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Community and Q&A

Connecting two crawl spaces

timmyzaid | Posted in Energy Efficiency and Durability on

I’m in the process of encapsulating and insulating two (currently) separate crawl spaces in my mid-60’s built home. One of the spaces is under part of the original house adjacent to a finished basement, the other is under an addition built sometime later. The two spaces are next to each other with only a small hole for a HVAC duct between them. My question is, should I cut a larger opening between them in order to allow better air circulation once they’re fully encapsulated?

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  1. GBA Editor
    Peter Yost | | #1

    Hi Timmy -

    1. I am assuming that when you say "encapsulating and insulating" the two crawlspaces you mean doing this on the perimeter walls and the crawls will be unvented?

    2. what type of wall is there between the two crawls?


  2. timmyzaid | | #2

    1. Yes, that's exactly what I'm planning to do. Originally both were insulated between the floor joists but that ended up creating a mess.

    2. There is a cinder block wall with bricks on one side of the face, originally an outside wall of the house.


  3. Jon R | | #3

    > I’m in the process of encapsulating and insulating

    Better to say "encapsulating, insulating and conditioning". A hole between them is likely to be useful wrt the last one.

  4. Zeker234 | | #4

    I have a similar issue with two crawl spaces. I’m having it professionally encapsulated with a dehumidifier in the bigger space. How big a hole from the smaller space is needed for the dehumidifier to work in the smaller space?

  5. plumb_bob | | #5

    I think the answer will always have include "it depends on..."

    If you have 2 crawl spaces with significantly different construction, insulation, air and vapour barriers, ventillation etc. it will be a difficult building science thought process to join the 2 effectively. I know because I have an old house with a terrible old crawl that I want to build an addition onto, and the way to connect the 2 crawls has been occupying my brain for some time. I think I will end up keeping the 2 separate, one modern and fully connected to the house, and one old school that is semi-conditioned but seems to work. During construction of the addition I will add some hrv supply and return runs to the old crawl to help with ventilation.

    1. Zeker234 | | #6

      So both my spaces are going to be professionally sealed. I’m asking how much air flow do I need between the two spaces. I’m going to have a top notch professional dehumidifier specifically sized for my space. I want to get some air flow from smaller space. Cinderblock wall that I’d have to have opened up or I can cut holes in the rim joist.

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