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Monolithic slab with foam and rain – floating problem?

mikeysp | Posted in General Questions on

Hi, I am in Zone 4a (Nashville area) and it is a VERY rainy area. 

I within weeks of forming and pouring a monolithic slab. Since I am a DIY builder, it is a SLOW process. 

I will be digging into the pad I have formed for the edge beam. Once the 4″ gravel base is in, it will be covered with 3″ of recycled 25psi XPS that I acquired.  2″ of foam will wrap under the footer/beam and run up the exterior. 

I am concerned about rain water ponding in the footer and lifting the foam up from buoyancy. 

What solution is used to prevent this besides pouring right away as I cannot operate that fast. 

I thought I might trench out at footer/beam depth so the footer/beam hole acts as a rain gutter. 

Thank you.


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  1. this_page_left_blank | | #1

    It seems to me that your foundation base should be such that water drains away. If there's enough standing water around and under the foam to float it up, that's going to be a problem even after the slab is poured.

    1. mikeysp | | #2

      Trevor, my thought was that I would use my backhoe bucket to dig the footer and the earth would be my footer form. After my slab is in place, I was going to dig along the edge and install a gravel and slotted pipe french drain. I do not know how I would install it before the slab is poured.

      Please correct me if I am off azimuth.

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