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vman14
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# Posted: 23 Jan 2025 09:14pm - Edited by: vman14
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I am hoping to start building a small cabin in the woods this spring. I am looking for any comments or critiques of my design. This was done using the SketchUp free version. I am just learning how to use it so please ignore the obvious beginner mistakes.
Sketch UP Link
EDIT: This is the floor framing with double rim joists
Things to know
I started digging the 6 holes for the 6x6 posts under the shed already. I was planning on just putting them in the ground without concrete but using roofing tar to protect from rot.
This is in Pennsylvania, the location is very rocky and I was only able to dig the holes about 24-28 inches deep. I understand this is not deep enough to reach the frost line.
The ground is not level. From one corner to the opposite corner there is about a 8-10" height difference. I plan on having the lowest corner a couple inches off of the ground
I plan on using LP smart siding and if I am successful may eventually want to insulate the walls and ceiling.
This is going to be a camp without water or electric and I will not be staying here long term.
My biggest concerns are
Is having only 6 6x6 posts in the ground sufficient for a 10'x16' cabin build using 2x8 floor joists?
Is it a terrible idea to not use concrete around the posts and is only going 28 inches into the ground going to make this fail?
Ventilation? I am not sure what I should to do prevent mold growth when not it use. I considered adding some sort of vent in one of the walls that can be opened when I am not staying there or possibly just leaving a window cracked.
I welcome any criticism and advice. I have never done anything like this before and thought it would be a fun project
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DRP
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# Posted: 24 Jan 2025 04:49am - Edited by: DRP
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It is not the concrete around the post that is important, it is the concrete or some type of spread footing under the post that is critical. Without a geotech and if its not a swamp, soil bearing capacity is usually assumed to be about a ton per square foot. A 6x6 is around a quarter of a square foot. Or, about 500 lbs capacity per post end. Look in either the foundation chapter of the code for footing sizes or at a minimum use footings sufficient for a deck by consulting DCA6 at awc.org.
The rim joists need to be sized to carry the load and span (they are not) and the front one is also carrying the deck.
The rear wall is correct, the other 3 have a kneewall unsupported atop an 8' wall. "Studs shall run unbroken from points of lateral support", in other words from floor to roof, eliminating the line of weak hinges around the building.
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vman14
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# Posted: 24 Jan 2025 09:37am
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Thank you for the reply. If I am understanding this. It seems like you are saying that the deck isn't designed properly and should be removed. If I removed the deck and made the front wall "unbroken" going from floor to roof would that solve this problem?
If I cut out more of the 6x6 post to add a second 2x8 to the rim joist under each of the walls, would that carry the load properly?
As for the soil bearing capacity. If I didn't add any spread footing to the current posts, would added another row of 3 6x6 posts spanning from one side to the other solve this issue? Or could I just add 2 more 6x6 posts, one on each side under the side walls since that is where most of the weight will be?
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gcrank1
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# Posted: 24 Jan 2025 02:16pm
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We have a 10x16 prebuilt shed (my toolshed) with a barn roof sitting on silo 'blocks', sometimes called a 'floating foundation'.
My '83-'84 build at 12x24 was also on silo blocks. And it is on a bit of slope not unlike your site.
The concrete silo staves are Not landscape (much smaller) blocks, they have a nice big flat weight distributing footprint. They can be found used in most areas.
But you have posts and holes already.....
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socceronly
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# Posted: 24 Jan 2025 04:10pm
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In my expert opinion, the dinosaur t-shirt is key.
Looks great, and this is really helpful for me as I am building a 10x16 in the spring.
Seeing it is great for a sense of scale.
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socceronly
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# Posted: 24 Jan 2025 04:18pm - Edited by: socceronly
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Can you build on skids instead of the posts? 8 to 10 inches isn't too bad. You could just use blocks.
Is this in Ontario? (every time I see 10x16 it seems likely).
I would separate the deck and the bunkie. Do them as two different things. Once you start attaching decks to buildings a whack of regulations come into effect.
Do it as landscaping as you don't need a permit for that. They often let bunkies go... but if you attach the deck it might complicate things.
