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exterior rigid insulation on a 1950s cape

user-181741 | Posted in Green Building Techniques on

Paul C. here, First I would like to thank all who take the time to answer these questions.
Would like to know if anyone has knowledge and experience with insulating rigid foam insulation on ex.t walls on an old house with minimal insulation in stud bays. I planned to install tyvek house wrap, 1″ rigid R-6 polyisocyanurate foil faced (John Manville) on 1×6 T&G , with vinyl siding will cause a moisture build which can start rot and mold? Certainteed tech support stated with this siding max. rigid thickness is 1”.
I have gutted the 2nd fl and installed full doomer and rear wall with 2×6 and have added 2×3 to existing 2×4 walls, R-23 rockwool in stud bays, roof is R-48. Ext. 1/2 CDX on doomer walls and existing 1×6 T&G, tyvek hose wrap, 1″ R-6 polyiso and Certainteed T-5 vinyl siding, installed Andersen 400.
Our home is a 1950s cape (1951 deed date), in NJ( please don’t hold it against me) zone 5, 2×4 wood frame with 1×6 T&G sheathing, stud bays have rockwool wrapped in resin brown paper ( Goldbond?) insulation (R-value?), 1/2”drywall interior. I am not planning to gut the 1st. fl. (time line we needed to move in) and have Certainteed T-5 vinyl siding straight edge sections to install on exterior to match 2nd.fl.. I am planning to remove old cedar shakes and replacing the old windows with Andersen 400.  Your Thoughts!!!

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Replies

  1. mr_reference_Hugh | | #1

    Would like to know if anyone has knowledge and experience with insulating rigid foam insulation on ex.t walls on an old house with minimal insulation in stud bays. I planned to install tyvek house wrap, 1″ rigid R-6 polyisocyanurate foil faced (John Manville) on 1×6 T&G , with vinyl siding will cause a moisture build which can start rot and mold? Certainteed tech support stated with this siding max. rigid thickness is 1”.

    Hello Paul C., I think that when you mention "experience" that usually relates to someone who idendifies and is obligated to address a problem with a wall assembly. Anyone who builds or renovates with a product like the one you plan to use can't claim (in my view) to have experience if they have left the project and never checked back after their work was completed. But another issue is that some problems can remain hidden in the walls for years before there is a visible failure.

    What I can share is what I know. I live in a house of your vintage. They are almost all built the same. The issue is that when you modify the wall assembly, you most of the time change the control layers. https://youtu.be/_JPkfIEYBBc

    When you change the control layers, you usually change the air tightness. If you change the air tightness, you often change the wall's ability to dry. You likely understand this because you are asking about potential mould.

    Because you have an older home, you would want an insulation with a high permiability rating that would allow the wall to dry. You would also want to include an air-barrier.

    Polyiso with a foil face would provide a good air seal if you tape it all up with attention to detail; however, it has a very very low permeability rating. This means that the wall cannot dry to the outside. In Zone 5 where you have a heating season, you dont normally want to intall a class 1 vapour retarder (vapour barrier) on or near the exterior face of the walls. I would opt for a 1" vapour open insulation like Rockwool Comfortboard or something that is more vapour open than foil faced insulation.

    https://www.rockwool.com/syssiteassets/o2-rockwool/documentation/technical-data-sheets/residential/comfortboard-80-non-structural-sheathing-continuous-insulation-techdata.pdf

    I would also suggest that if you are buying Tyvek that you look for the commercial version. It is thicker and tougher which reduces the risk of tears and other damage. Also put the least amount of staples in the Tyvek that you can because each staple creates a ... hole in the Tyvek. I hope you know how to create a positive lap and how to seal the the Tyvek with high quality tapes that the manufacturer says is compatible with their product.

    Hope this helps.

    1. user-181741 | | #2

      Thank you Hugh,
      I will look into your recommendations and ck on product availability. Would you have feed back on the tyvek stucco wrap for air barrier before comfort board? I have a suppiler that sells the pro 960/80 or pro 960/100 rockwool board ( commerical/industral product line) is this product more the is needed for home exterior insulation.
      I did watched Dr.Joe, very informative and a great resource going forward.
      Thanks again

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