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hydrazine
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# Posted: 20 Aug 2023 03:28am - Edited by: hydrazine
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I'm building a guest cabin / outbuilding on my property. Plan was a 24x14' shed roof pier and beam foundation. I started digging my holes for the piers and footers (36" diameter hole with 30" footer with 12" sonotube) and ran into a problem. I planned to have 8 piers total, 4 per side. The holes for the front and back right most piers contain a lot of wood. I think someone buried stumps there and those end piers fell right on the edge of the stump dump.
I was thinking about shrinking the cabin and having it use only the 6 piers that have no wood. Center pier to center pier I'd have 16' which is a lot smaller than I want. I was thinking about cantilevering the beams over the end piers by no more than 2'. But this only really seems to be commonly done with decks. Thoughts on doing this with a cabin? The beams are going to be made from 3 2x12s. Being a shed roof cabin, the rafter tips and tails will land on the beams, so those two load bearing walls would be on the cantilever. I've read that it's possible for a beam to cantilever a distance equal to 1/4 the beam span, but I'm not sure what span this refers to. The span between piers or the total length of beam?
Unfortunately I don't have many good building sites on the property - I have another spot cleared already but it is earmarked for an eventual garage/shop. So this general area is where I'd like the cabin to go. It's the perfect spot, except for the damn buried stumps.
My other options is to shift the cabin the opposite direction of the stumps, and this may be possible but it puts it awfully close to some large trees so I expect I'll encounter roots over that way.
I've been trying to manually dig down to below the stump dump to virgin soil cutting wood out with a sawsall, but it is deep. I'm at least 10' deep and still encountering wood and it's starting to feel awfully sketchy . Other option is to get an excavator and remove them that way. If I can't cantilever this may be what I end up doing.
So yeah, do you think it would be safe to cantilever the beam and if so, is 2' acceptable? 1'?
Thanks a lot!
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gcrank1
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# Posted: 20 Aug 2023 12:00pm
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Oh, thats ugly 
Have done a good bit of grubbing, land clearing, pile burning and burying debris I say ya gotta abandon that side. You have NO IDEA what you are dealing with down there! Too bad you didnt start on that side; aint that the way it goes (sounds like you have my luck).
Shift to the other side?
Change the dimensions to get similar sq ft'age by going more to either end?
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hydrazine
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# Posted: 21 Aug 2023 07:02am - Edited by: hydrazine
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Yeah, bad luck...Took some more measurements today and I cannot shift the cabin dimensions over to the opposite side unfortunately. Don't have enough room.
Looking into finding a local engineer that will do a cheap consult to see if the cantilever idea will work. Perhaps making the beam out of 4 2x12s. Or a gluelam beam (not sure what's stronger) - I can get 5.5x12 or 5.5x15 gluelams or maybe a steel reinforced wooden beam? A pure metal beam seems kinda far outside of what I'm familiar with, but maybe even that?
Otherwise, if cantilever is a bad idea I'll just get an excavator and dig everything up. Pretty determined to make it work one way or another.
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Brettny
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# Posted: 21 Aug 2023 08:58am
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2' canalever sounds like to much for a tripple 2x12. In the end it may be cheaper to dig up that area down to hard pack vs getting a engineer involved.
Could you change the foot print to say 20x16'? You may need to add a 3rd girder but may also be cheaper than hiring someone to dig up unknown ground.
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spencerin
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# Posted: 21 Aug 2023 01:16pm
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Are you digging by hand? If so, why not rent, or hire, a heavy-duty mechanical auger to grind through it until you hit a solid footing?
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Cedar Fever
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# Posted: 21 Aug 2023 03:23pm
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My cabin is a hot mess. But it was built with a 1’ cantilever with 2x6 floor joists on double 2x6 beams and nothing sagged. I later added 2 more skids on the very outside and got rid of the cantilever.
What if you did a hybrid foundation? Do what you’ve got. Then pour some cement pads and put skids on the outside on blocks. So you have your piers, and on the outside it’s on blocks? Not a fantastic solution but I know all about compromises to get it done.
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Brettny
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# Posted: 21 Aug 2023 07:27pm
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When you mix tubes down to the frost line and blocks you get windows and doors that dont open in the winter.
