I am currently extending my existing concrete garage base as i have bought a larger garage.
Does anyone have any tips on the best way of tying in the old base to the new.
I am extending the rear of the base by 18 inches and as the back of the existing base is 2 feet above ground, and will take the full weight of the rear of the garage i am concerned that if i do not tie them together proprerly then over time the new may break away from the old.
You definately can't wing this...You need an engineer's assistance. The old slab will typically tie to the new with a lot of rebar dowels drilled and epoxied into the old slab and into the reinforcement grid of the new slab.
If the slab is bearing the new exterior walls, you'll need an adequate footing design to support the slab as well.
In a nutshell, you can't get this designed for you online.
I use a hammer drill and a 1/2 x 18 drill and drill horizontal into the existing concrete. Then I pound in 1/2 in rebar. I would use footers on the end which is pretty much a requirement in most areas.
Here is a picture.
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