Frost heave with posts in the ground

- Forums - Register/Sign Up - Reply - Search - Statistics -

Small Cabin Forum / Cabin Construction / Frost heave with posts in the ground


Author	Message
justins7 Member	# Posted: 8 Sep 2020 11:59am Reply I am in upstate NY. The frost line is at least 6-7 feet deep here. I have had problems with the cabin I bought â€”Â frost heave has jettisoned three piers out of the ground (apparently years before I bought it). Those three piers were not buried deep enough. So I am aware of the power of frost. But: What happens with other things like posts or cinder blocks buried much closer to the surface, like 8-10" deep? Will those get heaved out as well? Or is it really only a problem with larger structures like concrete piers buried deeper (to where they didn't go below the frost line)? I am burying some cinder blocks with posts in them basically flush with the ground (8" down). It's way too difficult for me to dig the full 7' down by hand since it's so rocky here and I don't have a back hoe. So I am wondering if this is going to just get heaved out by ice â€” or maybe it won't since it's still close to the surface. Experiences?

Brettny Member	# Posted: 8 Sep 2020 03:52pm Reply How deep are the current ones? Where in NY is the frost depth 7'? No blocks will act just like your piers did if not buried deep enough. A cabin on blocks on a gravel pad will still move. This may mean cutting the door to make it open or re leveling the cabin each spring. To many factors to really tell.

justins7 Member	# Posted: 8 Sep 2020 04:15pm Reply I should've been clearer (I wrote that too early this morning). The posts are just really for fence-posts, not intended to be structural. I am just asking if everything gets heaved out of the ground? (Even just one cinder block on its own, buried only 8" deep.) I secured a post into a cinder block with concrete, and buried that 8" to the top of the block. Will that also heave out?

ICC Member	# Posted: 8 Sep 2020 08:36pm Reply Anything that has water freeze below it will lift; fence posts, blocks, etc. The freezing water does not discriminate, it just expands. Depending on what ele may move the post, etc. moves a lot or a little.

toyota_mdt_tech Member	# Posted: 8 Sep 2020 09:22pm Reply Quoting: justins7 I should've been clearer (I wrote that too early this morning). The posts are just really for fence-posts, not intended to be structural. I am just asking if everything gets heaved out of the ground? (Even just one cinder block on its own, buried only 8" deep.) I secured a post into a cinder block with concrete, and buried that 8" to the top of the block. Will that also heave out? Justin, here is how I deal with it. Did a hold, 3 feet deep or whatever. Flare it out at the bottom, dump some gravel in the botton, not use a sono tube for your post. When you pour concrete in a hole, it conforms to the irregular surface of the hole, this locks the soil onto the concrete, when it freezes, it lifts it all up. Its even worse for those guys who like to add the large flared out concrete cap on the top. With the flare at the bottom and a sono tube, the flare keeps it from lifting out as its also frozen in, the smooth sides of the sono tube reduce the grounds ability to lift it up. This is the best option short of going below the frost line and even then, the frozen ground could still lift a post if you dont do the sono tube.

KinAlberta Member	# Posted: 9 Sep 2020 02:16am - Edited by: KinAlberta Reply At the lake we have several buildings on blocks including a boathouse very close to the water level. Thereâ€™s been no heaving at all. My guess is that the ground freezes evenly across the base and everything rises in unison. Also in our city there are thousands of old detached garages on concrete pads. The ground here is mostly deep clay. The concrete floors in these garages frequently cracked and maybe heaved up an inch or so but I have never heard of any significant heaving. A gravel base that removes top soil will help drainage but even 6 or 8 inches of soaked soil wonâ€™t expand all that much (maybe 1/2 an inch to less than an inch Iâ€™m guessing). Enough to eliminate concrete cracking maybe and also to reduce the risk of uneven freezing that you could have without a gravel base. However beneath the gravel you may still have a lot of depth of ground that can absorb a lot of water and that can expand a lot. I figure thatâ€™s where the large movement/expansion originates. Read this and note the comments on â€œice lensingâ€ Foundation frost heaving https://woodgears.ca/cottage/foundation.html

Brettny Member	# Posted: 9 Sep 2020 07:20am Reply 1/2in may seam minimal but it's enough to stick windows and make a door inoperative.

