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I’d like to build a sauna on my property. Building footprint 12′ x 16′. Northern Minnesota location. High ground location, well drained (sand/gravel) soil. Floating slab or full perimeter frost footing? Local opinion varies. What do you think?
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Wayne - from over here in northern WI I'd say floating slab. Course my house and sauna are both on slabs, so I have a preference. Footings to below frost line are vastly overrated in my opinion (they work fine but a slab is so much cheaper and if done right works just as well). If you are concerned about movement (and if your soil is well drained, as you say it is, I wouldn't be) consider an inch or two of extruded styro board under the slab and maybe 3-4 feet out around the periphery. Backfill over it and you should have no problem with frost under it. That's how my house is done and on very poorly drained clay.
*Wayne- I am in southern Alaska and I agree that below frost-line footings are overrated like Royboy said. You must be looking at frost levels of 6' to 8' like up here...and it seems silly to do that kind of excavation for a 12x16 outbuilding.I have a remote-site cabin without running water and used treated wood posts and pads for my foundation and am planning on doing the same for my sauna.Consider a girder size to span 16' and then you only have to dig 4 holes since sizing joists to span 12' is no problem. Without any posts down the middle you don't have to worry about crowning your floor when those outside posts settle a bit. Good luck.
*As Matt says, pole or post construction is another cost-effective foundation option (other than house and sauna my other outbuildings are pole-framed). Probably depends on what sort of floor you want in sauna. I decided a slab with a floor drain to daylight best served me in a sauna and that led to the floating slab (though the attached dressing room is wood floored with posts on floating pads). If you want a wood floor, go with posts/poles or do removable "duckboards" on top of a slab.
*Wayne, Had an uncle up by Chisholm that located his sauna over/near a spring. Small depression in the concrete floor for a spring fed pool kept the beer cold. Nice touch.