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Frost Heaving Fix For Deck Posts

Ann_Berg's picture

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When put an 8'x12' deck on our cabin in NW Wisconsin, some of the locals warned us not to put a ledger board on the cabin - just asking for trouble, they said, with frost heaving. But, of course, we thought we knew better, and figured if we did a bang-up job on the posts, we wouldn't have any frost heaving to speak of. We followed directions METICULOUSLY, using 4' long cardboard tubes with an additional space for a "concrete foot" on the bottom. We were proud of our efforts, because some of the DIY's idea of a footing in our area involves a 5 gallon bucket and two bags of Quickrete! Anyway, we filled the 4' cardboard tubes with concrete, added 5"x6"posts on top of that, and built the deck on top of the posts, and for a few years, we were just fine. This winter, however, the deck has heaved noticably! The side farthest from the cabin has heaved about 1to 2 inches up, whereas when we built the deck, it sloped about 1/2 the other direction (away from the cabin). I know the heaving will subside somewhat in the spring, but what should we do then? By the way, one of the problems might be related to our water table, which is very high, and our soil, which is heavy clay. Any suggestions short of a hand grenade? Another disheartening thing is that our neighbor's deck, which he constructed WITHOUT cardboard tubes for his footings (he told us those tubes were a waste of time and money), and who didn't put his footings as deep as ours, hasn't moved a hair!!! Is this related to Murphy's Laws for building, or does he know something we don't know? And what about the two decks we're going to build this summer on the front of the cabin? To ledger board, or not to ledger board, that is another question! Even more important, how do we prevent frost heaving on the footings to be constructed in the front of the cabin as support for the two new decks? We are a Zone 3 where it gets as cold as -20 to a -40 (although we have a good snow cover, even this winter, which has gone on FOREVER.) Ideas and thoughts are welcomed and appreciated!

(post #159355, reply #1 of 11)

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Does the cabin have a proper foundation?

(post #159355, reply #2 of 11)

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The question about the foundation is a good one. It has a crawl space about 5 blocks high, and painted with waterproofing material that does appear to work very well, with presumably good footings underneath that, but it has a dirt floor. We heat the cabin all winter, so the crawl space never freezes. We didn't build the cabin; we bought it as a "shell", and after 10 years, it does have some hairline cracks following the block foundation in the exterior corners of the foundation. However, there isn't movement in the cabin in terms of walls and floors, and such. I should also mention that the deck is really a bit "twisted", as there's more heaving at the end of the deck where the stairs are located than at the back. I hadn't thought about that until just now, but it's possible the stairs are the culprit, and it just appears to us that the posts have done the job! Do you think that's possible?

(post #159355, reply #3 of 11)

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I will most likely will catch heat for this one but who cares. I don't like sonotube, I believe like your neibor they are a waste of money and not as good of a job. Hear me out. When you dig a hole in virgin soil and fill the hole with cement, unlike sonotube then back filling, your soil is naturally compacted against the virgin soil and less likely to move. Though this may not be your problem, water table clay and murphy's law could be the route of evil here.

(post #159355, reply #4 of 11)

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I know our frost line is 4', so I dig my deck piles 6'. All my decks seem to have faired okay (hmm...maybe I should take a drive and check that). Wet clay has a nasty habit of adhering to the piling, and is capable of pulling it up when it freezes. In this case depth of the pile really wouldn't make a difference. If the locals aren't using a ledger and they don't have your problem, I wouldn't use a ledger either.

(post #159355, reply #5 of 11)

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Ann, Your problem of course, is not whether to use a ledger board or not, but how to keep the posts from frost heaving. It's possible that the ground froze deeper than your footings, if the weather conditions were right. It certainly was cold enough in Northern Wisconsin to do that this year. It's also possible that because of site conditions,(moisture, ground cover, snow cover , soil type, exposure etc.), that your neighbors' footing did not freeze. Frozen clay soil can definitely grab onto a post as it heaves. A common way to prevent this is to fill around the post with pea gravel. You could also try scattering some ground cover around the base area of the posts in the fall...(straw, hay, sawdust, landscape bark shavings etc. to insulate around the posts a bit) In my opinion, your installation method is the correct way to do it. Your deck posts will last much longer that way. If you do this again, I would dig them deeper and fill around them with gravel. Good Luck!

