[wahern]

I don't think the cantilevers are innovations. Here's a description and explanation of cantilevered footings from a 1924 book: https://www.google.com/books/edition/Reinforced_Concrete_and...

I'm guessing the issue here isn't that these techniques are innovative, it's that they've done their homework and the tolerances are tighter. If you construct them properly, they're more than sufficient. Emphasis on if. An inspector can't just walk in and eyeball something using his 30 years of experience to judge adequacy.[1] That's the problem--the classic tradeoff between administrative efficiency vs accuracy.

[1] The irony is that an inspector circa 1950 probably would have been able to do that.

[m0llusk]

The interesting problem they solved is building with cantilevers efficiently in the context of a small home. Historically cantilevers were considered exotic and expensive with Frank Lloyd Wright's Falling Water being one of the few well known examples of residences using cantilevers.

[wahern]

Those are a different kind of structural concrete cantilever. Look at the pictures of the various houses this group has built. What they all have in common is that: 1) they sit atop tall concrete or block columns on 2) uneven terrain and 3) otherwise use straight-forward, typical wooden beams and joists for the flooring (yes, they might cantilever some, but that's neither new nor uncommon).

I'm no architect, but I think the cost savings as compared to modern techniques (but very much, if not exactly, like older techniques) is the avoidance of 1) clearing and leveling the land and 2) pouring a huge reinforced concrete slab.

Before the advent of hydraulic bulldozers it was just too cost prohibitive to clear land and pour big slabs for mass-scale housing. Instead, you would pour (or build) some small footings, and then lay some beams on the footings, possibly elevated by some short columns (or simply stones or concrete blocks). But unlike what would be common for cheap housing 50-100 years ago, building codes won't allow you to build a whole house on simple footings like that because of the potential for ground instability exacerbated by uneven weight distribution and uneven weight-bearing capacity of the soil under each footing.

But what you can do, apparently, is use "cantilevered" footings tied to a small number of deep, robust, secure pads. Those pads are what guarantee the house won't move, and all you need are some shovels and a pick-up truck, and you don't even need to level any land. You then "cantilever" some simple concrete footings off those pads using reinforced concrete beams (which I bet are probably flush with the ground and look like a gratuitous use of concrete). I'd bet money that such cantilevered footings are what are underneath many or most of those columns you see under those houses, the rest of the columns sitting directly atop the pads.

[megameter]

This sounds approximately right, though I would love to see a real explanation from the creators.

It signals another example of changing practices in this century due to new ideas around materials accompanied by precision machine crafting. Cross-laminated timber, for example, is very hyped now since it can withstand huge loads and charring while still being a cheap and familiar "wood, glue, preservatives and pressure" composite, capable of being shaped into panels, arches and doorframes out of the factory with a CNC machine for reduced build times. Yesterday I saw a video of a CLT passive house built in Australia: The build, while not aiming for cost, was made simpler in design by having the load bearing parts of the structure also handle most of the insulation, and it put up impressive test numbers.

[wahern]

Maybe I'm overthinking it and/or maybe the article is using an idiosyncratic meaning of "foundation". The article says "The foundation of the Tiny House uses cantilevers, seesaw-like joists that help save wood and concrete and actually make the house stronger than a typical foundation would." Which might be a fancy description for basic techniques[1] used to build countless old houses in Alabama and elsewhere, some of which I got to crawl under or around when working summers with my Dad, who did remodeling and other contractor work in Alabama, Florida, and Louisiana. Not all those houses had footings directly underneath the permitter; the joists and walls might cantilever, while the footings were still basic and not tied together like with the cantilevered footing system. Although the cantilevers might be more extreme in these new designs.

Unfortunately, I can't find any technical material on the school's website. Here's the page for the various homes: http://ruralstudio.org/project_tags/20k/. Notably, some of them do seem to use modern concrete slab foundations, and at least one of the pictures shows a bulldozer in the background. Looks like they have a bunch of different designs.

[1] Basically just like people build decks today. Of course, lots of decks are dangerous, shifting and collapsing, precisely because the techniques aren't very forgiving of mistakes or poor siting.

EDIT: Here's a blog post with a better description, which seems to be discussing the same house(s) depicted in the Fast Company article: "Siteworks are a major cost item and cantilevering the floor joists past the foundation piles reduces the area of siteworks. ... Cantilevered floor girders act more efficiently as beams, making smaller and less expensive timber sections sufficient. Floor joists are cantilevered from the girders for the same reason." https://misfitsarchitecture.com/2016/08/31/architecture-misf... So it seems the usage of "foundation" in the other article was misleading. And these definitely aren't new techniques, not if you count the stock of 50-plus-year-old homes built in poor, rural America (i.e. not simply the stereotypical New England farm house). So presumably what's innovative is that the students have done the proper analysis and testing to refine them, ensuring they behave as intended as well as meeting modern standards of safety and reliability.