justins7 Member	# Posted: 9 Sep 2020 12:39pm Reply Thanks for all the info. toyota_mdt_tech â€”Â that makes total sense. I'll try the "flaring" method. I know all too well about frost heave. As I mentioned in the first post, my cabin has it pretty bad on one side. The piers are sticking out like tumors. Apparently they failed to pour the concrete deep enough on that side (my neighbor even remembers that there was a stop-work order placed back when it was built 25 years ago. Apparently it was ignored.) They also didn't use smooth tubes, so the piers are super "gripable" and coarse. When I bought the place I didn't know about this phenomenon and just assumed the cabin had settled, which explained the tilt. (I am still really pissed that the inspector failed to note the frost heave. I complained to him later but he shrugged it off.) Now there is little to be done other than propping up the OTHER side of the cabin, unless I get back hoes to pull those piers out. It's a nightmare that can't easily be resolved. All that being said, I was really asking about fence-posts and the like. I am building a firewood shelter and do not have the resources to dig that far down right now, so I am trying different methods to see what works. It's really not a big deal if the shelter moves around a bit â€”Â I'm using wood harvested from the woods, and I can just adjust it as needed.

NorthRick Member	# Posted: 9 Sep 2020 12:41pm - Edited by: NorthRick Reply Quoting: KinAlberta At the lake we have several buildings on blocks including a boathouse very close to the water level. Thereâ€™s been no heaving at all. My guess is that the ground freezes evenly across the base and everything rises in unison. Our cabin sits on blocks that are at the surface. I built in a method to adjust it if needed but have never needed. The porch on the front of the cabin is a different story. The outside end of that is supported by posts that go 3' into the ground. Things were just fine for years and then one winter they got pushed 8" out of the ground. I fixed that and haven't had problems since. I'd either install a post/foundation the way you are supposed to or keep it all on the surface.

rpe Member	# Posted: 9 Sep 2020 08:59pm Reply I'm in the process of building a workshop/storage shed, 14'x24'. It is designed to sit on two pressure treated beams, each supported by 4 piers. This is a frost-heave prone area, so here's what I did. I was able to get to bedrock on four of the piers, with hole depths ranging from zero (surface bedrock) to about 4'. Those four piers were poured using sonotubes with rebar reinforcements tying into the bedrock. The area around the sonotubes was backfilled with coarse gravel. With the other four holes I could not get to bedrock, and gave up at about the 6' mark (1' below frost line) when I hit loose rock and gravel after several feet of clay. I used some galvanized screw piles instead of sonotubes for a couple of the holes, as the stem of the pipe coming up to the surface is much smaller in diameter, and hopefully less affected by frost movement. To keep the screw piers in place, I poured the equivalent of a couple bags of mixed concrete into the bottom of the hole, and worked the screw pile into the concrete mix at the bottom of the hole. Then it was leveled and held stationary overnight. Once cured, I back-filled the hole with gravel/sand mix again, to keep the evil clay some distance away. On two of these deep holes, I was unable to get the screw portion of the screw pier down far enough into my hole, due to large rocks protruding into the hole. I ended up using 2" galvanized pipe with rebar cross-pins at the bottom and fiddled it down around the rocks. Again, set in concrete, and then back-filled with gravel. Sorry for the long-winded story, but our area is full of pier nightmares, due to cold winters, clay soil, and lots of near-surface ground water. Being water-access properties makes the challenge even greater. This particular build project was a bit of an experiment, as I've not heard of others using screw piles in the manner described before.

rpe Member	# Posted: 9 Sep 2020 09:14pm Reply Sorry, got carried away and didn't finish the reply. Given you've already experienced heaving at the site, it is very likely any solid objects in the freezing zone will experience the frost heave effect. I know you mentioned the difficulty of digging deep enough to get below the frost line. I've struggled with that as well, and ended up using steel wrecking bar to pound into the hole to loosen the soil/rock at the bottom. A shop vac was used to suck out the contents of the hole, and lift out any small/medium sized rocks. It's a slow process, but I got down 6 ft that way. Now whether that effort is worth it for a fence post, I'm not so sure!

justins7 Member	# Posted: 10 Sep 2020 10:15am Reply It's amazing how much work needs to be done to avoid frost heave. rpe, where are you located? I have a few outbuildings that just rest on gravel, and they seem to just float up and down, which is maybe the way to go in some cases. For my wood posts: I am kind of doing this as an experiment. It's a wood shelter made entirely of timber from the woods, with a corrugated metal roof. I'm going to try different things, and keep some supports above ground. If the earth rejects the cinder blocks, spits them out, well, I'll just keep propping them up!

Brettny Member	# Posted: 10 Sep 2020 10:37am Reply I thought these posts arnt structural? The thing to do would be to repair the side of the building in question not prop up the other side. There are so many of these cabin stories that all start off badly with a poorly built foundation. One guy on this forum even had his cabin end up on the ground while he figured out how he was going to fix things.

rpe Member	# Posted: 10 Sep 2020 01:08pm Reply I'm in Ontario, near Sudbury. Frost heaved piers are a common issue that cottagers face in my lake system. In part it was caused by rushed construction back in the early days, when property owners were sold the land cheap, but needed to build a certain size building within a very short period of time. Adding the complication of water access, and a general lack of experience, and many buildings have ended up leaning/heaving/falling over. From your added description above, I'd proceed with caution. Did you watch that video posted earlier? It shows some examples of what happens to shallow buried supports like cinder blocks, and it's not pretty!

