Wing insulation in regards to depth

[sveink]

Hello
I'm designing sole foundations for a heated building where the anticipated frost depth is only marginally above the foundation depth. Foundation depth is 900 mm and frost depth is 800 mm.

I'm wondering if there's need for wing insulation (both considering frost heaving and heat transfer), and more than that if there's any documentation of the correlation between foundation depth and dimensions of wing insulation.

If anyone can help, thanks in advance!

 

[CarlB]

I'd say no need for wing insulation.

Practical examples I know of, the standard design practice in Anchorage and Fairbanks, Alaska is to provide only 2" board insulation on the foundation wall, no wing insulattion. Design depth to bottom of footing is 42 inches. Design frost depth is 10 feet in Anchorage and over 12 feet in Fairbanks.

The insulation helps direct building heatdown below footings, maintaining the ground continuously thawwed underbuildings.

If less than 42" depth of footing is provided (which is allowed), then wing insulation is used.

Search for "frost protected shallow foundations" for design guides.