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Pole Barns and Post Holes
Thanks for the note Bob. You mention the problem I also anticipated. Only I wasn’t thinking about leakage as much as wondering if frost heave would break something if the two roofs were solidly joined. I've seen buildings with basements here that were virtually destroyed by frost heave when left unheated for a winter or two.
I guess it would be great to eliminate the overlapping roofs all together. I sure thought about going straight up next to the garage. The rafters probably can be turned around. an increased span would result, but that's probably manageable.
There always seems to be a 'But Then' problem. But then, going straight up, the shed wall would be higher than the garage wall and snow would drift into space and couldn't be easily removed. That's probably a loading question, and an experienced builder could design something that would work and reinforce the garage if necessary. That might be the easiest solution.
At the moment, I have some vague ideas that keep the overlapping roofs idea. In effect, they amount to building part of the garage into the new shed and joining them in a soft way to be relatively weather proof but so they wouldn't tear each other apart. It's safe to say that what I come up so far ranges from 'probably not viable' to 'simply dumb.' I suppose floating both structures and joining the adjacent walls might be easiest, but I'd sure hate to give up the pole construction plan.
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Pole Barns and Post Holes
I live in a frost area (northern VT). I've had good luck building pole barns and sheds that don't move by using pyramid shaped posts. I make a form with plywood, make sure the bottom of them is below frost and the top is above grade, and fill them with concrete. I generally make the bottom about 18-24" square, tapering up to about 10" square on top. By making pyramid shaped forms, when the ground freezes and lifts (like it always does), it will lift away from the post. I've tried sono tubes, pressure treated posts with slippery covers on them, and a pipe within a pipe. Nothing I've tried works better than these pyramid shaped posts.
Corm
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Pole Barns and Post Holes
FOr my 40x60' barn I used Treated 6x6" poles that I sunk 30" deep into the ground by just using a post hole digger. At the bottom of the holes I placed a round concrete footer that was about 16" in DIamet and 4" thick. On the outside edge of the poles I nailed a 4"x6" piece of treated lumber about 12" from the bottom to give it an edge that would have to displace ground if it were to try and heave. NOt sure if that made any difference, but after 3 years there has been no movement yet. I live near St. Louis MO so aour winters usually aren't too severe, but we do experience about 6 weeks of at or below freezeing weather.
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Pole Barns and Post Holes
Thanks for the notes. I'm still getting my ideas together about pole construction. It's a brand new idea for me that a building on poles below frost (4'+ here) still move. Most design books I've read say the poles have to be below frost, so I guess I assumed that they wouldn't move. That's why relying entirely on book learning is risky. Maybe tying the garage and new shed walls together and then joining the roofs together is a viable design. I would still check with people who've done a lot of building here to see what works best though.
The pyramid idea to keep posts from heaving is interesting even if I end up wanting my posts to move. I guess a pyramid reduces the amount of concrete needed to get enough post in concrete so they won't pull out. Perhaps the shape also reduces the chance of the concrete cracking and releasing the posts. It sounds like you guys have got augers bigger than my 12-incher to do some of this stuff.
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Pole Barns and Post Holes
Here in Western Wis, we had a relatively cold winter and little snow cover. Frost went down 60" in some places.
I'm building a 16"x24" storage shed this summer. Haven't decided between pole barn approach or concrete piers/frame construction. Don't plan to go down further than 4' either way.
jim
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Pole Barns and Post Holes
Jim: We had a cold winter too but with fair snow cover so the frost didn't go too deep. I've got to get back to my own shed ideas. Our neighbour's well line did freeze and I know it's 5'+ deep because we dug up the old head to install a pitless adapter last summer. I wonder if the exposed well casing caused the freezing? Ours didn't freeze but the casing gets covered with snow.
When I read your comment I looked at Corm's previous post. That might be something to think about but I guess the bottom of his forms would have to go below frost. I wonder how Corm gets 24" squares at the bottom of post holes?
In my case, my shed would attach to an existing garage that I think floats on the frost so it probably would be better if the shed did as well. The house we demolished at our camp floated on frost for 40 or more years, as do many of the older buildings around here. Floating them does work if it's consistent with codes. Frost heave wasn't the reason for demolishing the house. I saw somebody in town last week doing about what I want. However, it looked like he had just cut rafters to the angle of the garage roof and was using post and beam for the other ends. He seemed to be applying the rafters directly to the shingles on the garage roof. Maybe things are simpler than I think.
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Pole Barns and Post Holes
Tom,
A lot depends on the soil your putting the poles in. Paul Fox hit the nail on the head. Dig down below frost to set your pad, set the pole on the pad and backfil with a material that water passes through. When the frost penetrates it doesn't have anything to grip.
I live in frigid northern Michigan where winter can and often gets pretty nasty. Up until a few years ago (until local counties acceptance of the national codes) most footers went down only 24"...They never moved around because most of this area is sand....Maybe it's a regional thing, but most of the local builders still swear by that old method...I personally subscribe to the 48" (below frostline method), but in the middle of sub zero January when your vehicle gets stuck, you can go to the side of the road and dig up some loose sand for your tires to bite on. Granted the snow pack insulates it to some degree, but we got snow late this year, where there wasn't sand the frost went deep, where it was you could be digging in short order.
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Pole Barns and Post Holes
As you stated before to freeze and cause damage you must have moisture.
Sand at the side of the road is not hard find if the climate is dry. In the Canadian prairies you can have dust storms in the middle of the winter.
This is related to putting your clothes on the line at -40 F and them drying in a few hours. The process is called sublimation. This is were a solid goes to a gas with out entering a liquid state. In the lab or food prep it is called freeze drying.
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Pole Barns and Post Holes
Randy: I believe that our old camp house as well as our new elevated shed bears out what you say. The old house floated on about 2' of concrete blocks and survived just fine even with a 5' cellar under the house. Nearby buildings with conventional foundations and basements that were left unheated over several winters almost destroyed themselves.
Our new 10 x 10 wash shed uses conventional framing built on top of posts and beams. The postholes are 4' deep and at 5' centres. We didn't use pads in the holes because it would have made leveling the beams tricky. Besides, a pad on the bottom of a 12" hole probably doesn't spread the load much more than the ends of the 6x6 posts we used.
I never was certain if frost can grab and lift timber posts or poles but frost barriers are now required by code for new residential construction. I think barriers must be installed on foundation walls and sonno tubes but I don't know about poles. The fact that our shed hasn't moved through three winters probably means that frost doesn't grab timber. Eaves on the shed are very wide so roof runoff is away from the posts.
Peters: In the AF in North Dakota we used to call that stuff 'snrt.' You know, snow and dirt. I guess snrt is easier to say than 'snust.' It was strange to be driving when snow was blowing across the highway, drive through it and then smell dust. We finally got rid of the last bag kiln-dried sand we bought to spread on ice. The building supply place must have left the bags stacked in a mud puddle because the sand was anything but kiln-dried. I can attest that wet sand freezes solid as concrete. We had to bring a bag inside several days before we needed to use it.
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Pole Barns and Post Holes
I did not read all of the replies on this one, so if this has been said I ask forgivness. Wrap a layer of tar paper around the in ground portion of the poles. This helps to prevent frost heave effect on the poles.
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