sealed, insulated crawlspace…wrap the piers too?
I am (hopefully) in the final stages of specifying all the details for my new house build in Zone 4A, central NC. I am now in the process of talking to companies who offer crawlspace sealing and insulation and am encountering two different schools of thought with regard to the moisture barrier plastic and how far up the walls and piers to bring it.
It seems to me that an unwrapped masonry foundation pier would act like a moisture wick bringing up the soil moisture and allowing it to escape through the blocks. For this reason I planned to have the crew install a capillary break on the top of every pier and use that to seal the plastic to so that the pier was 100% separated from the lumber and fully sealed.
I am encountering folks that prefer to only wrap the bottom of the pier and only the below grade portion of the foundation walls telling me that the higher you go, the closer you bring the moisture that does escape to the wood.
Is there a consensus somewhere on best practices for crawlspace sealing that really goes into the details so I can make the right choice? If anyone here has some practical experience that they can share on this it would be greatly appreciated!
Thanks.
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Replies
A capillary break, properly installed, will protect the wood from moisture wicked up by the concrete, making the concernts of the contractor essentially moot. The contractor IS correct though -- if you seal up the concrete, water can rise higher (the so-called "rising damp" issue). That is a real concern, but the capillary break is how you address that concern.
I would wrap the piers and call it good, but I would make sure to use a good capillary break that will be reliable over time. My recommendation is to use a piece of 1/32" to 1/16" thick HDPE (High Density PolyEthylene) as a capillary break here, as this material is very durable and long term stable.
Bill
BrunoF,
Just as with stem-walls, the place for a capillary break is between the footing and piers. That will stop any moisture migrating up into the crawlspace.
https://www.greenbuildingadvisor.com/article/adding-a-capillary-break-to-the-footing
https://www.greenbuildingadvisor.com/article/capillary-breaks-above-footings
https://www.greenbuildingadvisor.com/article/capillary-break-at-the-footing
Those are interesting. How would it work if the area between the footing and the cmu are below grade? Seems like water / moisture would come in from the side, above the liquid capillary break and still move up the wall…
BrunoF,
The top of footings are typically close to the bottom of your crawlspace or basement slab. Another capillary break which should be included is a layer of free draining fill directly under the slab, so there should be no water above the capillary break under your piers.
Malcom, thank you! In my case I will not have a slab in the crawl space, just dirt. The backfill / grade on the exterior wall will likely cover up two rows of CMU (min), so I am still struggling to see how the water / moisture from the exterior won't travel along the top of the liquid applied barrier. However, for piers with the footing at or near the the crawlspace grade, I can see a benefit.