Uneven basement floor

javastu1June 30, 2008

I am framing a basement in 2x3 studs using pressure treated lumber for the bottom plate, which I intend to drive into the floor with a Ramset gun. This is my first framing project and I have already run into a problem. The concrete floor of the basement slopes slightly downwards as it moves away from the concrete walls. This makes the bottom plate slope as well. What to do?

The only thing I can think of is to measure the angle of slope and use a table saw to shave of the appropriate angle off of bottom of the plate so it'll sit flat on the basement floor. It sounds like there should be an easier way.

Can I shim the bottom plate - raising one end so that it lays flat? Do the shims have to be pressure treated as well?

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I've finished a lot of basements new and old and haven't come across that. It must be some steep slope that it's noticeable 4" from the walls! I'd place the base plates on 1" strips of XPS and not bother with p.t. Then shim o.c. where you intend to frame the uprights.

    Bookmark   June 30, 2008 at 4:06PM
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It is an old house and basement floor is quite regular except that it slopes slightly as it meets the walls. I have measured the angle and it is a mere 2 degrees. It doesn't look noticeable to the eye, but when you stick a vertical stud on a two degree slope it sticks out rather than go straight up to the top plate!

Doing a little trigonometry will tell you that for a 2 degree slope a 7 foot stud will miss the top plate by around 3 inches!

Shimming for every stud sounds like more work than need be.

After talking with some folks, I think I am going to set my table saw on a 2 degree angle and shave a little off so it lays flat.

    Bookmark   June 30, 2008 at 4:42PM
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Use 2 x 4s. For the increase in price, it is better lumber, straighter, fits more insulation,etc.

    Bookmark   June 30, 2008 at 10:18PM
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Use 2 x 4s

I didn't even notice that! I agree.

    Bookmark   July 1, 2008 at 9:48AM
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Well, a number of people have given me similar advice about using 2x4's because it accommodates more insulation. But hear me out...

Not only does the floor slope up slightly toward the wall, but there isn't a clean edge where the wall meetings the floor. It is not cinder block but poured concrete and the walls/floors have a very rough finish to them.

So no matter what size I use for the bottom plate, I cannot place the bottom plate snugly up against the wall. So using 2x3's I will still effectively have a depth of a 2x4 and possibly slightly more.

So will you guys now change your minds?

    Bookmark   July 1, 2008 at 1:05PM
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That raises another issue. Framing up tight against the concrete walls, then filling the space between the studs with fibrous insulation is a discredited, if still popular, way of insulating a basement. XPS, EPS or foam on the walls is the way to go. Then you can add whatever you want between the studs. But that's another whole topic....

    Bookmark   July 1, 2008 at 2:12PM
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Your bottom plate does not need to fit snuggly against the wall. If you are out of plumb, just move your wall out a bit from the wall so you can compensate and have a straight wall from the top to bottom. Set you top 2x4 and drop a plumb bob down to set the edge of your bottom plate.

    Bookmark   July 1, 2008 at 11:01PM
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How about beveling the bottom plate so that it will sit up against the wall. Let it set at whatever angle it wants to then cut the bottom of your studs to match so that they will go straight up. Have you checked the wall for plumb? You may have to move one of the plates out to get a plumb wall.

    Bookmark   July 9, 2008 at 10:03PM
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