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socceronly
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# Posted: 24 Jan 2025 04:22pm
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will this be 3 season uninsulated?
What is going on the exterior/interior walls?
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vman14
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# Posted: 24 Jan 2025 05:00pm - Edited by: vman14
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I based my cabin design off of a shed plan I found online here
URL
I enlarged it to 16' long and modified the foundation for 6x6 posts since that seems like the most practical choice given the slope it is being placed on. Vehicles cannot access the site since it is in the woods so leveling the ground and placing skids on gravel isn't really an option.
Would building this on blocks be better? I would have thought being on blocks it would shift more with the freezing and thawing of the ground.
The deck is something I would like to do but don't necessarily have to do so I may skip that for now. I figured having the platform there when building the cabin would be useful though.
The exterior walls will be LP smart siding since that seems like a longer lasting plywood than t1-11. The interior will be uninsulated for now. I am leaving the option to insulate later and will build in an area in the wall to allow for a stove pipe to pass through.
I modified the floor frame to include double rim joists in this link. Does this look right? Is 2.5" left on the 6x6 post enough to lag bolt into?
Sketch up floor frame only
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DRP
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# Posted: 24 Jan 2025 07:11pm
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Quoting: vman14 If I removed the deck and made the front wall "unbroken" going from floor to roof would that solve this problem?
Where you have a pair of plates at the 8' level, tuck them up tight to the roof. All studs run from floor to roof.
Quoting: vman14 As for the soil bearing capacity. If I didn't add any spread footing to the current posts, would ...
Here in the southern Blue Ridge we use 30 psf for snow and we've had that. I have no idea but wanted to throw some numbers at it to get a sense of the loads, at 50 lbs per square foot for snow and 10 more for roof dead load, the material weight, there's around 3000 lbs design load heading for each mid support, front and rear. A floor is usually designed for 40 psf live load and 10psf dead load, another 2000 lbs on the mid supports. ...I'm walking through how that part of the code works. The design load coming down to be resisted by the ground is around 5,000 lbs. Without a deck adding to that load. I wasn't saying it has to be removed I was pointing to the need for thoughtful design. I again threw a number at the problem, but a realistic one. We typically assume 2000 psf bearing capacity for good soil. You need 2.5 square feet of something hard that will contact the ground without whatever you put on it deforming or punching through it. Attach to that to prevent sliding or uplift.
Quoting: vman14 If I cut out more of the 6x6 post to add a second 2x8 to the rim joist under each of the walls, would that carry the load properly?
The design load would be the same on each section of rim so the question is what size beam do you need to carry 5000 lbs of uniformly distributed load over an 8' span. In #1/2 SPF it would be a double 2x12. The rim is not just carrying the floor, it is also carrying the roof.
For strength in bending, depth is what builds strength fastest. The "section modulus" of a 2x8 is around 13. For a 2x12 it is 32. A single 2x12 is stronger than a double 2x8. "Deeper is cheaper."
If the 6 posts ran from footing to roof a 2x12 could be notched in for the floor and another at the top of wall to carry the rafters.
I would solid sheath the roof with ply or osb to keep company from entering.
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gcrank1
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# Posted: 24 Jan 2025 07:35pm - Edited by: gcrank1
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A wood stove and its clearances takes up Huge space.
Ive only had experience in s-central WI, glacial sand/gravel ground, and using the silo blocks have worked well. Ive had some settling more than any 'heaving' that I can tell and that can easily be addressed by some hydraulic jacking and shims. And that not much or often.
Oh yeah...and Im no 'expert'
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Brettny
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# Posted: 24 Jan 2025 08:27pm
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10x16'..I would put it on blocks. Not worth the effort of building a frost free foundation for any building that small in our area. I'm in central NY.
I cant see any plans you posted but 2x8 floor joists are plenty strong. Put a trippled up beam/runner up each side, set them on blocks and your set. Even trippled up 2x6 would be fine for runners on that.
I have a 10x14 in central NY that we used for a cabin for about 4yrs. Not on level ground and nasty clay. The door still opens and closes in all seasons.
