Hello Everyone, I am building a Yurt in Idaho mountains at ~ 6,000ft above sea level. The build so far is as follows: 2 feet of compacted stone; 15 mil virgin vapor barrier; 35'x35' of a 4" Concrete slab, fiber & Rebar; On top of the 4" slab I built the Yurt "foundation": 34' diameter x 6" wide x 6" tall stem wall (this is what the yurt sits on). My question is what is a decent way to fill the 33.6' diameter x 6" deep ring? My plan is: use 4" XPS R-20 rigid foam around perimeter (the stem wall); use 4" XPS R-20 rigid foam around the first 4' on the slab (the floor); use 2" XPS R-10 rigid foam for the rest of the floor Have the hydronic tubes about 1" below the surface with a concrete fill. Also, the walls of the yurt are 40mil vinyl, with R5 insulation and same for the roof. Note: I have a Vermont casting defiant wood burning stove in there as well. Does the very low R-value of the walls and roof impact the radiant floor design?

Use EPS instead of XPS for the insulation. Over time EPS will have the same R-value as XPS and is much greener for the planet. This is a green building site after all.

If you are asking how to fill the interior foundation cavity, you could use self-compacting pea gravel.

Yes, the first step in properly designing a hydronic radiant floor system is knowing all the construction assembly R-values so you can accomplish a proper heat loss analysis using your local 99% outside design temp. Once you know your heat loss, you can design the PEX circuit spacing, circuit lengths, circuit flow rates, resulting circuit heads, the pumping size requirement, supply/return temps and select appropriate heat source, etc. There are some free DIY heat loss and hydronic radiant design software on our website that should work well for this simple project:

https://www.borstengineeringconstruction.com/Heat_Loss_Analysis_Calculator.html

https://www.borstengineeringconstruction.com/Hydronic_Radiant_Floor_Heating_Design_Calculator.html

Good luck with your project!

EPS should cost less than XPS and be greener. Ideally, the insulation should be installed in more than one layer so joints can be staggered to avoid thermal bridges.