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Epoxy Rebar in Slab

1LeadingEdge's picture

I am getting ready to pour an 8 inch stemwall perimeter foundation around my house in order to bump out the existing walls to the new foundation and then add a second story.  The existing foundation will not support a second floor.

Anyway part of the foundation will go through the existing garage, which has a 4 inch slab.  I am going to saw an approx 18 in wide path out the slab and pour the foundation/stemwall through the garage. 

The building department originally wanted to have the garage foundation/stemwall and slab juncture engineered but they said if I came up with a way of tying it all together they would take a look at it and I wouldn't have to hire an engineer.

The footing and stemwall will built according to what the city handout/code.  What I need is the placement of the rebar in the original slab.  I was figuring #4, epoxied into drilled holes.  But what spacing? and do I bend the pieces down and wire them to the stemwall rebar.  Or do I place the rebar in holes opposite each side of the cut and then wire them together.

Thanks in advance.

(post #94237, reply #1 of 5)

i only know what i had to do when i had a bit of underpinning to do that i can tell you.

we had to put 1/2" rebar in about every 1' vertically and bend the ends over to provide a key to key the 2 bits together.

hope this helps

(post #94237, reply #2 of 5)

The only purpose of rebar in a small stemwall is if you bumo the wall with the car. All you need is a single #5 with it pin every so often to hold in place, every two feet be fine. It does not hold any load, just impact.

The best employee you can have but you wouldn't want him as a neighbor " He the shifty type"

(post #94237, reply #3 of 5)

Hey our area all we'd require (and what I've seen from engineering doc.'s) is #4 @ apprx. 16" o/c.

Since you're not building a rocket or anything extreme (as I recently seen from a homeowner building his own observatory) which engineering required some extreme should be fine.


(post #94237, reply #4 of 5)

I'm currently working on a room addition with a similar situation.  They had an existing patio slab and the foundation contractor saw cut about 1 foot around the perimeter and drilled/epoxied #4's every 16".  They were only inserted about 4-6" and bent down into the footing almost to the bottom.

(post #94237, reply #5 of 5)


You need to tie the new footing and foundation wall into the existing structure's footing and foundation wall, so yes drill and epoxy the rebar in. The splices should have at least 2 ft overlap into the new pour.

However, there is no need to tie the garage slab to the new foundation, and in fact a strong case against doing so. In most cases slabs and foundations are isolated from each other so that if either moves, it will minimise damage to the other. There are cases where this is not so, but that doesn't appear to be the case from the info you have given.

I would cut about 3' wide through the slab (more working room) and then dig the new ftg right to code frost depth for your area. If you have, say, 16" x 8" ftg, then 3 pcs rebar should be lots. For the wall, overdo it and go with verts at 16" o/c and horizontals the same, plus one extra bar just below pour ht. Drill and epoxy all of these into existing wall and ftg.

If your inspectors make you tie the slab to the new wall then you will be buying form ply for the slab side of the wall form, as the rental guys won't appreciate holes drilled for rebar. The cost of this and epoxy (not cheap) plus extra labour for the more complicated form and numerous splices may well offset the cost of engineer - if he says no need to tie the 2 together....

How many feet of new foundation? How much of this intersecting with garage slab? What is code frost depth in your area?



Lignum est bonum.

Buccaneer Contracting

Penticton, BC