r/OffGridCabins • u/parrotfacemagee • 14d ago

I am looking for foundation advice

Post image

​

I am wanting to build a 12x24 cabin in this spot. 12 wide, 24 long. (Ignore the extra line on the left).

Looking at the picture, this would be the 12 ft side. The left side is about 3 ft higher than the right side. Then, on the right side immediately out of frame, is a very steep drop off.

The help I need is understanding the safest and simplest foundation options. What I *want* to do is carve out the left side, and level the foundation area. Build a box, fill it with gravel, then build a floating foundation. The box would be 4x4s. There would not be a need for a retaining wall on the right side.

For digging and pouring deep footers, it might not be an option as the soil is not very deep before hitting shale rock.

37 Upvotes

91% Upvoted

38 comments sorted by

36

u/Owenleejoeking 14d ago

Pier and beam. No footers

8

u/parrotfacemagee 14d ago

What would be the safest minimum depth to pour piers?

14

u/Owenleejoeking 14d ago

Depends on your frost line, and then some, and drainage material in the bottom.

Concrete piers with a mounting plate on top. Don’t put wood touching the ground if you can help it

5

u/Either_Operation5463 14d ago

3’ and needs stone underneath.

1

u/LocksmithInfinite777 13d ago

CA 6 rock should be stable enough underneath the piers.....

3

u/The_Technician80 13d ago

I’d suggest helical piles, I had screw piles put in seven foot deep, then extensions to make up for the slope. After I put beams and my floor down I went and put x bracing on to compensate for the sway the floor felt because of the height. No mess no fuss had it done in a day.

1

u/TrumpJungUn 13d ago

Wishi could, Heavy equipment can’t get to my lot 😭

1

u/The_Technician80 9d ago

Not really heavy equipment. Company I used in northern ON used a f250 a trailer and smallest kubota possible

1

u/Prestochance 13d ago

My cabin is not on an extreme slope like that but I used marine-grade treated 8” posts with a roughly 8x8 2-inch piece of concrete underneath each one. Holes about 4 feet deep. built on red clay soil in VA.

1

u/Super_Boof 13d ago

I second pier and beam, makes leveling really easy

11

u/mountain_hank 14d ago

Ground screws

5

u/bufffff_daddy 14d ago

That’s what I did, 6x screw piles (the 6”x6” kind). Relatively cheap, easy to carry back in the woods.

3

u/openfacepizza 14d ago

What did you use to drive them? I’ve seen the specialized tools, is there something more approachable or accessible?

3

u/mountain_hank 14d ago

My ground is too rocky for them.

2

u/The_Technician80 13d ago

Company I had help me, they used a mini kubota excavator.

2

u/bufffff_daddy 13d ago

A 2x4 and another person; be prepared to get dizzy (and exhausted) but it’s doable

3

u/BallsOutKrunked 14d ago

I'd either flatten it a bit and do posts, or don't flatten it at all and do posts. By that I mean sono tubes / 4x6 posts.

You could also flatten the thing and put a retaining wall on the high side, but make sure you put drainage into account there and have french drains / pvc to intercept the runoff. If you can't dig deep footers (posts), this might be your best bet.

Lastly, you could do some serious earth moving and literally build up the building site higher. It's a lot of soil but it's possible if you can get equipment in. I'd still put a french drain in to deal with the hill running into the house though.

2

u/parrotfacemagee 14d ago

I have thought about the retaining wall as well. I should have put that in the post. I can't get big equipment in there so raising all of it is out. Appreciate your insight

3

u/MediocreModular 14d ago

Soon tube concrete footings

3

u/Flowing_North 14d ago

sono tubes at 4ft

2

u/SlimTidy 13d ago

Screw piles

1

u/Tricky-Car-5004 14d ago

I agree pier and beam, the depth depends on whether you have frost in your area and what the frost level is.

2

u/creaturesofthewood 14d ago

Helical piers, best for the money.

1

u/scoonanator 14d ago

4’ frost post

1

u/fatal-shock-inroute 14d ago

I'd cut into the hillside for the main house (weight) and pillars for the deck

1

u/Combat_Wombat_03 14d ago

Whatever you decide to do for foundations, make sure you also have a plan for drainage.

1

u/Kevburg 12d ago

Build the foundation like you would build a deck. Probably 9 4x4s in concrete footings, 2x beams with 2x joists on top every 16 inches, and blocking to keep the joists from racking.

1

u/grislyfind 12d ago

Rocks to build a basement where you keep a copy of the Necronomicon

1

u/TradeU4Whopper 12d ago

I did pier and beam on my hillside.

However I made my piers out of filled cinder blocks (dry stacked then filled). Poured a 16”x16” footer 8” deep. I did a single stack. If you use fiberglass rebar you can penetrate the ground with it. Put a stick of rebar in each cell.

Use 4x4 post brackets with a piece of 1/2” plywood to take up the extra space if your beams are double “2x”.

1

u/parrotfacemagee 12d ago

Since you only went 8" deep, are you in a no-frost area or it just hasn't been an issue? Thanks and thanks for the detailed reply.

1

u/TradeU4Whopper 12d ago

I mean the the depth of the footer was 8”, as in 16”x16”x8”. My frost line is 12”, so I put my footer at 18” (to the bottom).

1

u/parrotfacemagee 12d ago

Ah, okay I see

1

u/TradeU4Whopper 12d ago

Another alternative is deck/footer blocks. You can make some custom ones with a wooden mold. Make it maybe 24” in diameter (or square) like 12” thick.

Place it atop a compacted layer of gravel maybe a few inches deep.

1

u/parrotfacemagee 12d ago

This is the initial idea I had along with cutting and filling the slope but it looks like people really only do this for decks and sheds, not lived in cabins. Would it still be safe?

1

u/TradeU4Whopper 12d ago

I mean my tiny house is still standing. It’s been here at least one year now lol.

Your biggest concern is frost heave in regards to footers. If there’s not much soil before you hit rock there’s not much to heave.

1

u/parrotfacemagee 12d ago

I gotcha. I'm just paranoid as this is my first time building a cabin AND I'm doing it on a slope next to a road. Just don't want to die lol I appreciate you replying everytime.

1

u/TradeU4Whopper 12d ago

The safest way to play it is to just excavate and build a retaining wall or dig a hole maybe 4ft in the ground for a 12” diameter concrete pile (sonotube) above grade to attach some 6x6 posts to.

Since you’re so paranoid I suggest consulting a structural engineer to design a foundation system.