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I've seen conflicting info on this. Some sources say that you shouldn't insulate your foundation wall because moisture can get trapped between the insulation and the wall. Others say that the insulation is a key part of the encapsulation.

I'm assuming that the answer to which is right is: "it depends." So my question is, what does it depend on?

I'm assuming that some of the factors that matter are:

  • Is the sill plate sealed?
  • Will there be a dehumidifier?
  • Will the HVAC system be serving the crawl space at all?

What else matters?

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  • what is your climate zone? these are specifically foundation walls in a crawl space? crawl space is unvented? generally in a primarily heating climate you want to prevent moist warm air from reaching cold surfaces where it would condense.
    – Fresh Codemonger
    Mar 18, 2021 at 20:13
  • This is Atlanta, hot humid summers. Yes, crawl space specifically. Venting is TBD. I had thought the whole point of encapsulation was to eliminate vents, but apparently that's not true.
    – brentonstrine
    Mar 18, 2021 at 20:35
  • You don't want to vent a crawlspace in a humid environment, like Atlanta. During much of the time, the warm, moist air (80 deg, 80% relative humidity, or RH) will enter the crawlspace, the RH will increase because of the drop in temperature in the crawlspace. When it reaches the dew point inside your crawlspace, it will condense on any and every surface in your crawlspace.
    – SteveSh
    Mar 18, 2021 at 22:07
  • @SteveSh yes, that is exactly what happened resulting in tons of mold which I am (expensively) having removed now. So I am shocked that code seems to forbid closing off vents and dehumidifying, hence that other question I linked to.
    – brentonstrine
    Mar 18, 2021 at 22:10
  • The Mid Atlantic, where I live, is only a little bit better than Atlanta. I keep my crawlspace vents closed up most of the time during the summer, and only open them when the dew point temperature is lower than the temperature in the crawlspace, somewhere around 50 deg or 55 deg. I also run a dehumidifier in the crawlspace, and the dirt floor is covered with 6 mil poly.
    – SteveSh
    Mar 18, 2021 at 22:10

3 Answers 3

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I think the accepted best practice is now to make crawl spaces part of your conditioned living area. Insulate and allow air to circulate like you do in the rest of the house. The best practice for new builds may not work depending on your construction details. You should check out how Risinger Homes out of Austin Texas handles it.

https://www.youtube.com/watch?v=5n4K170f56I

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The answer is no, as the crawl space is not a living space, the moisture changes have no detrimental effect on the foundation material; unless the chemical contents in the air/water are too high, or the space is enclosed and utilized as utility room. Also note, installed over wet/moist surface, the insulation may cause more headaches (mold, hidden cracks), and wouldn't stay long anyway. You may consider apply waterproof on areas that in direct contact with soil, to protect the foundation from surface water runoff.

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    It's not a hard no. In one personal case the walls were insulated to help prevent pipe freeze in winter. Vents were closed and an HVAC duct was opened to partially heat the space.
    – isherwood
    Mar 18, 2021 at 21:17
  • In wall piping in cold region?
    – r13
    Mar 18, 2021 at 21:28
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    Nope. In the floor (or under it). Got to get from one room to another somehow. :)
    – isherwood
    Mar 18, 2021 at 21:37
  • I think the OP is talking about foundation wall (vertical plane). No doubt the bottom of floor shall be insulated. Pipe runs in wall posses huge assess/repair problem, as it is not too difficult, nor expansive to insulate exposed pipe, so it is advisable to avoid embed pipes in the wall. This is just my opinion though.
    – r13
    Mar 18, 2021 at 21:53
  • @isherwood I think I got your message. Please see the updated response. Thanks for your comment that leads me to think deeper.
    – r13
    Mar 18, 2021 at 22:09
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This is what I did. Covered the floor with 6mm plastic from Home Depot and spray foamed the walls. Added a dehumidifier that will pump out water through the vent. enter image description here

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