapest version of the exterior insulation is a layer of PolyIso ($.50/SF), then Roxul comfortboard 80 ($1.11/SF) ,then Zip R ($1.43/SF) then Gutex Multitherm ($2.72/SF).  The Zip R includes also the WRB and means I won’t have to install furring strips which is simpler.

So while there is a 5x delta in the material costs of these options, the overall cost will be more impacted by the labor associated with the install than anything else.

What I am concerned about is that if I replace the existing Vinyl with new Vinyl it seems that I’m limited to 1″ of exterior insulation under the vinyl, and that I can’t install it over furring strips.  Is this correct?  If I’m replacing the sheathing it seems to me I should really do as thick insulation as I can since the material cost is not the driving factor.

Does anyone have thoughts or experience with Vinyl?  I’m going to price hardy board, but budget will likely dictate…  Thank you for any thoughts and experience.

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  1. GBA Editor
    Martin Holladay | | #1

    The first point you need to understand is that there are rules concening the minimum R-value of exterior rigid foam. If you plan to install rigid foam on the exterior side of 2x4 walls in Climate Zone 6, the rigid foam needs to have a minimum R-value of R-7.5.

    For more information, see "Calculating the Minimum Thickness of Rigid Foam Sheathing."

    Concerning the installation of vinyl siding over furring strips: Plenty of people have done it, but doing so often violates the manufacturer's installation instructions, and therefore voids the warranty. For more information on this issue, see "Can Vinyl Siding be Applied Over Furring Strips?"

  2. tadumbleton | | #2

    Thank you Martin,
    Yes I was vaguely aware of that constraint and my goal would be to add more than R7.5. It seemed to me that the Zip sheathing and the Gutex would give me a smooth exterior for the vinyl installation if that was going to be required. I'm trying to think thru all of the options since I'm not planning to do the exterior work myself and I'm speaking with several contractors who I am expecting are going to have different preferences which I will have to work with. I guess we will see...

    On another note - Since I have already demoed the interior, and since the winter is coming and the exterior might not get done till the spring maybe you can advise on the best approach to insulate the interior. I want to do this now so maybe I can get a little temp heat in the house to let us work more comfortably thru the winter. This I would do myself and I was thinking to use mineral wool batts. Do I need to do any air sealing before I add the batts? I'm not demoing out the ceiling or any of the attic insulation (I will add more, but not remove what is there). I was looking at maybe using intello membrane, but I don't know how I can use that since I'm keeping the existing sheetrock ceilings (they are low at 7'-6" AFF). I hope that question makes sense.

    Regards, Tim

  3. GBA Editor
    Martin Holladay | | #3

    You can choose from a wide variety of insulation materials to install between your studs. Installation quality matters more than the material you choose.

    Regardless of which type of insulation you choose, you need a well-defined plan to address air leaks. If you want to delay the installation of your air barrier until the exterior work is performed, that's possible. (Many builders used taped exterior sheathing as their primary air barrier.) You should know, of course, that your walls will continue to be leaky until you get around to installing your air barrier.

    If you want to address air leaks from the interior, one possible approach is to install open-cell spray foam between the studs. (In your case, open-cell spray foam is better than closed-cell spray foam, since open-cell spray foam works better with exterior rigid foam than closed-cell spray foam. Open-cell spray foam allows a wall to dry to the interior.)

  4. tadumbleton | | #4

    Martin - thank you for your response. I am meeting exterior subs and looking to find someone who seems like he can bring a big team and also who understands the goal (maybe not easy?!). Perhaps if we use less expensive insulation I can afford better siding, or maybe I will use the Zip-R so I can have a flat surface for cheaper siding (vinyl).

    RE interior insulation - I am hoping that because the house is a modular that the studs are pretty evenly spaced so mineral wool will fit nicely, but I will buy some and see how it goes and if it's a problem I'll switch to fill.

    For ERV I am looking at those Lunos models, but wish they were cheaper... I think I need 6 of them which is 3,400 for the units alone. That seems like a lot for such a small house.


  5. Expert Member
    Dana Dorsett | | #5

    In most of upstate NY you can get 2" reclaimed roofing polyiso for about 30-40 cents per square foot. Many foam reclaimers advertise here:

    This outfit is selling factory-seconds foil-faced 1.5" (R9-R10) for less than 50 cents per square foot.

    Every pair of Lunos e2 is good for 22 cfm. How big is this place?

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