Deck expansion - how to stabilize new posts?

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  #1  
Old 06-15-04, 01:04 PM
Gibber
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Deck expansion - how to stabilize new posts?

Hi all,

First off, I'm a new home owner - and hence a new DIYer for these types of projects. I'm also located in Southern Ontario, Canada - just for the record.

My house is a raised bungalow design, and as such has a deck off of the back door about 8 feet off the ground (deck is about 10'x15' in size). The deck has not been treated very well, but is stable and reasonably well built. However, the support posts are all free standing - and by that I mean, they are not only not sunk and concreted in the ground, they are actually currently just sitting on a bed of gravel. However, they have been standing that way for 17 years... so it seems to have worked whether it is proper or not. I also don't know if they were done that way for a reason or not. I've noticed a *large* amount of heaving in anything that *is* sunk in the ground.

In any case, my question is that we would like to build a new section to the deck, lower down (about 4' off the ground). I would assume that one end would normally use the same support posts as the existing deck, but then how should the other posts be mounted? I'd think that only sinking some of the posts would be a bad idea? Should I instead make the whole new section free standing - or would that cause even worse problems? Or should I just follow the convensions of the existing section?

Any advice would be greatly appreciated!

Thanks,
Gibber
 
  #2  
Old 06-15-04, 10:48 PM
L
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Location: Arlington, WA
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Gibber,

Welcome to DoItYourself.com and the deck forum.

Obviously, whoever built the deck didn't follow conventional wisdom in constructing the deck. They probably learned just how deep the frost line is where you live, and the thought of digging holes that deep scared them off.

Done properly, (or at least done so as to conform to conventional wisdom and building codes), your footings need to be sized according to the load that they will be carrying, and set deep enough so that the bottom of them is 6" below the frost line. (ANYTHING that is dug into the ground that doesn't extend below the frost line is going to heave.)

So, you need to first ask the local bldg. dept. how deep they consider the frost line to be. You holes need to be 6" deeper. Then, ask how big do the footings need to be. It will depend on how far they will be spaced, which is determined by how large your beams and joist are, and how far they are spaced (plus whatever snow and wind loads you have to meet).

If they tell you that you would need 18" footings and the frost line is 42" (1/2 meter cubes and the frost line is about 1-1/4 meters deep) then you dig holes that are 1-1/3 meters deep (4'), fill the bottom 18" (1/2 meter) with concrete, set a 6" or 8" Sonotube on the center of it and backfill around the outside of the Sonotube, then fill it with concrete -- (all of this is done in pretty much one pour so that the concrete is continuous) -- then set a post base in the wet concrete a couple of inches higher than grade. Those footings won't heave.

Just because the original builder didn't do it right (and got lucky that it never heaved!!) doesn't mean that you should follow in his footprints.
 
  #3  
Old 06-16-04, 05:58 AM
Gibber
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Thanks Lefty!

That all sounds like good advice. Does that mean you would suggest building the add on deck properly, with proper footings? If so, should I be worried about the connection to the existing deck (since one may move (heave) differently then the other). The best answer, I would guess, would be to rebuild the supports on the existing deck, but that is more work then I'd really like to do right now.

Thanks again, all your work here is really appreciated!
Cheers,
Gibber
 
  #4  
Old 06-16-04, 07:57 AM
L
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Yes, I would build the addition to the deck with proper footings. And I would make it free-standing from the existing, other than any stairs that might connect one to the other.

As for the existing deck, it "should" have its posts set on proper footings, but last sentence leads me to believe that's not going to happen, at least for a while. Since it's been like this for 17 years or so, I probably wouldn't mess with it either. I would figure that the existing deck is going to be replaced in a few years, and the problem will be corrected then.
 
 

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