Decks, Patios, Porches and Docks - deck slanting

The deck on the home i judt bought is slanting towards the house. I mean REALLY slanting. What is going on? Someone said something about a frost line. What does that mean and how do I fix it?
Please help.
Thanks :wall:

The frost can raise the supports for your posts.

Under some conditions the frost will heave an object up and then let it settle. Under other conditions, it can raise and object and it will remain higher than before. The same thing can happen again every year. This is the reason rock or stones can be raised to the suface of the ground every spring.

If your posts or post supports are not below the frost line, they can heave upward. Even roughly dug concrete posts can be raised because of the rough sides.

The best foundations for a deck are those that are dug with a slighly larger (wider) portion below frost and a sonotube (cardboard) form inserted to the frost level and filled with concrete. The area between the tube and the undisturbed soil is then refilled. The bulb at the bottom and the smooth sides of the tube prevent heaving.

In your case, you could support the deck and cut the posts providing you have a concrete pier in the ground.

Dick

luvmy03marine,

Where are you at?

Like Concretemasonry suggested, it sure sounds like frost heave has lifted the footings of the deck. The only solution is new footings, done properly, as Concretemasonry described.

If your posts or post supports are not below the frost line, they can heave upward. Even roughly dug concrete posts can be raised because of the rough sides.


Hmmm... the contractor who poured the footings for my deck used an auger to dig the hole (14" diameter, 42" below grade, to code), and filled the hole with concrete but only used a small length of sonotube at the top to form a nice round pier.

What are the chances that I'm going to have frost heave problems? I live in Northern Illinois. The soil is clay.

There's a pretty good chance you'll get some heave.

He SHOULD have filled the bottom 12" to 15" of the hole with concrete, THEN used the sonotube to get above grade.

Michigan. How do I know where the frostline is?

Probably 42", but go ask at your local bldg. dept. to be sure.

There's a pretty good chance you'll get some heave.


Ugh, I hope not. I would have wasted $8000 and a summer's worth of work. It's a low deck so there's no chance of replacing the piers without destroying the deck.

On the plus side, this site has good drainage with a substantial slope away from the house under the deck, which gets much steeper past that. The previous deck that this new one has replaced didn't show obvious signs of frost heave. In fact, the posts (buried in concrete piers) kinda sank over time instead of being heaved up, which is why I replaced the whole thing. So... I'll keep my fingers crossed and hope for the best.


He SHOULD have filled the bottom 12" to 15" of the hole with concrete, THEN used the sonotube to get above grade.

Yep. :( I wish I had picked another contractor, but I really didn't know better at the time.

One thing about frost heaving -

The soil type can have as much effect as anything.

Sand and well drained soil have a minimum potential of heaving.

Clayey and silty soils can heave much more because of the moisture content.

Layered soils can heave much more than either due to the possibility of "frost lenses" that collect water and prevent drainage.

I bought a home in northern Michigan (48" or so frost depth, water table at 7') that had a front porch/deck (6 x 12) supported on 12 x 16 concrete slabs 4" thick that were at ground level.

There was no heaving for the 9 years I lived there. - Probably due to the sugar sand that drained well.

Not all sites are the same.

Dick

I talked with our village building inspector about frost heave with concrete piers and no tube vs. tube. There seems to be two schools of thought on this issue. One school of thought is already presented here in this thread which advocates using the tube nearly all the way down.

Conversely, my building inspector advises that filling the hole with concrete without using a tube is actually a good thing. The reasoning he put forth was:

1) The rough surface of the hole is actually beneficial in retaining the concrete pier in the ground, as opposed to helping to push it out.

2) Using a tube all the way down can actually result in more frost heave problems since the paper/fiber former wicks water down the sides of the buried pier. The paper will eventually decompose but that will still leave a gap which lets water in and surround the buried pier.

3) The backfill around the tube, not being as compact as undisturbed earth, will allow more water to seep down and around the pier than undisturbed earth. Also, filling a hole with concrete without a tube will result in a more stable pier since backfilling is not required.

I'm not necessarily advocating either position, just presenting the ideas. However, our inspector hasn't seen any frost heaving problems with piers poured in our area using the no-tube method, and that's the important thing to me.

I have not had a problem using tubes on anything i've done. Ask your inspector how many years it will take for the tubes to rot, its waxed cardboard, wont happen all too fast.

Now onto the rough hole vs using a tube. Take a piece of smooth 3/4 EMT pipe, put it into a vice and try to pull it out. You wont have any grip. Try the same thing with 3/4" all thread. You will be able to grip the all thread. Thats the same way i look at using a tube vs not. Frost kind of works like a wine bottle cork, it slowly pushes things up. If it has something it can "grasp" it will go quicker.

Now, as lefty suggests (and i also do) don't use the form all the way down. A bell shape to the bottom of the concrete will stop frost from being able to heave the concrete out. This is assuming you used the proper depth hole to start.

We can argue the 2 different syles forever and it's not going to change anybody's mind. I don't deal with frost more than once every year or so, but I know the footing the inspectors in those areas are looking for -- what they will pass and what they won't.

The 2 that they will pass are a "tee" and a "cone".

The "tee" is like I described initially -- a hole at the proper depth, 12" to 15" of concrete in the bottom, then sonotube to the top and about 6" above, with a CB or PB set in the top of the wet concrete.

The "cone" has a narrow opening at the surface and the sides taper out to the required width near the bottom of the hole. Too time consuming for me to have the crew dig them that way, so it's sonotubes for me.

What they won't pass is a 16" to 18" hole that has straight sides from top to bottom that is then filled with concrete. (This ONLY applies in the few areas I work in where frost is an issue.) Their reason is that frost can heave THAT footing by forcing the frozen soil against the sides, leaving it only one way to go -- UP!