Foundation add-on

[rlskfoster]

Does anyone know what the downside of adding on to a post-tension foundation would be, other than covering some of the ends. A friend is thinking of building an addition on to his house and he was curious if their are any associated problems. I figured I could post it here and see what, if any, the downsides would be.

Thanks,

[Brandon Chew]

We don't have much of an issue with expansive soils in my area, but from what I understand about post-tension foundations, the primary purpose of building it this way is to add strength to the slab so that as the soil under and around the house moves, the slab stays in one piece. With that in mind, the first thing that jumps out at me is that the potential for differential movement between the foundation for the addition and the foundation of the house would be a big issue that needs to be addressed in the design. You'll either need to ensure that both move together, or allow for them to move independently of each other.

Brandon

[rlskfoster]

That is a very good thought, because, they would move independently of each other, I guess it could act like a hinge. The good thing for him is his particular area of North Texas is known for its rock and not clay. I know it is probably in his area, because North Texas full of clay and foundation repair companies, but, we laugh at how long it takes the utility construction to dig down the easements in his particular area. I think that he should plan on having a PE design this thing and not just have a concrete guy come out and poor a slab.

Thanks,