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spencerin
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# Posted: 25 Jan 2025 11:28am
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In this situation, I'd build a block foundation. An 8-10" change from front to back is nothing. With good drainage around the blocks and otherwise proper block laying, you shouldn't need to worry about frost heave.....
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neb
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# Posted: 25 Jan 2025 12:55pm - Edited by: neb
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Exciting times with your new cabin journey. I have a 10x16 back up in a canyon and a 16x16 I built last August. One in back country in buried utility poles and this one is built on blocks. I used 4x5 Xarms for trusses and did also on main frame of cabin. I like this build on top of ground better than poles buried.
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neb
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# Posted: 25 Jan 2025 01:08pm
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Wrap was used roof and sides.
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neb
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# Posted: 25 Jan 2025 01:18pm
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I won't insulate either but always can down the road. With this small stove it is very easy to heat. Nothing to get it 80 plus if I want too. I did vent the continuous roof ridge. Mine is really tight which is a good thing but still good venting which is important.
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neb
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# Posted: 25 Jan 2025 01:21pm
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Good Luck on your build and I will be looking forward for your new adventure. I have a ranch and these two cabins I have are a place to warmup and enjoy when we are there working or for outdoor activities.
Both places are snow blocked most winters and one way in and out.
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gcrank1
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# Posted: 25 Jan 2025 01:36pm
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And after the build comes the whole fun off-grid living stuff 
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spencerin
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# Posted: 25 Jan 2025 05:05pm
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vman14, what county in PA?
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vman14
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# Posted: 25 Jan 2025 11:44pm
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Being built in Perry County.
I am starting to think I would be better off scrapping my plans for building on posts and going the block route. I guess just rectangular concrete blocks are what is being suggested here and not deck blocks.
Maybe 3 pressure treated 16' 4x4's with 3 or 4 blocks under each? Then placing the 2x8's on top
I just don't like the idea of the lowest corner of the cabin being a minimum of about 11" from the ground
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Brettny
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# Posted: 26 Jan 2025 06:57am
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Quoting: vman14 I just don't like the idea of the lowest corner of the cabin being a minimum of about 11" from the ground
What's higher up going to accomplish?
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DRP
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# Posted: 26 Jan 2025 09:51am - Edited by: DRP
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Quoting: vman14 Being built in Perry County.
44 lbs per square foot snow load for your beam sizing.
This is a good app for snow loads etc. Your risk category is 1, (4 would be a school or hospital.)
https://ascehazardtool.org/
You mention not being able to dig easily. I'm further south on the same rock. A digging bar and tile spade are pretty much standard on every farm here. If you see fences the holes are usually 3' deep, to hold up wire. Then look at how many holes that farmer dug. I typically make my holes 2' square which gives room for most footings and room to work the shovel. Since I do this for a living, my footing depth is inspected. Early on I would rent various electric jackhammers and drills in tough ground. PA frost depth varies but runs 36-48"
Below was one project. The post is holding up the corner of an old farmhouse as we built a basement under it. The red tool is a Hilti percussion hammer drill, the one on the right is a Makita brute breaker electric jackhammer. I used a Vevor electric jackhammer that was in between sizes on the current job.
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gcrank1
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# Posted: 26 Jan 2025 10:43am
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The 'benchmark corner' on my old 12x24 build was the high elevation, compacted the sand/gravel, put down a silo block with a landscape solid block on top then the base beam. Btw, do put a piece of asphalt shingle between concrete and wood.
All of the rest of the 'piers' were spotted to the footprint and rough line leveled; ie, same silo block base and stack LS blocks upward. Once the deck was built I used a construction transit to level the deck (only because I had one to use).
Get The Deck Straight, Level And Square.
With my 10x16 toolshed a couple years ago it was very similar but with more 'piers' though I leveled the site (which wasnt bad), compacted and set blocks.
Though I never had significant issues with #1 it had grown, and thus became heavier, than I ever imagined.
I wished I had more piers! So on the toolshed I went overkill, No regrets.
On May1, 2024 we had our new pre-built milled log cabin 12x28 brought in to our new-ish land.
