GBA Logo horizontal- lakesideca.info Facebook- lakesideca.info LinkedIn- lakesideca.info Email- lakesideca.info Pinterest- lakesideca.info Twitter- lakesideca.info Instagram- lakesideca.info YouTube Icon- lakesideca.info Navigation Search Icon- lakesideca.info Main Search Icon- lakesideca.info Video Play Icon- lakesideca.info Audio Play Icon- lakesideca.info Headphones Icon- lakesideca.info Plus Icon- lakesideca.info Minus Icon- lakesideca.info Check Icon- lakesideca.info Print Icon- lakesideca.info Picture icon- lakesideca.info Single Arrow Icon- lakesideca.info Double Arrow Icon- lakesideca.info Hamburger Icon- lakesideca.info TV Icon- lakesideca.info Close Icon- lakesideca.info Sorted- lakesideca.info Hamburger/Search Icon- lakesideca.info

Community and Q&A

Is external insulation necessary for moisture control?

Debra | Posted in Energy Efficiency and Durability on

My new home will be in climate zone 4A, in the mountains of Virginia – a mixed humid climate. My budget is somewhat limited. Our house plans have 6″ walls, 24″ on center, with R23 mineral wool batts. Taped plywood sheathing, Tyvek, and vinyl siding on the outside. The main air barrier will be sealed exterior sheathing and the drywall ceiling. The house will be pretty air tight.

I will also be doing 2 additional things:

1) Sealing the top and bottom of the drywall, to reduce interior air penetration and air circulation inside the walls (though not to the point of doing full ADA, since my full air barrier is on the exterior)

2) My goal is to keep our interior humidity levels to no more than 30-35% (not usually a problem in winter if I don’t use a humidifier)

These walls will be able to dry out on both sides, and not much interior air should get inside them. Do you think this wall design will do a decent job of controlling moisture inside it, in my moderate climate?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Debra,
    There shouldn't be any reason for the wall you describe to have moisture problems, as long as you pay attention to flashing at windows, doors, deck ledgers, and other penetrations.

  2. Debra | | #2

    Excellent! Thanks. Yes, I'll be paying great attention to the flashing details.

  3. Andy CD Zone 5 - NW Ohio | | #3

    Debra, a goal of 30-35% RH in a place that is "pretty airtight" may not be as easy to achieve as you expect. Depending on the actual airtightness and the occupants' lifestyle, low wintertime RH will be a thing of the past and it may even be a struggle to get the RH down into the low 30s. In one sense it's a vindication of the energy-saving effort and expense you put into your house's envelope, but high RH might lead to sleepless nights worrying if it might be condensing somewhere you don't want it to. Make sure your HRV or ERV installation is well designed and and professionally installed--don't skimp on this. DAMHIKT.

  4. Debra | | #4

    Yes, I plan to have good mechanical ventilation with the ability to adjust for various rates of cfm airflow.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |