Finding the frost-line under a slab?

ladybug-tools
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Hi! This is a bit more of a ‘building-physics’ question than software-related, but I wonder if maybe anyone has any suggestions on the right approach to answer this question:

Question:

Given a slab-on-grade foundation in a known climate (New York, USA), and with a proposed insulation detail, what would the suggested method be to determine the location of the frost-line under the building, and specifically to assess the proposed detail for risk of frost-heave damage?

Screenshot 2025-03-25 at 4.56.27 PM
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What I Considered:

I initially looked at this detail using a 2D heat-flow simulation following the ISO-10211 protocol for footings, but I am thinking that this static analysis method is not really appropriate for capturing the real performance of the soil, given its heat storage capacity?

I know that tools like Kiva can also be used to model soil temperature in EnergyPlus simulations, but that also doesn’t sound quite like the right tool for this question either?

So: does anyone have a suggestion for a methodology or software setup to assess a question like this? Has anyone every tried to model something like this before? Any thoughts or suggestions are much appreciated as always!

best,
@edpmay

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hey @edpmay,

Kiva seem to be a right tool for the job as it is a transient coupled ground-foundation model, which can output temperature fields. I think as long as you check the limitations and the foundation design is captured within the presents, it should be fine.

I have dealt with this problem, but it required detailed thermal bridging simulation and some more advanced physics, as well as 3D outputs, so I used conjugate heat transfer solver in OpenFOAM. Essentially, you need a transient conduction solver and a proper climate data to assign as a boundary condition of the ground. As you pointed out, thermal mass of the ground plays a critical role here, so you need to run a simulation for ~5 years for stable conditions.

For risk mitigation you may need to consult a structural engineer on the frost-heave action, and try different options on insulation and deepening of the foundation.

Cheers,
Dmitry

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