(post #159355, reply #6 of 11)

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I always put a piece of visqueen or a heavyduty garbage bag around the sonotube before I backfill.Seems to help. Good Luck, Dave

(post #159355, reply #7 of 11)

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David is right on the money. 'Bearing' piles to prevent the structure being affected by frost heave should be isolated from the ground that heaves otherwise they will just lift with the ground.

(post #159355, reply #8 of 11)

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The concrete cloumn with footing below frost seems good if correctly reinforced with rebar. Wrapping with plastic not useful here in Alaska where I have been building since '58. For best results we make concrete piers in an inverted funnel shape which is 24" at the bottom and tapers to 12" in the first foot and to 8" in the next 3'. Above that our forms are made to take extensions of 8" stovepipe or sonotube. 3 or 4 vertical rebar 2" from outside wrapped every 10" horizontally with smaller bar (we use crab rings) and a good mat 2" from bottom tied into a circumference ring and the verticals works in our silty clay soils when placed 10'-12'on center for average loading. The bearing capacity of the soil is determinate and without site engineering we rely on the US Soil Survey. However, you should follow up on the idea of the stair causing heave. If you can see a gap between concrete and post, or post and deck framimg members near the stair then change the stair attachment. We often just attach a stair to a deck with strap hinges so that it may pivot with heaving and thawing if heaving is not too great. Otherwise, you may also want the bottom of the stair on a footing below frost. Small cabin solutions can be as simple as a truck jack and a few pieces of scrap for shims.

(post #159355, reply #9 of 11)

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Old Bull, I'm sorry buddy but I also live in AK. and the visqueen works just fine for me.Do you really do all that stuff for every deck or just the T&M jobs : ) I do agree with the hinges on the stairs, I do that to all my decks w/ stairs that just sit on the ground.Dave

(post #159355, reply #10 of 11)

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Ann if it were me I wouldn't do anything until I see what happens in the Spring. Possible repairs range from completely rebuilding the deck, without the ledger board, to merely truing it up where it is and moving on with life.

If you do choose to rebuild the thing getting rid of the ledger board is a good thing. I seldom use a ledger board choosing instead to let the deck float on its' own. Especially in unstable soils that seems to work the best.

As for just how to fight the frost heave; that will depend on your specific soil conditions. The visqueen on the outside of the piling is a common trick. BUT, it must be a Double Layer. That guarantees the soil won't grab the post. I've seen single wrap visqueen heave but have never seen a double wrap heave. That trick can be used in other unstable soils too.

(post #159355, reply #11 of 11)

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When put an 8'x12' deck on our cabin in NW Wisconsin, some of the locals warned us not to put a ledger board on the cabin - just asking for trouble, they said, with frost heaving. But, of course, we thought we knew better, and figured if we did a bang-up job on the posts, we wouldn't have any frost heaving to speak of. We followed directions METICULOUSLY, using 4' long cardboard tubes with an additional space for a "concrete foot" on the bottom. We were proud of our efforts, because some of the DIY's idea of a footing in our area involves a 5 gallon bucket and two bags of Quickrete! Anyway, we filled the 4' cardboard tubes with concrete, added 5"x6"posts on top of that, and built the deck on top of the posts, and for a few years, we were just fine. This winter, however, the deck has heaved noticably! The side farthest from the cabin has heaved about 1to 2 inches up, whereas when we built the deck, it sloped about 1/2 the other direction (away from the cabin). I know the heaving will subside somewhat in the spring, but what should we do then? By the way, one of the problems might be related to our water table, which is very high, and our soil, which is heavy clay. Any suggestions short of a hand grenade? Another disheartening thing is that our neighbor's deck, which he constructed WITHOUT cardboard tubes for his footings (he told us those tubes were a waste of time and money), and who didn't put his footings as deep as ours, hasn't moved a hair!!! Is this related to Murphy's Laws for building, or does he know something we don't know? And what about the two decks we're going to build this summer on the front of the cabin? To ledger board, or not to ledger board, that is another question! Even more important, how do we prevent frost heaving on the footings to be constructed in the front of the cabin as support for the two new decks? We are a Zone 3 where it gets as cold as -20 to a -40 (although we have a good snow cover, even this winter, which has gone on FOREVER.) Ideas and thoughts are welcomed and appreciated!