location of dimpleboard drainage outside crawlspace stemwall
Conditioned crawlspace: I’m putting R15 outside my stemwall. On the uphill side it makes sense to have a drainage board since it’s rainy Oregon. [Downhill, the stemwall is open to the air and I’ll cover with hardie panel as a protection surface.]
The layers from inside to out are
-possible plastic liner for crawlspace
-8 inch concrete stemwall
-asphalt damp-proofing
-dimpleboard located either here**
-4 inches R15 insulation (Rockwool comfort board 80)
-or dimpleboard here**
-backfill
My building official said the dimple board should go outside the rockwool insulation.
Rockwool’s technical person said it would go against the concrete.
I imagine both would be ok, but what are your thoughts?
Thank you!
Paula
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Also - any thoughts about moisture getting trapped in the wall if I'm using dimple board, asphalt damp-proofing, and also the crawlspace liner (possibly)? Could there be too many moisture impermeable membranes?
HI PAULA:
You're sure keeping the rain out of your Oregon house. But you could be onto something when you say moisture may stick inside your wall. Without an escape route, water droplets will wreak havoc on sensitive materials. Trapped moisture coated the window frames in my friend's trailer after his dad sealed the windows with ceran wrap. A fix for winter drafts caused moisture condensation between the impermeable plastic and glazing layers . The section remains wet for days after each rainstorm and suffers resulting wood rot. These crevices make a fine nest for leetle cockroaches. Be careful when sandwiching dry things between vapor barriers!
Look into the Comfortboard acting as a drainage layer - potentially eliminating the dimple board.
Make sure that you have a plan for the water once it drains to the bottom of the wall.
Paula, The plastic liner should just run up the walls a few inches - far enough to fasten and seal it to the wall. If you include a capillary break between the footing and the wall, then the plastic liner only has to be sealed to the capillary break and not run up the wall at all. Since you're insulating the stem wall on the outside, you are bringing it into the inside of the moisture envelope, and you want to allow it to dry to the inside.
As Jon says, the Comfortboard can act as a drainage layer in many applications. If you want the added security of the dimple board, you should follow the Comfortboard manufacturer's guidelines. Most code officials will accept manufacturer's installation instructions as guidance. In practice, it probably doesn't make any difference where it goes. Make sure to terminate the top of the dimple board with a termination bar so that soil and water cannot get between the dimple board and the wall.
Thanks to all of you for your responses. Peter, I like your suggestion for not coming all the way up the wall for the crawlspace liner. Any moisture that did get into the walls could migrate into the crawlspace air and be conditioned along with the home interior air.
Yes, I do have a perforated drain at the bottom of the footings.
Can anyone else weigh in on using the comfortboard 80 as a drainage layer (and skipping the dimpleboard)?
Mineral wool boards are physically unaffected by wetting, but I wonder if it de-rates the R-value? Anyone know?