I live in Carrollton, TX. My house is a float slab concrete foundation which means no piers under the slab foundation to support the foundation. This is how TX builders build house. I want to add another 850 Sf. The new foundation will ties into the old foundation. I want the new foundation has piers support the foundation.

One contractor told me I can build the addition foundation with the piers support. However, another contractor told me I could not because when the foundation movement may give me a problem later since the old foundation did not have any support so it can move freely which will create crack between the new foundation (has piers) and old foundation.

Who is right? What option do I have? I hate to have the new foundation without piers support below the foundation.

Thanks

The two foundations should be built the same if you want them to float the same. In most cases they will not mechanically attach one to the other since this will be a flex point no mater what they do to join them. You will need to consider your flooring material that will be covring the area where the two foundations meet. Carpet would hide and flex the best while ceramic tile would surely crack and show broken grout seams, eventually.

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