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Crawlspace encapsulation help (take 2)

ChrisInIllinois | Posted in General Questions on

As I continued my reading and tried  to find “pros” with nice tools like an hilti Gx-IE to come to my aid, I have come up empty, left with more questions. I am in 4A climate zone

after spending a great deal of time in my crawlspace that has lose laid plastic some black some white. I am trying to come up with the most cost effective and manageable install.

It seems I will have to have my foam board covered for my application, but this leaves me with an issue. for the cost of the fire retarder / barrier in drywall or cement board, etc.. I could use a contentious layer of mineral wool screwed in to furring strips and get another r8 to r15 on my crawlspace walls. The thing is  
Martin Holladay seems to be against any type of batt insulation in a crawlspace.

If this the mineral wool over foam approach is do able, I could save a huge chunk of money by only using R5 foam. It would help in installing too. horizontal furring strips could be installed with a powder actuated fastener vs hammer drilling. The furring strip + foam board would act as a mechanical fastener keeping the poly and adhesive tape product sealed to the wall. I read a post calling this an hybrid approach. It seemed to work and not matter in my climate about due point and foam thickness.  

Does it matter from a long term point of view if I use powder actuated fastener vs hammer drilling for concrete block? I don’t think drilling in 18″ of crawlspace (before joists around 24″ deep.) will be fun, at the least it will be slow moving lol.

Whats the deal with the poly sheet and the wall? I get an overlap to keep  foam from contacting the ground and to seal the edge for moisture. The thing is I have read so many papers and companies install is the summary:

poly all the way up the wall, then foam.

poly  6 to 12 inches up wall then foam.

Foam then cover it up the wall with the poly.

No poly on the wall the foam is fine by its self.

termite inspection strip, I cant seem to find code on this, but I am not in the very heavy zone.  just moderate to heavy. I don’t see an issues nor did my home inspector before buying. Is it best practice to just leave that 3″ gap?

Water and foundation: 

I have installed gutters. atm they are 6+ feet out, working on underground drain to ditch.

I have fixed any grading issues and the land is sloped away from the house on all sides. I would like to add more fill but that is another topic another time.

I dont see any water  issue in the crawl, but it is below grade a few inches.

Should I paint / add water sealer to the outside of the concrete block?
Am I over looking anything?

Thanks for your time, hopefully I can come up with a finalized plan.

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  1. Expert Member
    BILL WICHERS | | #1

    I’ll leave 1 and 2 to others. I’m a rigid foam guy :-)

    2.2: I don’t like powder actuated fasteners. Too much chance of a blowout, or failure to set the anchor properly. Ricochets are a risk too. You can’t use them with rigid foam due to inability to properly handle the depth. I’m not sure why you’d need to drill 18”. Drill in a few inches and use a push-in insulation anchor such as those made by Hilti. Tapcons can work too, but need fender washers of some type to avoid punching through the foam.

    3: foil or poly faced insulation can work the same as the poly crawl liner. It’s possible to only run the crawl liner up a little bit on the walls and let the insulation do the rest. I like to run the poly crawl liner all the way up the walls and then put the insulation over the liner. I like the way the system goes together that way, and I don’t have to rely on tapes to hold the liner in place. I run the liner up the wall, held with a furring strip near the top. Insulation goes up to the bottom of that furring strip. Spray foam then seals the insulation, liner, and rim joist areas. No leaks this way. Make sure you have a capillary break between the masonry foundation and the wood structure of the house.

    4: if you’re in a termite zone, you need the inspection strip. I’m not in a termite zone, so I’ve never had to deal with this.

    5: you always want water to run away from your house. You don’t want any water to get inside. I’m not sure you really have a question here?


    1. ChrisInIllinois | | #2


      the 18" is my working space, before the floor joists.

      termites gap:
      are you in the in the white on the termite map? or are you just saying you omitted the gap because you are not in the red?

      I am in the blue on the map. based on building codes you need to be in the red for it to be a issue with foam.

      would you mind explaining this "Spray foam then seals the insulation, liner, and rim joist areas." are you saying you over lap the foam board, liner, rim joist with 2 part foam?

      I planed to cut and cobble foam for the rim/sill plate. maybe spring for a dow forth pak. depending on the method I had a few ways I was going to seal the top of the foam board and or vapor retarder, but would love your thoughts on how you do it.

      Thanks for the info, time and the reply.

      1. Expert Member
        BILL WICHERS | | #3

        I’m on the edge between the White and yellow areas on that map. No one in my area has ever had any issues with termites.

        Spray foam will seal the rim joist, ends of joists, top of the foundation wall, and any crawlspace liner together.


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