Adding support to a cantilever

[SouthernTier]

Before I get to starting my cabin (next year for sure!), I should fix up a few things around my house in town.

A former owner expanded the dining room by cantilevering it about 4' out past the foundation.  They didn't do a very god joob, especially since part of the cantilever was over a window which didn't provide good support, and other problems.  As a result, we have cracked walls and ceiling.

I want to go ahead and support this.  I plan to install two sonotubes with good footing.  Since I won't be able to get under the cantilever, I will have to drill these right next to the corners of the overhang, and then use a spade to scrape off the soil under the cantilever and pull that out with a post hole digger.  So after a lot of work, I should have an oval shaped hole into which I will install the sonotube such that it is under the overhang.

I will add a new exterior beam under the overhang to distibute the support from the two new posts at the corners (note, the overhand is about 10' - 12' wide or so.

My question is this: ideally I would actually push the overhang up a few millimeters or whatever I can get because (as evidenced by the cracks in the ceiling) it has sunk some.  Any suggestions on how to push it up before I install the 6x6 posts from the sonotubes to the beam?  I was thinking of using a car jack pushing against another 6x6 post, but I have nothing to put on the other side of the jack - it will just sink into the ground rather than push the overhang up.  I suppose I could double the sonotubes so I have one for the permanent post and one for the jack, but that seems like a lot of work for something that may not even work.

Any suggestions on my approach and/or my question?

[MountainDon]

It would help visualize this if there was a photo or two.   The cantilever protrudes 4 feet... 10-12 feet wide.   Probably too much to span with only 2 posts.   What about carrying the weight to the ground... needs a foundation to spread the weight out.  What is the existing foundation?  Single story?  Load bearing wall?  How did they fit the joists for that?    Ground frost depth?  .....

[SouthernTier]

I can get some pictures later, but here is some more info:

• It is true that two posts would not be enough to support a 4' overhang, 10-12 wide by themselves.  I am mainly interested in making sure that it doesn't droop any further.  In other words, I just want to fix the cracks in the ceiling (walls aren't as bad) and not have to worry about having to do it again in a couple years.
• Same thing about the foundation - I will need to have a good area below the sonotubes to spread out the weight.  Still working on that.  But again, these are just to stop further drooping, not to provide full 100% support.  I agree, designing for full 100% support would need something must more involved, preferably a whole new block wall with footers at frost depth.
• Existing foundation is a full basement concrete block foundation in good shape.
• What the former owner did was to cut out the rim joist where the extension was going.  Then he sistered in joists to the existing floor joists which were running in the same direction.  However, he only overlapped those joists about 5-6 feet (say, perhaps used a 10' board, with 6' inside and 4' outside) and probably didn't have enough nails so it is drooping down some past the foundation wall.  Also, as I mentioned, part of the overhang extends over a window, so there wasn't much supporting the board laying flat on the top row of the concrete blocks, so it drops a bit there, too.
• The house is a ranch, so no load bearing walls in any of these sections.  The retrofit of the roof was just a separate shed roof at a shallower angle so it reached out to the new end of the room.
• In general, we design for a 4' frost depth around here.  I am fortunate, however, to have my house in an outwash area so rather than the glacial till that is mostly around here (and heaves a lot), the soil is much more granular and less susceptible to heaving

[Don_P]

If I'm understanding right the original roof is bearing on the wall above the block basement wall with the window in it. If so it is a load bearing wall. Then the cantilevered addition has a shed roof that is bearing on the wall out at the end of the cantilever, 4' out beyond the basement wall. This is also a load bearing wall. If that is correct, you have half of the 4' cantilever plus the roof overhang bearing on the proposed beam, half of the 4' floor depth. Will the piers be at the ends of the bumpout or inset from the ends... is the beam span 12' or something less with overhanging ends?
Work out the loads and see what it would take for a beam. I'm not at all sure you can't do it on 2 piers.

[DaveOrr]

The jacking up is the easy part.
Drop 2 patio stones underneath the overhang so you can jack up on the overhang.
I would go in about 3 feet from each end.
Use a pair of 15-20 ton bottle jacks on the patio stones to jack up on the frame of the overhang.
Be sure to use a block of wood between the head of the jack and bottom of the frame.
If the overhang is high enough you can use a piece of 8X8 a foot or so long in place of the patio stones.
I used this system to raise the floor of my addition that was sinking and it worked great.

http://www.homedepot.com/p/Big-Red-20-Ton-Low-Profile-Bottle-Jack-T92007A/100595081?N=5yc1vZc8mp

[SouthernTier]

Thanks all for the suggestions.  I have photos.

Here are three shots of the overhang from the outdoors:





(yeah, I am going to fix that siding, probably be removing the battens and adding cedar shingles like the rest of the house!)



The problem appears to be too short of boards sistered into the joists, and insufficient nails.  You can't see from these inside photos, but there aren't a lot of nails, and the inside ends are about 1/4" up from being flush with the joists.



But the biggest problem is that some of the cantilevered joists are resting on a mudsill that is over a window.  There is no real support under this portion of the mudsill.  To make matters worse, the mudsill isn't even continuous - there is a break for a new board over the window.



Here are some pictures of the cracks:

This is the wall on the non-window end:



And on the window end, where there is more "drooping":





The crack is about 1/8" in width at the window end.  At the other side, there isn't really a crack, but there it is clear where the overhang starts.

[SouthernTier]

If I'm understanding right the original roof is bearing on the wall above the block basement wall with the window in it. If so it is a load bearing wall. Then the cantilevered addition has a shed roof that is bearing on the wall out at the end of the cantilever, 4' out beyond the basement wall. This is also a load bearing wall. If that is correct, you have half of the 4' cantilever plus the roof overhang bearing on the proposed beam, half of the 4' floor depth. Will the piers be at the ends of the bumpout or inset from the ends... is the beam span 12' or something less with overhanging ends?
Work out the loads and see what it would take for a beam. I'm not at all sure you can't do it on 2 piers.

Don:  As usual, you are correct.  I realized soon after I typed that they are load bearing walls.  It was a quick note after the original lunch time post.

If I read your evaluation correctly, you are assuming that no credit could be assigned to the cantilever for the support.  In that case, I see how the piers would have to support half the bumpout and half the shed roof load.  However, this is how I was looking at it:

I have been living in this house for 25 years.  It was only after I bought my country property 9 years ago and started thinking about building a cabin did I start educating myself about building design.  Of course then I started seeing deficiencies in my house that I hadn't noticed before.

But over those 25 years, the cantilever has worked "good enough" to create at most an 1/8" crack.  Now, that means it *didn't" work, at least not correctly (you'd think some sort of light would have gone in their head when they cantilevered over that discontinuous mudsill over a window, but whatever).  However, the "good enough" part means that the cantilever is providing some amount of support for the entire bump out.  If it weren't, I'd expect to have had some catastrophic failure by now, especially after this past winter here in Buffalo.  For example, here is a video I took on the other side of the house after the November storms last fall:

https://www.youtube.com/watch?v=6No6Z4Qyt9Y

My thinking was that even though the cantilever doesn't provide quite enough support, it provides quite a bit.  I'd only have to install the piers to keep the addition from sinking any further, not fully support half the addition and half the roof.  That way I could repair and repaint the ceiling and not be looking at doing it again in 5 years.

Or is that wishful thinking?