Replies

1. Expert Member
   BILL WICHERS | Mar 14, 2022 09:32am | #1

   High R value won't make your wall 'cold', and won't increase the risk of mold by itself. As long as your wall can dry in both directions, you won't have any problems. Where you can run into trouble is if you have a vapor barrier on the exterior, or if you have insufficient exterior rigid foam to keep the sheathing warm enough to avoid mositure problems within the wall.

   If you're worried, put up a smart vapor retarder (although that will probably be more difficult with a wet plaster wall) to limit the amount of moisture that can get into the walls in the winter.

   Bill

1. 
   Cleanair | Mar 14, 2022 10:22am | #2

   Yes Sheetrock just went up as well as plaster. I guess I’m going to have to seal the wall openings well from the inside and control as much moisture as possible.

   As far as vapor barrier Inused ZIP half inch board. The only vapor barrier is the green coating. I did ZIP liquid flash all nail holes, corners, wire protrusions, and beam penetrations. Thanks for responding.

1. Expert Member
   BILL WICHERS | Mar 14, 2022 12:29pm | #4

   The green coating on the Zip panels is a WRB, a Water Resistant Barrier, but it's still vapor open, so it's NOT a vapor barrier. That makes it like housewrap, and it still allows for exterior side drying which is a good thing.

   You do want to try to keep your air barrier intact on the interior though, which means sealing up any penetrations like electrical boxes in the walls, and wire/pipe holes in top and bottom plates. Air leaks can transport a lot more moisture than you'd expect.

   Bill

2. 
   jberks | Mar 14, 2022 11:45am | #3

   Cleanair,

   Try not to mix up condensation formation and mould as a direct corollary. Mould needs very specific conditions to thrive. Based on what you said, it sounds like your wall assembly is able to dry to the inside.

   Perhaps you might get some condensation on the backside of the sheathing in the winter months, but increased vapour drive from sunny days and (hopefully you've planned for) good ventilation/humidity control on the inside should allow the vapour to dissipate inside and keep the wall dry.

   PS. Just my opinion, I'm a nobody, I'm basing my thoughts off a bit of hands on experience and this BSC article:
   https://www.buildingscience.com/documents/digests/bsd-controlling-cold-weather-condensation-using-insulation

3. 
   gstan | Mar 14, 2022 01:10pm | #5

   How much is peace of mind worth? A whole house dehumidifier will preclude potential problems but it will cost you(Initially, and in Maintenance, and in Electricity) or you can find out the hard way after living there a while.

4. 
   walta100 | Mar 14, 2022 01:37pm | #6

   I do not think you will have a mold problem in your wall as long as all the insulation is cover with drywall or some other air barrier that will stop warm moist air from moving thru your insulation. Covering your walls with something like bead board and skipping the drywall could be a problem.

   I think it is a good idea to operate a dehumidifier in a newly constructed home starting just after the last window and doors are installed and for the next 12 months. After 12 months you will dried out the tons of construction materials and should not need the dehumidifier unless you have a huge moisture source that you would be better off addressing directly.

   Of course, you know not to install any vinyl wall paper on any exterior walls.

   Walta

5. 
   Cleanair | Mar 25, 2022 05:55pm | #7

   Walter. I do have kitchen cabinets on the outside wall. That wall gets full afternoon sun in the winter time so there is that. We elected not to do a backsplash just for the reason to give it some air movement to the interior.

   The crawlspace will be encapsulated and dehumidified. The garage will not be conditioned but I do have the option for a mini split.

   In my zone 4 do walls dry to the interior or exterior?

   I also did all of the reccomended sealing outside including removing nails in stud cavities, sealing nails with liquid flash. Taped all joints.
   House will be dehumidified.

   Thanks for replies to this question I’m worried about the potential issues here.

1. Expert Member
   PETER Engle | Mar 26, 2022 10:44am | #9

   "In my zone 4 do walls dry to the interior or exterior?"

   Both ways, depending on season. Moisture tends to move from warm to cold, so moisture drive is to the exterior in winter and to the interior in summer (if the house is air conditioned). Your wall design is relatively vapor-open in both directions, so drying should be good. As mentioned above, it is best practice not to install vinyl wallpaper, mirrors, or other vapor-impermeable materials on the exterior walls.

6. 
   Cleanair | Mar 25, 2022 06:03pm | #8

   Walter I did purchase and have been dehumidifying while the plasterers were working. The house has been a nice 50-55% since the plaster went up.

7. 
   Cleanair | Mar 26, 2022 11:03am | #10

   Siding has not been installed on the house yet. Should I try to get the builder to install a layer of mineral based exterior insulation such as Rockwool makes?

   Or would using a rain screen over the zip board and behind the siding minimize drying to the interior.

   Thanks