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How to protect a shallow monolithic footer during winter construction, zone 5

lucyna99 | Posted in PassivHaus on

We have a Passive House design, which includes a shallow and 1’4” wide mono footer. 4” floating slab has 12” deep thickened edges. 12” under the slab are insulated. There are 4” of EPS on all 3 sides of the footer. (see detail/picture).

Our builder is concerned with using mono footer due to the winter timing of the job. If we proceed as designed, all utilities and insulation have to be in place before the footer and slab can be poured, and only later the walls are to be erected. How can we protect this shallow concrete footer from adverse effects of cold on the setting concrete? What could be the best practices to use here? Would we have to wait for a long time, loosing time? The assumption is that we push through with the construction through winter.
Per our builder, the traditional footer would have been much better protected by the earth around it. The timing of the pour is also impacted by the sequencing.
If we had the traditional footer, these could be poured first (still before Thanksgiving, which appears to be a “deadline” for such pours in our PA, climate zone 5 area), then maybe utilities, walls, roof erected and only then slab poured. The same cannot be done with the mono footer.
Is the main dilemma related to loosing time waiting for the cure..? We are newbies, so please don’t hesitate to explain trivial areas of builder’s knowledge, please.
The insulation around the mono footer is pretty essential in Passive House design, so we don’t want to give up on it…

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  1. GBA Editor
    Martin Holladay | | #1

    There are two separate issues to worry about:

    1. Keeping the concrete warm until it has cured enough to stop worrying (less than one week).

    2. Making sure that the soil under the foundation doesn't freeze and heave.

    Issue #1 can be handled by placing the concrete during a warm spell of weather or, if necessary, using a tent (like the one shown here: Placing Concrete for a Passivhaus Foundation).

    Issue #2 is a non-issue -- you have enough foam to prevent the soil under the foundation from freezing.

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