How big is the building you have that 2x6 floor joist and 2x6 girters worked? How deep is the frost line?
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Cedar Fever
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# Posted: 21 Aug 2023 10:08pm
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My cabin is 16x24 and I try to keep everything lightweight. It’s in an almost desert environment, we’re at 41 days in a row 100+ degrees so it’s very rare to see freezing temps in winter. No idea what the frost line is here.
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hydrazine
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# Posted: 22 Aug 2023 12:04am - Edited by: hydrazine
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I started out with a skidsteer and 36" diameter auger. The auger would get hung up on the wood and stop spinning. I see online that there is a tree stump grinding auger attachment but I can't find one locally.
So from there I started digging by hand cutting wood out with a sawsall. I thought I could get down to virgin soil but the wood is buried too deep. I'll post some pics later, but 10-12ft down there is still wood and while I think I must be close, it's just getting too sketchy.
And thinking about it more, even if I got an excavator I think I would need to get new fill as the fill that comes out of the stump dump wouldn't be good. So I think I'm just going to abandon those piers and fill the holes back in and try and make it work with 6 piers instead of 8.
I spoke with an engineer and he said 2' overhang "should be fine". Going to follow up and see what he thinks for a beam. I'm thinking either 4 2x12s or a large gluelam. With a 2' overhang on both sides of cabin I can make my wall 21' (I had planned for 24' before I found the wood).
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hydrazine
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# Posted: 22 Aug 2023 12:08am
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Yeah I wouldn't have part of the foundation below frost line and part of it above ground. Not with our freeze thaw cycles.
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Brettny
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# Posted: 22 Aug 2023 06:10am
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Can you make provisions in the sono tubes to attach 45* 4x4s to the overhung section of the beam? Basicly an angle brace for under your girder.
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rpe
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# Posted: 22 Aug 2023 07:16am
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If you're down well below frost line (sounds like it), why not dump some gravel into the bottom, pour a big pad and build a sonotube or pier block pier on top? Backfill with gravel, and frost heave shouldn't be an issue. Settling over time might occur if the compostable material deep underground slowly collapses. That can be addressed by either shimming or using an adjustable saddle under the beam every year or two.
I know 'a wise man built his house upon the rock', but at the same time, you've got the take what the land offers you!
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gcrank1
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# Posted: 22 Aug 2023 12:19pm
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Ime the problem with shimming if/when required only becomes a problem IF you didnt prepare for the possibility. As said, build as good as possible with the access and expectation that you will need to keep your eye on it (laser levels are a great easy check tool).
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rpe
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# Posted: 22 Aug 2023 06:03pm - Edited by: rpe
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I'm with gcrank1. If I understand correctly, the piers of concern are at one end only? That should make it easy to access for shimming/adjusting if needed down the road. Planning is good, but it's easy to start over-thinking things and get mired down in endless distractions. I do that all the time!
As for sizing/design, here's a similar (identical?) sized building I put up a few years ago:
[url=https://www.small-cabin.com/forum/6_9967_0.html]https://www.small-cabin.com/foru m/6_9967_0.html
[/url]
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Grizzlyman
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# Posted: 23 Aug 2023 05:47pm
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I agree 100% that you want the best foundation possible… but it’s not like you are building a huge structure. My shed is 10’ wide and built on skids…14’ wide isn’t massive. If you dig downand backfilled with gravel I’m sure you’d be more than fine.. and could easily jack/ adjust if need be.
Also, if I understand from the picture- you want to have the beam stick over the post by 2’? I’m not sure why that would be a problem… especially since your beam is 24’ long. . Besides, the wall sitting on the overhang wouldn’t be load bearing- the rafters would go across the 14’ span for a shed roof.
I also think 2x10s would more than suffice for a beam.
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ICC
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# Posted: 24 Aug 2023 12:21am - Edited by: ICC
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Quoting: hydrazine try and make it work with 6 piers instead of 8.
So with 6 piers to a side what is the span between piers?
I agree with your assessment that if you excavated the pit you would need new fill. And that fill would need compaction. Also, would you have space to be able to dispose of all the material removed from the pit?
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