Horizontal skirt of XPS at footer; useless?
This statement “For the cases examined, horizontal skirt insulation (at the footer) has a negligible impact on the annual sensible heating load” comes from the Conclusion section of a report “Analysis of Basement Insulation Alternatives”, by Ian Beausoleil-Morrison & Briana Paige Kemery, Mechanical & Aerospace Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, ON, Canada K12 5B6. The “skirt” (typically, in Fairbanks, AK) is a two foot wide piece of XPS that is installed horizontally on the outside of the foundation wall, just above the a footer. Adding this horizontal skirt is recommended here in Fairbanks. The intention of adding the foam here, I think, is more to usher the isotherms out farther away from the footer, than to save heat. I’m curious about what people in other cold places think of this, and what options are used.
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I think you hit the nail on the head.
I've been considering this type of foundation as well for my cold climate house (10400 HDD). It seems like a good way to save all the concrete that would otherwise go into a deep frost wall.
If you haven't seen it already here is a design guide (food for thought):
http://www.toolbase.org/pdf/techinv/fpsf_techspec.pdf
Soil conditions may be a consideration in your area:
https://www.greenbuildingadvisor.com/community/forum/general-questions/16210/foundation-options-expansive-clay-soils
Yup. It's not for insulating the basement but for protecting the footings from frost penetration. It's been done haphazardly as footing protection, and it's been done scientifically as part of a frost-protected shallow foundation such as has been used in northern Europe for decades (now accepted by the IRC).
Roger that; maybe I'm learning some stink. I think the Cold Climate Housing Research Center has info on fpsf's, but I've never been interested in reading; too much else to do.