Crawlspace in Southern California
I am remodeling a home in southern California. It is a historic home with flat roofs and a vented crawlspace. New AC ducts and ducted minisplit airhandlers are going in the crawlspace. Despite being nearly a century old, the crawlspace is clean and without evidence of water. We are planning on putting a vapor barrier down on the crawlspace dirt. My question is whether in my climate zone (zip 92870) it viable to leave the crawlspace unsealed vs sealed. There is currently no insulation in the house so the decision to seal or not seal will dictate where the insulation goes. I have a wonderful AC/insulation consultant. He is ok with either way and is leaving the decision up to me. I’m looking for a tiebreaker. Thank you in advance!
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Matt,
In your climate, either way will work. If you want a vented crawlspace, it's a good idea to install insulation in the crawlspace ceiling (between the floor joists, or as a continuous layer of insulation directly under the floor joists).
Like Martin said, either way will work. You aren't going to need much insulation either way. In Marine zone 3, you need R5 of continuous insulation on the walls, but R19 in the floor. Even though crawlspace rated foam (Thermax) is more expensive, there is a lot less of it. Doing the walls is probably cheaper, and it brings the ductwork into the conditioned space.
You want ducts in conditioned space.
+1 on making it a conditioned crawlspace. Even if the walls in the house aren't insulated it's still worth insulating the crawlspace walls, since the ducts & air handler are the hottest thing in the house during the heating season, and the coldest thing in the house during the cooling season.
Using 3/4" fire rated Dow Thermax on the crawlspace walls is probably the cheapest way to go. Make sure the cut bottom edge is on the crawlspace side of the vapor barrier, not resting on dirt.
Hi Matt -
I think a continuous air control layer in your crawlspace is essential, even in your mild and forgiving climate. And achieving that continuity at the crawlspace perimeter walls is, in my book, way easier than at the first floor plane of the crawlspace.
So, while I agree either way works, I would give conditioned unvented crawlspace the edge.
While you are in the crawl space and changing the temperature & humidity dynamics - spray Timbor Termite treatment or other termite treatment on any wood that will be covered with foam.