Brettny Member	# Posted: 10 Sep 2020 03:00pm Reply I watched that video. The power of frost is huge. Kinalberta is that you in the video?

morock Member	# Posted: 10 Sep 2020 05:24pm Reply There is another method. Prevent the frost! I use 4 inch roofing foam thatâ€™s ship lapped with skids or plywood over top. If you get good snow cover, then the frost is minimal. Depending on the height and size of your building you can also insulate to ground level. This is a little more difficult and can require a small heat source too. I get crazy frost heave, blue clay and lots of surface water.

toyota_mdt_tech Member	# Posted: 10 Sep 2020 07:47pm - Edited by: toyota_mdt_tech Reply Quoting: justins7 Thanks for all the info. toyota_mdt_tech â€” that makes total sense. I'll try the "flaring" method. And sono tube above the flair and dont pour concrete over the top of the tube, just flush or less than full. I had some typos in my first response, but cant correct them now. So glad you waded through it. Building on clay is tricky, its always moving even without freezing, its almost fluid. Good luck.

rpe Member	# Posted: 10 Sep 2020 09:54pm Reply They say that to get frost heave you need three things: 1.) Freezing soil (obvious!) 2.) Clay or other very fine particulate soil that supports ice lensing. 3.) A source of moisture/ground water from below the frost line up into the frozen area. Getting rid of any one of those eliminates the possibility of frost heave. In our area, I've heard of people insulating around their piers (like morock mentioned above), excavating around piers and replacing clay with course gravel/sand (my option), or installing sump pump(s) in holes under cottage, wired to run all winter pumping ground water out from around the vicinity of the building. That last option seemed troublesome, as the fellow I talked to that tried it said they had trouble with the water discharge line freezing up in winter. Some neighbours have tried sonotube piers below frost line with good luck, while others have still had issues. With a belled bottom below the frost line, the pier might not heave upwards, but could still be pushed sideways if ground expands more on one side than the other. That's why I excavated the clay around the pier and backfilled. It's a big job if done by hand, but has not moved in two winters so far.

Brettny Member	# Posted: 11 Sep 2020 05:20am Reply For sono tube footings there are premade ones called "big foot" basically an upside down funnel you put your tube on. There not cheap and huge so a big hole is needed.

rpe Member	# Posted: 11 Sep 2020 08:15am - Edited by: rpe Reply Those BigFoot piers look good. A similar one is called 'Footing Tube', which I think is even better, as it includes a tapered plastic column form, rather than the constant diameter sonotube. Foottube.com With either of those options, serious excavation is required, and a concrete mixer on site is probably a requirement as well given the large volume of concrete involved.

jsahara24 Member	# Posted: 11 Sep 2020 08:52am - Edited by: jsahara24 Reply I used bigfoots below my sonotubes in my Upstate NY build. I used the 28" bigfoots with 12" sonotubes. The excavation was significant, we used a mini-excavator. Our soils are sand/gravel so they tend to drain and dig well. I had a concrete truck come and pour them all in one day. They were installed around 2015 and none of them have moved at all. I put the bottoms of the bigfoots approximately 4-5' deep. My area is known for its heavy lake effect snow which tends to insulate the ground and keep it from freezing too deep, that along with the well draining soil certainly helps keep my piers stable. In retrospect, I probably could have excavated for a full foundation just as easily as we dug for the bigfoot/sonotubes, however I didn't have the skills to install a full foundation. I do wish I would have, but in reality is hasn't caused me any issues beyond a freezing shower trap when the temps get really cold.

Brettny Member	# Posted: 11 Sep 2020 09:51am Reply There is alot more dirt work needed for big foots but to say you could do a full foundation just as easy isnt correct. You need alot more dirt work, poured footings the length/ width of the building then spend days or thousands of dollars on masonry work. Just to gain square footage.

jsahara24 Member	# Posted: 11 Sep 2020 01:38pm Reply Quoting: jsahara24 I probably could have excavated for a full foundation just as easily as we dug for the bigfoot/sonotubes, Never said the full foundation was just as easy, I said the excavation would have been just as easy.... By the time I dug out for the bigfoots I was basically digging into the area of the next pier. And instead of having to dig a footing trench, I was opening up a minimum of a 36" circle and my soils kept collapsing as they are sand/gravel which tended to increase the excavation.... once they were all set and lightly backfilled, I poured them all in a few hours....Don't get me wrong, I am very satisfied with the bigfoots, I just wanted to point out you're not going to do it with a auger....

