Replies

1. GBA Editor
   Martin Holladay | Dec 19, 2017 01:24pm | #1

   Scott,
   Your reference to "encapsulation" had me confused for a while -- I thought this was a lead paint abatement job -- until I guessed that you are talking about sealing the vents in a crawl space.

   If you plan to seal the vents in your crawl space, you will be insulating the crawl space walls. North Carolina is split between Climate Zone 3 and Zone 4. Most codes require crawl space walls in Zone 3 to have at least R-5 insulation; Zone 4 crawl space walls need at least R-10 insulation.

   If you insulate your crawl space walls, you won't need any insulation in the crawl space ceiling, so there will be no need to install R-30 insulation anywhere. If your building inspector doesn't understand these basic principles, see if you can talk to a supervisor.

   More information here: Building an Unvented Crawl Space.

2. 
   SW514 | Dec 19, 2017 03:29pm | #2

   Hi Martin,

   Thanks for the advice. Your article is one of the ones I found and have been using to plan a lot of the work! :)

   I had a few additional questions come to mind after reading your response and reading your article again:

   1. Do you have any thoughts on a closed but unconditioned crawl space as planned? Is a conditioned crawl space with HVAC providing some air and a vent between the floor a better idea? I was planning a closed space with no HVAC air being introduced, and a radon system + dehumidifier instead.

   2. Should the band/rim joist be insulated as well? I'm wondering if a lot of heat tranfer will happen here if left uninsulated, but also wondering if that area needs to be left open and accessible for termite inspections. I haven't had much luck finding good instructions on how to insulate this portion of the walls other than generally filling in with cut pieces of rigid foam and then using expanding foam insulation to fill gaps.

   3. Will using adhesive to attach the foam board over the walls + liner be okay?

   4. Do I need to use any tape or foam to seal the gaps between boards?

   Thanks again for all the advice. About to order materials and start work over the holidays!

3. GBA Editor
   Martin Holladay | Dec 19, 2017 03:42pm | #3

   Scott,
   It's hard to evaluate your plan. For example, you plan to install a radon mitigation system. That raises several questions: Have you tested your house for radon? Are you a certified radon mitigation contractor? If not, did you consult a certified radon mitigation contractor to make sure that the system you plan to install makes sense?

   In general, rim joists should always be insulated, unless regulations in your area of the country require you to leave rim joists uninsulated due to termite concerns. If you are unsure of local practice, contact your local building department for advice.

   I don't know what you mean by "boards" -- is that the same as rigid foam? If you want to try to adhere rigid foam to a concrete wall, (a) the concrete wall needs to be smooth and dry, (b) you have to use a foam-compatible adhesive, and (c) you have to come up with a way to apply even pressure to the rigid foam for several hours as the adhesive sets.

   One way to apply pressure is to use scraps of plywood or OSB, held in place by long 2x4s or 2x6s that span the width of the crawl space and are wedged in place against the opposite wall.

4. 
   SW514 | Dec 19, 2017 04:02pm | #4

   I realized I should add that I believe the furnace/AC is in the crawl space. So not sure if a vent is needed between the house and crawl space, or if enough return air is coming through the normal ductwork that I will not need to add HVAC aid and a return vent.

5. 
   SW514 | Dec 19, 2017 04:16pm | #5

   Thanks Martin.

   I have tested the house for radon, and it isn't a concern currently with the vented crawl space. The reason I considered at least setting up the appropriate ductwork between the ground and vapor barrier so that I can just connect it to a fan later if needed to address any radon, moisture, or odors and smells that pop up after encapsulation. I will be sure to reach out to a radon professional for more feedback.

   Thank you for the advice on the rim joists, will be sure to follow up with the inspectors.

   For the foam board on the walls, should it go directly against concrete, or if I have vinyl liner from the encapsulation up most of the wall, can it go directly on top of that?

6. GBA Editor
   Martin Holladay | Dec 20, 2017 06:01am | #6

   Scott,
   Q. "Not sure if a vent is needed between the house and crawl space, or if enough return air is coming through the normal ductwork that I will not need to add HVAC aid and a return vent."

   A. I urge you once again to read the article I linked to (Building an Unvented Crawl Space). The article explains that the building code gives you two options for conditioning your crawl space. You can either provide a supply register from your forced-air heating and cooling system, or you can install an exhaust fan in your rim joist. No matter which of these options you choose, you'll need to install a grille in the floor above the crawl space. Details are in the article.

7. GBA Editor
   Martin Holladay | Dec 20, 2017 06:02am | #7

   Scott,
   Q. "For the foam board on the walls, should it go directly against concrete, or if I have vinyl liner from the encapsulation up most of the wall, can it go directly on top of that?"

   A. If you are planning on using adhesive to fasten the rigid foam to the concrete, you don't want to have a vinyl liner on the concrete. (Most types of rigid foam are already vapor retarders, so vinyl on the wall is unnecessary.)

8. 
   Stockwell | Dec 21, 2017 11:47am | #8

   "The article explains that the building code gives you two options for conditioning your crawl space. You can either provide a supply register from your forced-air heating and cooling system, or you can install an exhaust fan in your rim joist. No matter which of these options you choose, you'll need to install a grille in the floor above the crawl space."

   In North Carolina, this is not the case. It is acceptable to have only a dehumidifier in the crawl space and no conditioned air or exhaust fan, thus no grille in the floor above.