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Do I need a concrete floor in my crawlspace?

user-967937 | Posted in Energy Efficiency and Durability on

Hello GBA

I’m in the process of planning a new home for my wife and I in the Pacific Northwest (4C climate zone), is there any reason besides durability to pour a concrete floor in the crawlspace?
This will be a conditioned space, foundation will be ICF’s with all the waterproofing details intact, just seems like a lot of $$ and energy to pour a slab that will see little use. I may be down there twice a year to change the filters in a couple of pieces of equipment, but it won’t be used for storage or much else.

My thoughts were to lay down a layer of 2” XPS with 20 mil on top sealed to the walls….only obstacle I can think of may be the requirement of a fire barrier?

Thanks in advance!


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  1. GBA Editor
    Martin Holladay | | #1

    Check with your local code official concerning you plan. It's possible that your local code will require a thermal barrier over the rigid foam.

    Assuming that you get the OK from your code official -- no, you don't need a concrete slab if you aren't planning to use the area for storage.

  2. user-723121 | | #2

    I like a slab in a crawlspace, it is really nice if you need to do some wiring or the like later on. Does not have to be 4" concrete, 3" is ok. You will get a bit of thermal storage with the slab as well.

  3. user-659915 | | #3

    I'd go with best local practices - talk to local building officials and experienced contractors. In my area crawl space concrete is very uncommon, with no apparent ill effects, but in other regions there may be very good reasons for a 'rat slab'.

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