Steep rocky slope -- need thoughts on foundation

Started by RyanDe, September 05, 2018, 01:19:55 PM

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RyanDe

I want to build a bunk house here, probably 10x10 with two bunks for friends/family but the issue is not only is it steep but there are rocks everywhere making digging all bug impossible. I was thinking of pouring or using blocks on the rocks since that should be pretty stable but would like to get some ideas from other people.

https://imgur.com/a/sbGy3XG

This is basically the only place to build it so I need to get creative. :-)

ChugiakTinkerer

Welcome to the forum!

For the boulders that are large enough I would consider ways to use them as piers.  Move the smaller ones out of the way and incorporate the larger ones into your foundation.  For what is essentially a shed you won't need a perimeter foundation.  This assumes of course that the county inspector won't say otherwise.

You may be able to find commercially made anchors that will allow you to attach a couple of 4x8 beams to the boulders.  If not, you'll want to look into custom-made anchors.  I'm thinking of something that allows you to drill a hole using a hammer drill, insert an anchor and grout it in place.

One of the Owner-Builder projects is on bedrock: https://countryplans.com/smf/index.php?topic=14738.0

Here's a pic of the anchors he used: http://www.anglersparadise.ca/building-the-foundation/

For a small bunkhouse you should be able to make use of the larger boulders to the same effect.  I would try to get supporting beams level and anchored directly to rock.  Avoid using posts if you can, or brace them substantially if you must have posts.
My cabin build thread: Alaskan remote 16x28 1.5 story


RyanDe

#2
Thanks! What do you mean by not using posts? I'm assuming since it's not level that I might be able to anchor one side to the rock but the other side will have to be up on some type of post/pier to make it level, no?

Here is what I'm thinking, I've placed yellow bricks where the piers would go. The front would have to be about 4' higher than the back though.

https://imgur.com/a/RalQr3j

ChugiakTinkerer

Quote from: RyanDe on September 05, 2018, 03:54:45 PM
Thanks! What do you mean by not using posts? I'm assuming since it's not level that I might be able to anchor one side to the rock but the other side will have to be up on some type of post/pier to make it level, no?

Here is what I'm thinking, I've placed yellow bricks where the piers would go. The front would have to be about 4' higher than the back though.

https://imgur.com/a/RalQr3j

Looking at your second image, the front left brick is sitting near a large boulder.  My thought on trying to avoid posts would be to see if you can anchor the front end of a beam to the boulder.  For the back end of the beam, you may be able to dig down a ways so that you can put in a concrete pier roughly level with the top of the boulder.

Trying to use the large rocks as a foundation means doing things a little outside the norm, like perhaps your beams aren't parallel.  I would at least see if it's doable.  What you don't want is to have your bunkhouse sitting on some 4x4 posts that are inadequate to withstand any lateral force that could cause the posts to rack over.
My cabin build thread: Alaskan remote 16x28 1.5 story

Don_P

I'd dig/roll rocks out of that area enough to level a perimeter. You are sitting on what I suspect is well drained rubble, I doubt frost is a concern. You're surrounded by a field of flat cleaving rock. A few sacks of mortar and you could have a stone house.

There is a cliff at one end of my property, the base looks very similar with rocks from truck sized on down laying about. The boulders on those piles are not really all that stable. It can depend on what boulders they are laying on and what they are laying on.  I use the bobcat and mine that area for rocks while slowly flattening it as well. Switching back and forth from forks to bucket (they rent those things too) Never have found the bottom of the rock pile but they say the mountain was about 5,000 feet taller back in the day so probably like you, I don't expect to run out.

These were sticks and stones from one site, it looked much like yours when we started but interestingly there weren't a dozen small rocks in the ground, a weathered sandstone cap that rode on the surface.