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Community and Q&A

What to do with my crawl space?

tom_h | Posted in Energy Efficiency and Durability on

Hi all,
I’m hoping someone can offer me some good advice on what to do with my crawlspace. I’ve been reading other posts and couldn’t find anything similar to my situation.

I live in Seattle zone 4c and have a vented crawlspace. I have my water pipes and heat ducting (mostly insulated flex duct) down there. It has a plastic vapor barrier in pretty bad shape. The thing that makes mine different is that my chimney runs through the center of my house. If I look up from the crawlspace along the chimney I can see the roof of my house. I want to say that the space from the back of the chimney to the next wall is about 2 feet. So in essence my attic and crawl space are connected.

Currently there is no insulation in the crawl space. I want to insulate it and am looking for recommendations.

I’ve read the pros and cons of sealing up the crawl space but I don’t know if I can do this with the chimney in the center. Do I need this air for the chimney? Can I seal both the crawlspace AND the attic hole where the chimney is located? I’ve read that a sealed crawl space is not needed the Pacific Northwest but since my ducting and pipes are down there am I correct in assuming that a sealed space is preferred?

Any help on what to do, type of insulation…will be greatly appreciated.


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  1. GBA Editor
    Martin Holladay | | #1

    Before you decide whether or not you prefer a vented unconditioned crawl space or a sealed conditioned crawl space, you have to do some basic air sealing work.

    It sounds like your chimney chase is totally unsealed from the crawl space to the attic. While this type of defect isn't too unusual for an older house, it is imperative that you fix the defect.

    The open chase should be sealed in your crawl space as well as your attic. The usual materials to use to seal the air leakage are sheet metal (galvanized steel or heavy aluminum) and high-temperature silicone caulk.

    For more information on this work, see Air Sealing an Attic and
    Air-Sealing a Basement.

  2. tom_h | | #2

    Thanks Martin.
    This is precisely what I needed know! And you are correct that the chase is “totally unsealed from the crawlspace to the attic.” So now that I know I need to seal it up I have attached some pics so I can ask more questions. As you can see the space is pretty big. I am wondering if I need to cover the insulation that I have in there. The distance between the back of the chimney and the facing of the insulation is 14 inches. Can I just seal up the space as you see it in the picture or do I need to do anything else. I do plan on putting insulation on the un-insulated walls. The chimney is hardly used. We light maybe 10 short fires a year.


  3. GBA Editor
    Martin Holladay | | #3

    Q. "I am wondering if I need to cover the insulation that I have in there."

    A. It's a little odd that someone installed kraft-faced fiberglass batts with the paper facing aimed at the chimney. That's not ideal. But as long as the batts aren't flopping over, I think everything will be OK.

    You need to seal the air gap at the crawl space ceiling with pieces of sheet metal, and you need to seal the seams of the sheet metal with high-temperature silicone caulk. Then you need to go to the attic floor and do the same thing.

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