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Community and Q&A

An Idea That Maybe No One Cares About

user-1087436 | Posted in General Questions on

I was just looking at the Home Energy Pros website ( I can’t join, but at least I can look), and I found a short thread about sealing crawl space vapor barriers and insulation to concrete walls. There was some discussion about how to hold the materials in place against the concrete wall while the adhesives (mastic etc.) set (prior to mechanical fastening). One commenter wrote that he didn’t really have a good way. I thought: Why not curtain tension rods? I mean the kind with rubber tips that adjust in length and stay in place by spring tension. They are cheap (about $5 ea.), and they could be set vertically between the ground and the bottom of a floor joist as a means of temporarily supporting, for example, the plastic vapor barrier and the insulating foam board.

Comments? Sneers? Embarrassed Silence?

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  1. GBA Editor
    Martin Holladay | | #1

    When you're adhering rigid foam against the concrete wall of a crawl space, a curtain tension rod that stretches between the dirt floor and the joists above won't help you. However, when I've done this work in the past, I've used 2x4s that are a little longer than the crawl space is wide. For a 20-foot-wide crawl space, you need a 2x4 that is 20'6" long. (Of course, you can screw two 2x4s together if you want.)

    First you put scrap pieces of plywood or OSB over the foam, and then you use the long 2x4s at a slight angle to hold everything in place until the glue dries.

  2. user-1087436 | | #2

    Thanks, Martin. I wasn't sure if my post deserved a reply. But what happens if you're building an 1800 sf house that has one story (because you're getting old and your wife has a debilitating disease, etc) and your walls are 38' on one side and over 50' on another? Placing a 2x4 that long sounds like something for a Laurie and Hardy sketch. I don't see why a few tension rods couldn't help you do the work in sections. Surely they could hold up the foam and a few scraps of plywood. (????)

  3. GBA Editor
    Martin Holladay | | #3

    Give it a try. I suspect they won't provide enough sideways pressure.

  4. homedesign | | #4

    Hi Gordon,
    Kudos to you for building a Not-So-Big House and a ONE Story ...User/Age Friendly House

    One of my favorite Lstiburek Quotes:
    "The Best Crawlspace is NO Crawlspace"
    Have you considered building a slab on grade?

  5. user-1087436 | | #5

    John, I can see why slab on grade has its appeal. However, a crawl space with utilities open and accessible also appeals to me. Plus, the thought of walking around day after day on hard unyielding concrete does not seem like something we want to do. I mean, we'll be in an "institution" soon enough; I don't want to start too soon. Does this seem reasonable?

  6. 5C8rvfuWev | | #6

    Very reasonable, Gordon. I'm planning a similar house (and plan on aging in the place for two people with bad knees and a bad back) and solved the dilemma of the unyielding slab by designing to use sleepers and advantech over the slab, then cork. The plywood doesn't know it's suspended by sleepers instead of joists; and the cork is resilient.

    The utilities are planned for overhead in chases/soffits. That, admittedly, eats up the $$ I will hope to save by using a slab.

  7. homedesign | | #7
  8. user-1087436 | | #8

    Many thanks, John, for that link, and to JoeW for his comments. Another amazingly instructive article from Mr. Lst. But I looked at Figure 1 and thought: That's just a crawl space structure with a bunch of dirt dumped in where the crawl space would be! I'm in zone 4C, by the way, so I guess this is the one he recommends. I'd rather just build a crawl space, the way builders in our area are used to doing, eliminate the vents, add a rat slab (over plastic) to make it a short basement, and then put foam on the walls and in the joist pockets.

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