What kind of foundation?
I would like some recommendations and pros/cons of various foundation types for my parent’s retirement house which will be built in west-central Idaho (climate: cold/6B). Frost depth is 28″ for construction purposes. My parents don’t really want a basement. I think the two likely candidates for foundation type are slab-on-grade and crawlspace.
I have looked a bit into pricing for the foam SPFS slab forms – they seem pretty pricey. I am considering a T-shaped house with about 1681.75 square feet on the main/ground floor, along with about 439.3 square feet of covered porch/patio space. Legalett pricing with shipping comes in at close to $30k with their in-floor heating solution (not including concrete, stone, and sheets of wire mesh). Without their in-floor heating option, it would be approximately $22k (plus the concrete, stone, and wire mesh). ByggHouse WarmFörm foam would be somewhat cheaper (maybe in the $15′ ballpark without the stone, concrete, or rebar). But theirs doesn’t include an engineering stamp for my specific house. Iso-Slab would likely be a similar price to WarmFörm, and they do offer project-specific engineering for a fee.
– Thermal mass (the house will likely be orientated in a pretty ideal direction for taking advantage of passive solar)
– Simple/easy/quick installation
– Allows for easy and effective installation of in-floor radiant heating
– Could go with strong and economical polished/etched/stained concrete as the finished flooring
– Low-level entry points (ideal for an aging-in-place house)
– Potentially expensive
– Difficult to make plumbing/electrical repairs/changes
– May need to be kept heated in winter to prevent frost/freezing damage
– Harder floor surface may need rubber standing mats at kitchen sink and other places where a lot of standing takes place
Given the location of the property, I could probably get by with a vented crawl space for much cheaper. But I am not overly excited about that prospect. A conditioned crawl space with a shallow concrete floor might be getting me up close to the $25k to $40k price point of an SPFS slab-on-grade – especially by the time I calculate in framing and decking for the porches in place of the concrete patios.
– Easier access to plumbing and electrical under the floor
– Potential mechanical/storage space
– Might be cheaper than slab
– Wood is not as hard as concrete – a more forgiving surface
– Potentially shared air between house and crawlspace
– More excavating and more complicated installation (multiple concrete pours, etc.)
– Minimal thermal mass added to house interior
– Subfloor would need flooring installed
– Raised floor (built on top of the foundation stem walls) would likely mean building wood decks instead of using concrete patios on grade
– Need form material for footers and stem walls
What are your thoughts? What am I missing here? Are there viable ways to build an SPFS slab that are cheaper than the options I mentioned above?
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