how do you tie a new foundation into an existing concrete foundation on a home addition?

Answer 1

Oh this is so much fun...You get the pleasure of boring 3/4" inch holes into the existing slab. Your luck improves as you set 5/8" rebar in the holes with a special epoxy. How I envy You!!
Someone more qualified than myself can tell you how many you require, and how far into the existing slab you have to bore.

Obviously I was a bit tongue in cheek, this is really hard, dirty work, and the epoxy gets really messy. Use a very large hammer drill. That's my best advise.

Answer 2

Don is correct.

Depending on your local building codes, they might require an engineer to design your particular application. That's the case in California, due to the earthquake hazard.

A proper design will take into consideration all the loads that your house will be expected to withstand, and specify the diameter and length, drilling depth, number and placement for the tie bars between the two foundations.

You might need 5/8", 3/4" or 7/8" threaded rods or rebar to connect them. Drilling is the easiest part: use a hammer drill - a pilot hole followed by the full-size diameter drill. Then clean out the debris and dust using a small diameter bottle-brush, followed by compressed air blown thru a tube inserted to the bottom of the hole.

The threaded rods need to be perfectly clean of oil and dirt before you epoxy them in the holes. You actually fill the hole 1/3 to 1/2 depth from the bottom with a 2-part epoxy, then insert the rod and rotate as you push it to the bottom of the hole. A 24-hour cure cycle is required for maximum strength, before you bend or reposition the rods in the new foundation.

Check with www.simpsonstrongtie.com for their earthquake tie down and retrofit bolts and epoxy system for more information. www.hilti.com is another supplier.

Answer 3

One way is drill in anchor bolts. Redhead brand is the only one I know of. Go to home depot or lowes and ask someone in building materials or hardware.