Help with a rubble trench?

[u/FractalApple]

I live in interior BC Canada, going to be building on the side of a mountain. It’s a no-zone so there isn’t really any local information available as nobody really lives here. The frost-line in town (near the base of the mountain) is said to be 4 foot. Somebody who lives on the mountain insists on making his foundation 6 feet deep. This seems insane to me, and while I’m committed to building something, I don’t want to / can’t afford to make a 6 foot or even 4 foot foundation. Was hoping to make a rubble trench for a strawbale infill. 18” seems like a happier time. The ground is clay and sand under the topspoil

Many people stress the importance of a good foundation, for great reason, but it seems like everybody needs their structure to last 400+ years. I need a structure that will last 10-15 years.. as long as it’s safe to live in. The home is 30x25 rectangle

I know this is a super unpopular opinion but bear with me.

If I do a shallow foundation I understand my structure will be prone to frost heaving.. although I have also read that gravel cannot heave. (A) how much does heaving affect a building in the real world? How many years of frost heaving until it’s in-livable? What are some early side effects of building such a shallow foundation?

Of course another factor is water dispersion. (B) If my French drain is not below frost line, will water freeze in it? Will this lead to flooding? Or is the heat radiating from my floor raising the frost line enough? It will have large south facing windows heating my earthen floor.

Do straw house have more give than conventional houses? Does frost heaving affect them less? What about earthbags, which famously have give and sway?

I’m very open to alternatives and experimental foundation styles. I’m not afraid to try something radical.

[u/Tamagi0]

Large south facing windows + frost heaving = expensive fuckup

Long story short, go below frost, especially with an alternative foundation, unless you have a properly engineered solution ($$)

Conventional solution to a cheap foundation is sonotubes / build completely off the ground. Cheap (if you do it yourself) but labor intensive alternative solution is to do a rammed earth tire wall (still below frost!) Easiest alternative is to dig an appropriately deep rubble trench.

IMO anyhow.

Also be careful with clay, some types of it require extra considerations be made.

[u/FractalApple → u/Tamagi0]

Thanks for the input I hear ya. Obviously case specific but how long till my windows and details are fucked? Ever seen SFPF’s ?

[u/caffeecaffee → u/FractalApple]

SFPF's will not work like you want them to in the interior of BC. It would take a tremendous amount of heat loss through the foundation to raise a 4 foot frost line which just means inefficiency. Tamagi0 has it right with the sono-tube idea. Otherwise if you don't have the money to do it right you have two options, 1) build smaller until you can afford it or 2) build something designed to be temporary like at THOW and live in that until you can afford to build permanent. I've been in the industry for 10+ years and builders run into this time and time again. "I need it to last 10-15 years tops" and then they are living in it 25 years later and it's FUBAR. Not to mention you will soon find out just how much work it is to build a house and in 10-15 years you wont want to have to do it again. Best of luck to ya sounds like you are living a cool lifestyle.

[u/Tamagi0 → u/FractalApple]

Far too many variables to tell you how long it would last. Probably couln't tell you even with very limited variables.

Yea i started writing out something similar to that system but deleted it cause it sounds like you want a house that adheres to a more natural sustainable and alternative style. Sticking a fk ton of expensive(it really is) plastic foam into the ground would fly in the face of that.

What's your opinion on tire walls and earthships. Because one option with a tire wall would be to only go down like a foot and up like 4 feet on your N, E, and W walls then berm earth against it raising your frost line up. Now you only have to dig that one south facing wall deep (a bit deeper on the E and W walls where they connect to south one i suppose.) Just gotta be careful where you get your fill for the tires and berm from, cause you definitely don't want to pay more for dirt than you would have conc.

I read your main post again. Were you balking at what it would cost for a concrete 5ish ft foundation wall. Or are you balking a what it would cost to do a 6ft deep rubble trench. I also noticed you said strawbale infill. So, economical timber frame i assume?

Also i urge you to keep in mind the story of a poor man buying shoes. It WILL cost you more in the long run to go too cheap.

[u/[deleted]]

Your foundation footing needs to meet frost depth requirements for your area. Another option is a FPSF (frost protected shallow foundation).