I'm looking at starting a workshop for myself; probably 32' x 40' x 12'. (though technically, it's going to be a "Sugar Shack" with a boiling room and considered an Ag building because then I can skip the building permits)
My issue is that the area I'm looking to build on is wet, with silty sand under the topsoil (it's along a creek). It's not officially in a flood zone, because the area has never been mapped by FEMA, but if it ever is mapped, I'm going to assume based upon the last really major flood I saw that it's about 2' under the 100-year flood line. What I'm going back and forth on now is what kind of foundation to use. My options as I see them are:
- Continuous concrete footer with a 2'-3' stem wall (basically creating a crawl space) and a wood platform floor.
- Continuous concrete footer with a bunch of fill to put in a concrete slab floor.
- Techno Metal Posts (helical piles) for a post and beam foundation with a wood platform floor.
I've determined that even if I add fill to get high enough, a monoslab foundation isn't ideal for the size building I'm looking at on this kind of soil. Everything I've read seems to indicate that I'd be begging for shifting and cracks over time. But if you have enough experience to tell me I'm probably overthinking it, a monoslab would probably be the cheapest route for me since I could pour the slab around a pile of fill then backfill to get the footers deep enough to not freeze.
My goal here is to build as much of this as I can myself, though I've accepted that for the foundation at least, that will probably only extend to site work. At this point, I'm strongly leaning towards the pile and beam foundation because issues like drainage basically go away except for access concerns. Plus, with a totally elevated building, I don't have to deal with keeping pests out of a crawl space. Though obviously, an elevated structure has fairly important requirements with regard to air sealing and insulating the floor.
Anyone want to dump additional considerations on me here that might shift things one way or the other?
Do you have experience with Techno Metal Posts that might be relevant?
Any other suggestions for methods I just appear to be ignoring completely?