Crawlspace encasement
Hello,
Here are the details for what an insulation contractor completed as part of an overall crawlspace encasement below a small first floor heated space. Question follows:
Plastic (black) covering the dirt floor.
Plastic comes above the sill plate and then is sealed with foam where it meets the Tyvek covering the exterior wall studs that have fiberglass bats.
It’s probably 1-1.5 feet from the dirt to the sill plate (dirt, cinderblock/stone, sill).
Exterior is stucco.
House is mid 1920s, and the wood is circa about that time (i.e., super solid).
Climate: Northern Illinois
Is there danger of rot or mold developing on the sill plate and/or where the studs meet the sill plate? I ask because in winter when it is very cold, a large air bubble develops under the plastic. This made me think some type of temperature variance may be causing condensation, etc. With the plastic being black, I can’t inspect. The contractor that did this, an insulation company, is generally pretty reputable to my knowledge, attends building science seminars to stay up to speed, etc., so I really didn’t question it… until recently for some reason.
I had a thought this spring to cut the plastic at the seal point and have it lay flat on the dirt (i.e., cover ground for vapor barrier without encasing). I confess to being a little scared of what I might find. I’d be okay with not as tight an encasement so as to avoid mold or rot (if it’s not too late already).
Thoughts? Opinions?
Thanks!
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Replies
Perhaps there is air leakage under the sill. As the stack effect of air leakage from the ceiling above depressurizes the space, air coming in under the sill causes the bubble. Worse in winter because of the temperature differential.
If you have access to the exterior of the sill, applying a bead of sealant at the sill/foundation juncture may stop the air leakage.
You can cut the plastic to inspect underneath, then tape it back together with tape made for the purpose (americover stocks such tape as do other places).
If you decide to replace that plastic one day, I’d use white. White makes the space much brighter and nicer in my opinion. You don’t see clear very often (I’ve never seen it) used in this application.
Bill
Your title tells me you are thinking about this is the wrong way.
You can vent the crawl space or condition it, you are asking for trouble if you try to be somewhere in between and call it encapsulated or encased.
If you want to condition it you need to insulate the walls and supply enough warm air to the crawlspace to keep the walls above the dew point.
Walt