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Discussion Starter #1
Seems there are differing opinions?

A new slab will be formed up against an old stem wall. Should I dowell it in (maybe #4 rebar?) or use some sort of expansion joint?

What's the best practice?
Thanks!
 

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remodeling pro
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Seems there are differing opinions?

A new slab will be formed up against an old stem wall. Should I dowell it in (maybe #4 rebar?) or use some sort of expansion joint?

What's the best practice?
Thanks!
I would use a rubber or pvc expansion joint, but would definately dowel them together for vertical movement.. What is your area of the country? These type of connections are notorious for moisture problems in areas with high water tables. Is there going to be a wall framed at this joint? If so, be sure to get professional insect treatment; these hidden joints are like sounding the dinner bell for termites.
 

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Discussion Starter #4
Thanks for the response.
I'm in the high desert, eastern CA. Water table is high but we have super low humidity so things dry out quick. Termites aren't much of an issue around here (too dry?). Maybe I'll treat the joint anyway for peace of mind.
For some reason I was thinking one or the other, but an expansion joint with dowels makes sense.
 

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Discussion Starter #5
Another question...
The porch will have 2 post footings and will also be doweled into a large chunk of concrete (previous base of steps).

Should the post footings have an isolation joint?

If so, is there an easy way to do that with a single pour?
Maybe sonotubes with isolation joint around it?

Just trying to minimize cracks!
 

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Civil Engineer
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If the porch footing is done properly, there is no reason to attach the porch foundation to the house. If the house is moving vertically, you have big issues, and doweling the porch into the house is not going to solve them. If the house is not moving, and the porch is, doweling is going to break the concrete at the joint. If the house is not moving, and the porch is not moving (that is how it should be), then doweling accomplishes nothing, and is a waste of time and money.
 

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Me three with a "no" to doweling. Doweling only should be applied where structural connections are required for load distributions. In your case, a simple porch should be allowed to move independent as there is no structural loads that need to be distributed to the foundation.

FYI Queso and Trouble...if you dowel a joint then an expansion joint filler is a waste as the dowels will prohibit the parts from expanding or contracting.
 

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Disimilar methods of construction never get doweled together. (Frost protected don't get doweled to non-frost protected, or slab on grade)
 

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Disimilar methods of construction never get doweled together. (Frost protected don't get doweled to non-frost protected, or slabs on grade)
Correction: remove red and add blue

Slabs on grade do get doweled to foundations in certain situations but when the "disimilar" factor is frost protection, then no dowels should exist as something will eventually crack in the assembly.
 

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Discussion Starter #11
hmmm...
I was all content with no dowels, but now I have my inspector saying he would dowel (but it's up to me) and the concrete finisher says he always dowels.
So we're at about half yes, half no. Guess it doesn't really matter as long as the subgrade is prepped well?
 
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