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Crawl Space

gws | Posted in Energy Efficiency and Durability on

We’re in the beginning stages of renovating and adding a second floor to a 1,200sf waterfront camp (zone 6A) that will become a “pretty good house”, better than code and air tight as possible. The current crawl space is about 30″ – 36″ high and has a layer of 6mil poly with a thin layer of clean sand for ballast/protection and 8″ CMU foundation and sump pump. There is evidence of water about 3″ up the wall where the ground slopes (half the crawl space) which I’m told by locals happens when the lake floods on very rare occasions. The crawl space appears clean and dry (late August inspection). The finished house will now include ac and heat. The problem is the current owners live out west and will only use this place for one month every July. Therefore the place will most likely be shut down the rest of the time. We may need to use the crawl space for air handlers and duct work (not designed yet). Code compliant venting or non-venting won’t really work with the current owners since they won’t be using the house much and not at all in winter.
What to do about insulating the crawl space?????

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  1. GBA Editor
    Martin Holladay | | #1

    If the lake floods regularly and water enters the crawl space -- even if the water only rises 3 inches in the lowest section of the crawl space -- that's not a good place to install air handlers. Clearly, the air handlers have to go in a mechanical room upstairs. If the homeowners don't want to lose the required indoor area, then build a small addition to hold your mechanical equipment.

    If the crawl space floor is sloped, and there is evidence that the only place that ever gets flooded is the lowest section of the crawl space floor, you can always bring in some fill to raise the floor level of the crawl space in the lowest area. Of course, you lose head room -- but you may avoid standing water in the future.

  2. wjrobinson | | #2

    I renovated a similar camp to year round and we put a boiler in a first floor area after laying cement board on the floor. Radiant floor heat so no ducts in the crawlspace. Wall AC, you could use a split air. The Camps I work on now are set to 45 degrees winters and 80 degrees AC summers just to keep all in a temperate range. Automated dehumidifiers that are self draining.

  3. Expert Member
    Michael Maines | | #3

    A camp with A/C? Doesn't that kind of defeat the purpose of going to camp?

  4. gws | | #4

    Yes a "camp" w/ ac !@@# Go figure. But they're the client and I did try to discourage this but to them it's their summer camp but to future owners it could easily be a spectacular year round home. Hence my for now or for long term.

  5. dickrussell | | #5

    Gerry, does the occasional rise in water level result in wetting of that sand layer over the 6 mil poly sheet? If so, that sand layer becomes a water reservoir and, with the poly under it, will make for a very damp crawl space for some time after those incidents. Then Martin's suggestion to add fill to avoid standing water in the crawl should be heeded. After that, you might consider replacing the sand with a rat slab, with an insulation layer (foam) under the poly, and with insulation on the walls of the crawl, to make the crawl space conditioned, with connection to the rest of the house, to avoid moisture issues down there.

  6. gws | | #6

    Dick, there is no evidence of mold or mildew and the water definitely would flood the poly. Therefore I believe it is a very rare occurrence. My biggest concern is if the house is shut down for 11 months of the year then there is no air movement. To condition the space means leaving the systems running for 11 month when one is there. I'm inclined to use baseboard electric for the current owners and a mini split for ac in the bedrooms and let future owners deal with a proper heating system if they purchase with year round use in mind. We will be insulating to IECC2009
    so now is the time to do it correctly but the current owners won't need it. Opinions welcome?

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