Replies

1. GBA Editor
   Martin Holladay | Aug 02, 2018 04:44am | #1

   M.H.,
   It looks like you tried to cram all of your question into the title box, and the question was truncated. I tried to salvage as much of your question as possible, but it is obviously incomplete. Maybe you'll add the missing information and question as a comment on this page.

2. 
   Pearlconstruction | Aug 02, 2018 06:52pm | #2

   Thanks, and I’m sorry. I posted from my phone and didn’t realize what I did.

   So we furred all the exterior walls out for MEP. We encapsulated the house and have a hot roof. We used 2 lb foam.

   We started noticing moisture related issues recently. We have mildew/mold in some base cabinets and in some closets.

   My ground source system does not have to work very hard so we battle high humidity in the home.

   I think I know what the problem is, but would like to see your thoughts.

   The foam on the bottom side of the floor system is only an avg. of 1”. I think I am getting moisture coming up through the floor and getting trapped in the house. We have 3” on the walls and 4” on the roof deck.

3. Expert Member
   Peter Engle | Aug 02, 2018 09:11pm | #3

   I don't think your problem is the 1' foam. I think it's the brick walls and internal moisture sources (cooking, cleaning, bathing, breathing, etc.)

   With foam on all sides, you've built yourself a foam cooler. Anything inside stays inside. The brick walls are still in contact with the soil, and probably are wicking a lot of moisture up from the ground and emitting it to the interior. Without adequate air exchange and/or dehumidification, it just builds up. In summer, air exchange won't actually help much because it's humid outside, and that humid air won't dry the house. As you have noticed, the insulation means that your A/C system doesn't run much, so it doesn't have a chance to reduce humidity. Chances are, it's oversized as well, reducing moisture removal even further.

   You should have a long talk with your mechanical contractors to figure out the best way to dehumidify the house. there are many options, considering some of the hints you've dropped about your equipment. If you don't have any dedicated air exchange equipment, you should install some, even if only for IAQ reasons. That might not help with the humidity much, but it is still important. Your ground source system may be able to be jiggered to provide a dehumidification mode, and that would be the most efficient way to do it, but might mean some expensive alterations.

4. GBA Editor
   Martin Holladay | Aug 03, 2018 05:31am | #4

   M.H.,
   We need some more information.

   1. I have no idea what "MEP" stands for. Can you explain?

   2. When you said "We used 2 lb foam," I assume you mean closed-cell spray polyurethane foam. Is my guess correct?

   3. It's a little unclear whether you installed the spray foam on the interior of the bricks or the exterior, but it sounds like you installed the foam on the exterior. Is that correct? If so, what did you install as cladding on the exterior?

   If you've tightened up your home with spray foam, you have almost undoubtedly reduced the rate of air leakage through the home's thermal envelope. Every tight home needs a mechanical ventilation system, and in your climate zone, it's typically helpful to have an HVAC system capable of addressing high levels of indoor humidity during the summer.

   So, does your house have a mechanical ventilation system? If so, can you describe it?

   Peter is correct: the two most common ways of reducing high indoor humidity during the summer (especially if you live east of the Rocky Mountains, where the outdoor air is often humid) are (a) to operate an air conditioner, or (b) to operate a dehumidifier. Sometimes you need both.

   For more information, see "All About Dehumidifiers."

5. Expert Member
   Michael Maines | Aug 03, 2018 08:15am | #5

   "MEP" stands for mechanical/electrical/plumbing. In other words, M.H. created a service cavity by furring out the walls, most likely to the interior.

   2-lb foam is a common way to describe closed-cell foam, for its weight per cubic foot. (Open cell foam is about 1/2-lb pcf. And there is an in-between option that combines the worst features of open and closed cell...)

6. GBA Editor
   Martin Holladay | Aug 03, 2018 09:24am | #6

   Michael,
   Thanks for the "MEP" explanation -- as soon as I read that, I remembered. (I had been tripped up by the same abbreviation in an earlier Q&A thread.)

   As you can see, I correctly guessed what was meant by "2-pound foam" -- but for the sake of clarity (for the benefit of all GBA readers, and even, occasionally, for the benefit of GBA editors), it's always best to describe materials in an unambiguous, easy-to-understand way.

7. Expert Member
   Michael Maines | Aug 03, 2018 09:38am | #7

   Martin, I agree--our society, and perhaps our trade more than most, has become a sea of acronyms and abbreviations. (Or a SOAA?)