Non bearing slab on grade walls

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Old 02-10-13, 11:44 AM
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Non bearing slab on grade walls

Hello everyone

I'm finishing my basement here in Colorado within Douglas County. I'm currently at the beginning of the framing stage. Douglas County code says that all non bearing slab on grade walls must be floated due to expansive soil. I understand the floating part. What I'm a little confused at which walls should be floated. My friend thats helping says that any wall against the exterior wall is weight bearing and doesn't have to be floated.

Can anyone clear this up for me?



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Old 02-10-13, 12:17 PM
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Welcome to the forums! The basement walls that are exterior extend all the way to the slab. Any dividing wall beyond them must be floating. Not sure if that explained it or not. As always double check with Douglas County permit department to make sure you are within their parameters.
 
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Old 02-10-13, 07:16 PM
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Even a framed wall in front of a foundation wall, parallel to it, must be floating. That's because any wall resting on the bottom floor slab is prone to move up and down with the floor slab when it moves up and down. The foundation walls shouldn't move, as they do not rest on the slab, but rather are supported by footings (hopefully) resting on non-expansive material.

Don't listen to your friend. Doing so could raise your house up and off the foundation, under the right (but adverse) conditions under the slab floor. Problems can be minimized by making every effort possible to minimize moisture accumulation in the clay soil under the slab. Dry clay doesn't expand.
 
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Old 02-11-13, 04:34 AM
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Thanks for the response. I failed to mention that this is a walk out basement. The exterior walls are part of the foundation so its concrete resting on concrete. Also the house has been standing for nine years. Is it true that after nine years if the slab is going to move it will have done so already?

Floating the walls is no big deal and I certainly don't want to cut corners. I'm only concern because on one particular wall I plan on frame for a 80" TV. Another wall will have cabinets attached to it.
 
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Old 02-11-13, 09:07 AM
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The house's age has nothing to do with it. And the concrete-on-concrete foundation you mention has nothing to do with the slab, which is constructed separately from the foundation. The slab can heave after being dormant for a long time, if moisture conditions in the expansive soil under the slab change (increase). One simple plumbing leak is all it would take, or a change in how the gutter/downspout water is handled, or even a new planting area someone decides to put in and then over-water.

Play it safe, and build ALL of the basement's walls floating. Your building department will require it anyway.
 
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