In prep I rough leveled the site, compacted the 'runs' where the beams run under the structure, then brought in crusher-run limestone (I have a little JD1025r c/w bucket) and made the two gravel runners (~12"+) 4-5' wide. Those I compacted (by driving the tractor with a full bucket repeatedly) then leveled out by man-rod and transit.
The silo blocks are 9 to a 28' side, 18 total (and calc at 2sf/block, 1 ton/sf, so 36ton); there is a gap between each block, maybe 5-6", I just eyeballed that once the corners were placed. I picked the corner I wanted to use as the benchmark and laser leveled all those blocks for height above grade and x/y. That is futzy and handwork with 80# blocks.
The beams under the cabin sit right on, centered up and almost like having a solid poured foundation.
There is accessible crawl space underneath for potential future improvements or maintenance.
Btw, I bought the used silo blocks locally for $2@.
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vman14
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# Posted: 26 Jan 2025 02:27pm
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Quoting: Brettny What's higher up going to accomplish?
I am hoping to go lower than that
Quoting: DRP 44 lbs per square foot snow load for your beam sizing. This is a good app for snow loads etc. Your risk category is 1, (4 would be a school or hospital.)
Ground Snow Load, pg 52 lb/ft2 for my location
I dug my holes 24-28" deep using a digging bar post hole digger, auger and a rented demolition hammer. I am not sure if I want to dig them out any deeper. Looking at frost depth maps, I estimated mine to probably be around 40". Maybe building on blocks is the way to go.
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spencerin
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# Posted: 26 Jan 2025 04:07pm - Edited by: spencerin
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Use 4" x 8" x 16" solid concrete block. And I know 11" above ground on the lowest corner means 19" to 21" on the highest corner, but that's not that bad.
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vman14
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# Posted: 27 Jan 2025 02:12pm - Edited by: vman14
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URL using 4x8x16 blocks
Would this be a better and sufficient foundation?
How much cantilever span is appropriate for a build like this?
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gcrank1
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# Posted: 27 Jan 2025 07:55pm
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Concrete silo staves: 10"x 30"x min 2" thick (think mine are 3.5"?)
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spencerin
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# Posted: 27 Jan 2025 08:16pm
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Sufficient foundation, yes, but I would rotate the block piers 90*.
As far as an acceptable cantilever span, that's subject to several variables, and thus best answered by an engineer. But, honestly, I would find some pre-built shed/cabin shells in your area and measure those cantilever spans for a starting point. You'll be adding weight to the walls, yes, but being a small cabin, you're not going to be adding that much, relatively speaking. Again, that's a good starting point.....
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DRP
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# Posted: 27 Jan 2025 11:46pm - Edited by: DRP
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The codebook is your friend there. the tables and figures are "prescriptive" stuff we've built so many times that if you follow the recipe the engineering has been done and it works as described. In this case I can think of 2 prescriptive answers. The first is, no further beyond the support than the depth of the joist. On this building I would use that one.
I'm going to explain the engineering behind that and use it again in a minute. In most cases the load is assumed to flow at up to a 45 degree angle. There is no bending, shear or anything going on, its just compression.
Same logic in the footing code, which is what your blocks are. A footing projects beyond the edge of what is sitting on it no more than its thickness. There is that 45 degree angle of safe compression again. Turn the blocks the other way and they go into bending and snap.
It'll also reduce the span of the skids to run them longways. Omit the center runner, you don't want it and can't relevel it. If the outside runners are 6x6 treated with the spans now at under 4' the load per span went down. With the cantilevers the joist spans were reduced and there is a little seesaw moment going on there helping as well. More reason to omit the center skid.
The role of the foundation connection is to resist loads from up, down and sideways. You'll blow over. (and you want to tuck the bearings under you further :confused That's why I omitted option 2 above on cantilever. Anyway, resist that potential with a mobile home anchor at each corner. Good luck screwing them in from the sounds of it.
All joints occur on a support, use 16' 6x6's.
You can get 8" solid blocks or the larger landscape blocks most places. For that matter you could line up 2@ 8' precast lintels on each side, concrete screw a 16' treated mudsill on it and go to town.
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