Aklogcabin Member	# Posted: 11 Sep 2020 01:47pm Reply I have that just about every cabin has its own issues. For us weâ€™re remote. Fly in in summer then 2 miles to the cabin. Winter is load everything you can get on to a snogo trailer including snogos freight sleds building materials n such. Get it up the highway full of moose n ice n snow. In the dark always. Then hook up to 800 hundred pounds or up to 2000 pounds or more of freight and go cross country to the cabin. At 20 below zero. You will break down n get stuck. And donâ€™t forget even one piece of lumber or log. No stores. So when you are out for several weeks or months, all we have is what we have. Make our own potable water n make sure thereâ€™s no accidents. My point being. I had to do what I had to do. If I wanted a cabin like I wanted. Or any cabin in Ak . North Rick n others know . But thatâ€™s just the way I love it . It was a challenge. I researched and discovered the best ways to mitigate the risks. And believe I built a fine cabin that Iâ€™m proud of. And I read about folks who are learning to build who are just as proud of their little 8â€™x12â€™ shabin. And it makes me feel good. Older folks who want a simpler life or just making it . I also suspect that very few cabins would pass Goverment codes. There are no codes here. But I donâ€™t need government to protect me from myself. I also suspect most of us would rather read positive reinforcement. Not suggesting someoneâ€™s cabin is wrong. The only person who knows all the issues to the best of their knowledge is the builder. Iâ€™ll get off my soapbox. And these comments are just my thoughts. And I do really enjoy this forum. Keep up the good work all.

justins7 Member	# Posted: 11 Sep 2020 03:25pm Reply It's really helpful and interesting to read everyone's experiences here, as always!

rpe Member	# Posted: 11 Sep 2020 05:22pm Reply For those interested, I just started a new thread with some pictures of the pier work on my workshop project. That way I don't photo-bomb Justin's thread!

smallworks Member	# Posted: 16 Sep 2020 11:06pm Reply "toyota_mdt_tech With the flare at the bottom and a sono tube, the flare keeps it from lifting out as its also frozen in, the smooth sides of the sono tube reduce the grounds ability to lift it up. This is the best option short of going below the frost line and even then, the frozen ground could still lift a post if you dont do the sono tube." We're in Northern NY,too and used sono tubes for structural integrity. So far, so good 11 years in.

KinAlberta Member	# Posted: 17 Sep 2020 01:54pm - Edited by: KinAlberta Reply Quoting: Brettny I watched that video. The power of frost is huge. Kinalberta is that you in the video? Not me. Iâ€™m way across the country. I sure do appreciate the guy for posting the video and his information as informative DIY videos on levelling cabins and outbuildings are surprisingly rare. However, Iâ€™ve posted that link before and mentioned how unsafe that situation and the method of doing the repairs seemed to be. Additionally I sure donâ€™t care for the make-do solutions used but can sure understand the issues with levelling around tilted concrete blocks. (There seems to be a need for concrete or composite wedges.) https://woodgears.ca/cottage/foundation.html

Brettny Member	# Posted: 18 Sep 2020 08:20am Reply Quoting: KinAlberta However, Iâ€™ve posted that link before and mentioned how unsafe that situation and the method of doing the repairs seemed to be That was actualy where I was going but didnt want to run someone the wrong way who clearly spent alot of time on his content. I just cant understand how he thinks that is going to be safe or even work until the following year. But I guess the only reason hes fixing it is because the shutter dosnt close. That guy actualy does pretty good finish carpentry but clearly dosnt do much framing.

KinAlberta Member	# Posted: 20 Sep 2020 08:22am - Edited by: KinAlberta Reply Heaving and tilting of blocks is one of those problems where once it has occurred its extremely hard to return to its original state. Nonetheless I think building on blocks is a quiet acceptable way to build a cabin. (Screwpiles though seem like a great option but i donâ€™t know how long they last before they rust out and fail.) Most cabins aren't meant to be full time year round homes. They are usually second homes, weekend retreats, vacation homes. Its hard to justify full foundation structures for periodic use. (Inefficient capital allocation and a waste of resources too.) However Iâ€™ve come to the conclusion that if someone is going to build on blocks they should raise the building height at its lowest point high enough to be able to get right under it to re-level it once in a while. They should also really overbuild the beams (especially beam depth) to strengthen the beams to better spread the load across problem points. Heavy duty beams will allow you to much more safely jack at one point and lift and level multiple points with far less risk of damaging the structure or flexing and weakening the beams.