I'll try to make this concise. 1) Building a tiny house in Austin, TX as an ADU in the back of my lot in central Austin. Existing house is net positive (orig 1948 CMU 1,000 sf deep energy retrofit + 2012 stick frame 1,100 sf addition). 2) The lot has significant grade change over the site with limited access for heavy equipment for traditional concrete slab foundation. 3) Considering building with metal SIPs. Design still in flux, but probably ~21'x~13' with "shed" or "butterfly" roof. 4) Have thought about pier and beam foundation. Have considered helical pile foundation too (though I have no experience). Soil is mostly caliche (heavy clay). Not sure helical will work well. Looking for advice. 5) I built a small (800 sf) metal SIP (Structall) house back in 2007 so I'm relatively familiar with construction process. Foundation was a challenge then too. Advice on foundations? Advice on any local installers? Advice on manufacturer given location? Thanks. - Sunshine in Austin TX

Have you considered treated lumber (4x4, 4x6, or 6x6) piers set directly in earth? i.e. dig a hole and set a post or drive piles, or pour concrete piers and set posts on top of concrete like in the following examples:

Sunshine, the previous topic was exactly as you are describing your project a "tiny house" metal panels, floor walls, & roof on a helical pile foundation. project photos view-able at http://www.permathermsips.com

thanks for the suggestion, but wood is a challenging substructure in austin. moisture, the caliche soils, termites, etc. make older wooden pier and beam structures a thing of the past.

i saw that post. the photos on the site, however, are fairly low res. can you possibly send higher res photos of the steel structure? and/or any details for connecting the metal SIP floor to the steel substructure? the connection of SIP to substructure was particularly challenging when I worked on a project back in 2007. thanks.

and who engineered your helical piles? did you get a stamp?

Posted By sunshine on 26 Jul 2015 02:24 PM
and who engineered your helical piles? did you get a stamp?

yes I can send higher resolution photos if you want to PM your email to me?
I was not the GC on this job , just the supplier/installer. But can assure you the foundation as well as the entire structure would have been signed/sealed by engineer. I can get that info from the GC/ owner

My understanding is that helical pilings are only used where soil stability is an issue.

Posted By jonr on 26 Jul 2015 06:14 PM
My understanding is that helical pilings are only used where soil stability is an issue.

jonr,
not necessarily , the pilings in this case were used for economy
was a lot less expensive than a footer/stem wall

in my case, helical piles would be potentially driven by three issues. 1) cost. 2) difficult access for concrete pour. 3) highly expansive clay soils. concrete foundations in my part of town have to be quite robust to withstand the the moisture-driven expansions. kind of similar to frost-heave in the NE in some ways.