Framing walls on an unlevel concrete floor?

[Matt Meiser]

I'm planning to frame walls for my finishing room starting later today. As expected the floor isn't perfectly level--actually on purpose so water runs toward the sliding door. I checked with a laser level and a tape measure and it appears to vary about 1/2" from the lowest spot to the highest. So, in framing these walls, I'm wondering if, and how I should deal with the variance? The 1/2" variance is across about 9' at the side wall of the building to the lowest spot in the center.

[Bob Riefer]

My barn is ridiculously crooked in all directions. I've gone two routes that have worked well for me. One, I've cut each stick individually and toe nailed them in. That's works but is time consuming if you have a lot of walls. Two, I've also built a square wall on the floor, stood it up, and shimmed. Also works and is much faster. Just use shims that won't rot/deteriorate if you're shimming at the ground (I liked pieces of asphalt shingles).

edit: for a large 1/2" drop that I just noticed in your post, you could also consider scribing a bottom plate to fit flush to the floor, then build a square wall and set it on top of that. I'd just shim it though as the wall is not structural.

Side note, I like PT lumber for wood in contact with concrete. For attaching, non structural, I just use some liquid nails and the ramset.

[Matt Meiser]

Yes, I'm using PT lumber at the floor. Luckily I have nails for my framing nailer rated for the new PT lumber--didn't think about that before I ordered it. I was going to put a heavy bead of silicone under the bottom plate of the wall that divides the finishing room from the tractor storage area to prevent any snow melt from running under the wall if it doesn't go the right way toward the door.

I did the cut to fit method in my basement when I built a wall down there. I bought precut studs before thinking about this issue. Luckily at all the outside walls it seems to be consistent at 1/2" high. I still have to frame those since its a pole barn and I need something to hold the insulation and drywall.

[Dan Hintz]

'Twere it me, I would shim the sole plate level and build as normal... I use liquid nails and the ramset nails with PT, just in case.

[Kent A Bathurst]

FWIW - Some time ago, I had reason to check in with the structural engineering group of the company I worked for, and their answer came back that there really is no adhesive that is going to do much with PT lumber in terms of an actual, structural bond. Moisture content is the culprit, of course - you'd need to locate some KDAT [Kiln Dried After Treating] lumber, which is fairly unusual to find, and more expensive, of course. This stuff is plain-old PT lumber that then gets stickered and dried in a kiln. On the plus side - it will not warp and twist like regular PT lumber does as it dries. It exists, but you generally have to do some work to locate it.

The point - you definitely want to use mechanical fasteners with the PT sill plate.

[Jerome Stanek]

I would build with metal studs and track you don't need to be exact.

[David Larsen]

Start your PC studs at one end. Full PC for the first stud then cut 1/16 off the next. 1/8 off the next. 3/16 off the next. 1/4 off the next. 5/16 off the next. 3/8 off the next. 7/16 off the next. 1/2 off the next. That is 9 studs. That will get you 12 feet of wall if 16 OC.

Adjust accordingly if the wall isn't that long or is longer. Either way, you end up making up the difference over the length of the wall is what I am trying to explain. When you are done, only you will know that you did this and the top plate will be level.

No need to shim the sill plate. Use the silicon to waterproof it like you described.

[Larry Edgerton]

What Bob said.......

Larry

[Art Mulder]

Yes, I'm using PT lumber at the floor.

I'm (about to start) doing some minor framing in my basement shop, and my brother advised me to get Bluwood for the bottom plate instead of PT. The reasoning is that PT gives off toxic smoke if it ever were to burn. That may not be as much a concern in an outbuilding, but just thought I'd mention it.

[Dan Hintz]

I'm (about to start) doing some minor framing in my basement shop, and my brother advised me to get Bluwood for the bottom plate instead of PT. The reasoning is that PT gives off toxic smoke if it ever were to burn. That may not be as much a concern in an outbuilding, but just thought I'd mention it.
When PT was done using arsenic-based treatments, this might have been a bigger deal... but even then, are you really going to be hanging around a place that's burning to suck in the fumes? You would need to suck in a lot of fumes to have any lasting effect, and you're not going to get that level of contamination from breathing a few fumes while trying to get out of the house.

[Rich Engelhardt]

This same topic came up not too long ago here.

For anything that isn't load bearing that goes on concrete - I'm a big fan of floating walls.

Floating it removes any problems associated with an uneven surface, it's easier and quicker (MHO only) and it gives you peace of mind that if/when the concrete heaves it won't take the roof off - or worse.

[Larry Frank]

I just finished putting a wall in what used to be part of the garage and the floor was very uneven. I put down a pressure treated sill plate and shimmed it level and attached it to the floor with Tapcons. This allowed me to build a standard wall on the floor and then set it on top of the sill. I did not use any adhesive.

[David Larsen]

I just finished putting a wall in what used to be part of the garage and the floor was very uneven. I put down a pressure treated sill plate and shimmed it level and attached it to the floor with Tapcons. This allowed me to build a standard wall on the floor and then set it on top of the sill. I did not use any adhesive.

Did you double the bottom sill plate? If so, then you had to have cut 1 1/2 off each pre-cut stud to get the right dimension.