Poured Foundation Options

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  #1  
Old 12-13-16, 10:21 AM
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Poured Foundation Options

I'm currently working with my builder on finalizing the design of my garage addition, and we've hit a snag with respect to the back wall of the garage. I would like the back wall to fall just about at the center of the chimney, but apparently this is a problem. He said tying the new foundation into the foundation where the chimney rests is not a good idea. I've gone through multiple iterations of my drawings and the middle of the chimney is the best for my design for more than one reason. What are my options foundation-wise for achieving what I want? For example, perhaps a single footer can be poured near the chimney to pick up the load of the garage back wall on the left side? Or would the soil in that area apply too much force to the chimney foundation? BTW, the chimney foundation is the same thickness as the house foundation (it's one continuous pour 7 feet below grade), but I believe the area under the chimney is void because it's an ash dump. I'm thinking there has to be some way.

Wall on the right side is a 12 ft balloon wall, 2x4 studs. Foundation is 12" wide and 7' below grade with finished basement.

And here is a floor plan view of the proposed design, only I want the back wall of the garage/front wall of mud room to meet at the center of the chimney.

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The issue with having the back wall of the garage even with the back of the chimney is the roof lines get all screwed up. It causes the roof to interfere with my forward-most skylight and creates a trough against the front of the chimney. And bringing the back wall to the front of the chimney makes my garage too small. The middle is perfect. Unless there is an alternate way to do the roof. Like maybe a hip roof on the back.
 

Last edited by PJmax; 12-21-18 at 09:33 PM. Reason: removed picture
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Old 12-13-16, 11:18 AM
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Seems like digging down to the existing footing and pouring a new footing to pick up the load from the left rear half of the garage would be a viable option. That way it is not exerting any lateral pressure on the existing foundation.
 
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Old 12-13-16, 11:21 AM
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Hi mossman,
I'm not a pro at this, but why would meeting at the middle of the chimney be any different from the back wall of the mud room meeting in the middle of the dinning room. I'm not sure what he is anticipating for a problem but IMO, certainly can be done. Even if he had to dig down to the level of the footing under the chimney to provide support to that end, it sounds like that would be much better than the other problems you describe. The pros will be along.

Bud

LOL, good thought, you beat me to it.
 

Last edited by Bud9051; 12-13-16 at 11:22 AM. Reason: addition,
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Old 12-13-16, 11:49 AM
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Rather than a pier, it seems to me that the entire back wall could be poured down to the depth of the existing footing so it is one continuous pour. We're only talking about a 10' wide wall, so a little more excavation and a little more concrete. So what. And the remaining foundation walls (mudroom, right front and left of garage) will be 24" deep as originally planned.
 
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Old 12-13-16, 02:21 PM
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it seems to me that the entire back wall could be poured down to the depth of the existing footing so it is one continuous pour. We're only talking about a 10' wide wall, so a little more excavation and a little more concrete. So what.
Here's what I think the concern is. The builder wants the wall tied into the existing foundation wall, not the chimney.
The chimney foundation is a protrusion of the foundation, and extending off of that just adds more weight to a small (narrow) foundation.
Their concern might be that it would settle or heave over time.
 
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Old 12-13-16, 02:35 PM
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Here's what I think the concern is. The builder wants the wall tied into the existing foundation wall, not the chimney.
The chimney foundation is a protrusion of the foundation, and extending off of that just adds more weight to a small (narrow) foundation.
Their concern might be that it would settle or heave over time.
Yes, I believe that is the reason. His plan is for the footings to be 24" deep. However, if we dig down to the existing footer and pour the new wall, there wouldn't be a need to tie into the existing foundation, correct?
 
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Old 12-13-16, 03:14 PM
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My understanding is that a foundation needs to move as one unit.
Whether the tied-in foundation is 24" deep or 7', it still needs to be secured with rebar to the long foundation wall, not the short. This is so the new wall can't move up and down.
 
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Old 12-14-16, 07:52 AM
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My understanding is that a foundation needs to move as one unit.
Whether the tied-in foundation is 24" deep or 7', it still needs to be secured with rebar to the long foundation wall, not the short. This is so the new wall can't move up and down.
Okay, but excavating down to the existing footing and tying the new foundation the entire depth of the existing foundation wall would be better than 24" deep and tying in a depth of only 24" correct? I suppose it isn't a good idea and I'll have to explore other options to make the roof work.

Maybe I could bring the foundation to the front of the chimney then pick up the trusses with a beam that spans the width of the garage. The mud room roof would then reach back over the garage to the front of the chimney. This would make my ceiling lower than I wanted in the back 6' of the garage, but I guess that wouldn't be such a bad thing.
 
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Old 12-14-16, 08:30 AM
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If the entire foundation were being poured new, what would they be doing different from what you are suggesting with the full wall along the back? The only difference I can think of would be the footing would be continuous, but a proper footing isn't going to move, either the existing one or the new one. Plus the walls will be tied together.

Don't give up so easily. If necessary have an engineer specify what needs to be done to make it secure. My bet is he would approve what you have proposed.

Bud
 
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Old 12-14-16, 08:39 AM
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If the entire foundation were being poured new, what would they be doing different from what you are suggesting with the full wall along the back? The only difference I can think of would be the footing would be continuous, but a proper footing isn't going to move, either the existing one or the new one. Plus the walls will be tied together. Don't give up so easily. If necessary have an engineer specify what needs to be done to make it secure. My bet is he would approve what you have proposed.

Bud
Exactly my thoughts. Things shouldn't be moving at all. The footings themselves can be tied together as well. I'm going to keep pushing it. There is some uncertainty on his end, so we'll have to see what his engineer says.
 
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Old 12-14-16, 08:51 AM
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Bottom line is not whether it can be done but how to do it. Tell him the wife wants it your way and he will know that is the way it has to be .

Bud
 
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Old 12-16-16, 12:09 PM
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I think I found a better solution--adjust the roof pitch to that of the covered porch. This will allow me to keep the back wall at the rear of the chimney like the builder wants, and will solve the issue with the chimney roof line. Even more, it will look better from the front because the garage roof will line up exactly with the covered porch, whereas before it was piggybacked for a few feet which looked like crap.
 
 

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