Framing Basement Walls
Summary: Framing basement walls is a challenge when working on slabs poured over expansive clay bentonite soil. The walls need to float so they are not squeezed if the soil expands and pushes the wall upwards. There is a very simple trick that solves the problem and allows you to build strong walls that can move upwards, but not tilt over.
DEAR ART: Gosh, if your basement slab is moving up and down at a greater rate than the actual foundation walls because of the expansive clay soil, you might have all kinds of serious issues down the road. But let's not concern ourselves with that right now as there are ways to stabilize expansive clay soils so the movement is eliminated or minimized.
The trick to framing basement walls that rest on slabs in contact with expansive clay soils is to ensure there is a space between the top of the wall and any floor joist above. The space can be as little as 3/4 inch or up to 1.5 inches. At first blush, you might see a problem as the top of the wall would be flimsy and tilt or tip over when something pushes against it.
A simple L-shaped steel framing clip solves the problem. This clip is used by professional builders and rough carpenters for basement walls and roof trusses. Roof trusses in cold climates also present the same problem. During cold weather, the horizontal bottom chord of a wooden roof truss can bow upwards. If the interior walls are tight to the truss and nailed to it, the walls can lift up along with the moving truss and all sorts of havoc occurs.
The L-shaped clip is nailed tightly to the top of the wall, but it has long slits in the vertical leg that rest against a floor joist, truss or solid blocking between trusses or joists. Nails are driven through the slits into the truss, joist or blocking. This connection keeps the wall from tipping over, but allows the wall to move up and down as the slab moves.
These clips are inexpensive and you must use special structural nails that are made by the same company that manufactures the clip. Do not use roofing nails as they are not as strong as the thicker, structural nails.
Expansive clay soils can be stabilized, if you maintain a steady or constant level of moisture content within the soil. These soils shrink and swell in response to the loss and gain of water. Installing irrigation piping in the soils allows you to add water to the soil during dry spells or periods of drought. Since the soil stays wet year-round, it doesn't move.
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Comments:
dave koepcke 06 Jan 2008, 18:45
what do these framing clips look like? and where do you buy them .how far
apart do you set them? When building a basement wall do you need a double
top header? Dave
AsktheBuilder 06 Jan 2008, 20:27
Dave,
You buy the clips at any lumber company that sells steel framing hardware. Place them every 24". Single top plate for non-load-bearing walls.
dan 29 Jan 2008, 10:39
My daughter is looking at a house
in Munroe Falls, Ohio. The question that we have is when we went though the house (bi-level) in the basement there was a wall 3 feet high and 3 feet away from the wall. We were wondering if maybe if there could be a problem with this house? Thank you for your help
AsktheBuilder 29 Jan 2008, 13:26
Dan,
Possibly. Read my past columns about Home Inspections and Inspectors. Be sure you pay attention to when I mention ASHI.
Chuck P. 29 Apr 2008, 22:40
I am reading about the L shaped clips for basements with clay soil. How
would I find out if I have clay? Or should I just use the clips just to be
safe? Thanks
hank togna jr 19 Aug 2008, 08:38
I have redone my basment (heetrock)
i need to put up one potition of the side for walk in closet there is a new type of vinal wall material, just glue to the studs? what is it called? Hank Tgna Jr 973-724-6079 work
Jasmeah 25 Sep 2008, 11:42
Hi I was wondering if you can help me on how to bring a wall out and back
in. Thanks
Richard Fredericks 29 Sep 2008, 11:19
finishing a basement, should I install a vapor barrier on outside walls?
Dawn 22 Jan 2009, 11:38
We live in an area with high expansive soil. Our basement has a concrete
floating structural floor. Is it still necessary to use the L-shaped clips
when framing the basement walls or is it safe to assume the concrete floor
will not shift?
robert 22 Feb 2009, 15:41
i was trying to come up with something to cover a dirt basment floor. i can
not put in a cement floor can you help me out with something to cover the
dirt basment with
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