Foundation support for a masonry chimney chase

[Jeff Beck]

Is it permissible to support a masonry chimney chase with a 24" poured concrete foundation that's attached to the house foundation with rebar?

The location is Chicago and the frost line is 45".

I don't have any pictures, a sewer contractor that's working on my daughter's house called me today and said that he had never seen anything like this before. There are no wing walls or a 45 degree wall that rests on the footing.

The chase is approximately 24' high and 48" wide.

Jeff

[mgbinspect]

Not enough info there, Jeff. If you don't have photos, you must paint a pretty crystal clear picture so we can at least visualize your area concern.

[Jeff Beck]

Thanks Mike,

I was hoping to get lucky and find someone who had seen something like this before. I was able to get to the site early today and have taken some pictures.

Here are some establishing shots:

Split face masonry chimney chase:

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Lower portion of the chase:

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Exposed lower portion of the chase:

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The foundation for the house goes down another 24" below grade. Every masonry chimney chase that I've seen is supported by either wing walls or a bump out pocket in the foundation so that the load of the chimney is carried down to the spread footings. Occasionally, I'll see support walls that cut back to the foundation at a 45 degree angle. I have never seen anything like this before.

As I said in my original post, the frost line in Chicago is 45". The base of this chase terminated well above the frost line. My concern is that there may not be enough of a base to carry the load of the chase and secondly because of the depth to counteract frost heave.

This builder has taken numerous short cuts (as evidenced by the washed-out sewer line in a 3 year old house) so I am being overly suspicious of anything I find.

I'd really appreciate any comments if this is suspect and if so where I might go to find a code reference (if one exists) or if I'm making a mountain out of a mole hill.

Thanks,

Jeff

[Tom Raymond]

Well, it is a mountain now that it's been undermined.

Edit: If the place is only 3 years old the plans should be on file. Sounds like you might want to go get a copy of them.

[mgbinspect]

Well, I'm not an engineer, but if the concrete shelf is original work poured into the concrete foundation, which it appears to be, I wouldn't be too concerned. The photo you posted scales approximately 36" of vertical steel reinforced concrete before transitioning to the masonry chase. That's pretty substantial. Then the work above is tied together through the interlocking nature of masonry, so the entire support has to fail, before it becomes a serious event. Do keep in mind it's not a solid masonry chimney, which would be considerably heavier. It's merely a masonry chase, which is still heavy. It's pretty difficult to imagine a failure based upon those photos.

Also, keep in mind that a spread concrete footing is important when the soil is the reciever of the weight above, but that does not appear to be the case here.

[Marc]

Given the financial consequences of a failure of any type involving that chase, I'd immediately punt to an engineer and get that burden off of my shoulders.

Marc