Framing on slab

[jdhen]

Can I get some opinions on wall framing on a cement slab?
I can't find much detailed information focusing on framing over a slab.  Most books are geared toward pier and beam and framing on the floor deck.
In the book, Precision Framing, they do have a section on slab framing and they talk about the need to vary the stud lengths to compensate for unevenness of the slab.  My plan had been to gang cut the studs for the let-in ledger as illustrated by PEG, but if I have to cut all the studs to different lengths this won't be possible.
Anyone have any thoughts on this?
Somewhere I thought I read something about using shims under the wall to compensate for unevenness but I can't find that reference again.
Need some opinions from folks who have done this before.  Are slab undulations a big problem?
Thanks.

[glenn kangiser]

I haven't seen that done much around here.  They just put PT n the bottom and shoot or anchor it down to the slab - probably don't shoot them down much more with the more restrictive codes but thy used to. 

The city required caulking under the PT bottom plate. 

I didn't do a lot of it - offices in steel buildings - remodels and my own stuff.

PEG and others are pros on this - listen to them rather than me.

[PEG688]

If you set-up your forms right as in flat and level and use a straight screed board to screed off the concrete your slab , especially at the edges where the exterior walls go should be quite flat.

  That being said you will have some humps , but they should be slight.


  The  PITA about framing on slab on grade is figuring out a way to hold the bottom plate straight while racking the wall to pull it to square.


  With platform framing you can tack / toe nail down the bottom plate to the wood floor , then pull for square , then sheet the wall laying down.

 

  There's  couple of ways around this issue , both will be some what difficult for me to write down in a understandable way.

  IF your poured your own slab and know it's off / wavy. What you could do it cut and lay the PT plates then shim those up where required to get them flat and level. Then frame your wall with a regular / non -treated sub - bottom plate, so you'd have two bottom plates , the PT bolted down the sub-plate nailed to the PT with galv. nails.

That way your wall is flat.

  Another way would be to frame , but not sheet the wall with a  single PT bottom plate , tip the walls up , rack to plumb and then , either with a dry line or laser / builders level, do the same shimming of the plates to get the tops flat or level , then sheet the walls standing up.

  Confusing eh , read it a few times , ask questions where required. Maybe some one else can chime in or make more clear what I'm saying. If you don't know the terms I used a good  framing book would be Modern Carpentry , there are others as well.

Or like I said just ask what does " enter word here" mean?

  If you haven't poured yet you should think thru that process or maybe hire the labor for the pour , things are coming down in price as folks are hungry in the trades these days.

G/L PEG         

[PEG688]

Like Glenn said you want to bolt it down and put either the foam used for under sill plates down or use const. adhesive or caulking under the plate. You can also caulk the inside of the plate to concrete floor after the roof is on. IF you get inspected he'll want to see that bottom plate caulked / glued down on the interior to seal that joint anyway.

   

[MushCreek]

Here in FL, they usually cast J bolts in the slab, pre-drill the bottom plate, and use the bolts to hold it down. As said before, shims are used to level things up. I'm going to go one step farther when I build my barn in SC. I'm going to have walls either poured, or block, to bring it up 24", then go up from there with the wood. Otherwise the same- J-bolts cast in place. My sheathing will come down to cover the wood/concrete joint. Why the raised walls? Termites! I would never build directly on a slab in termite country, although I don't know where you are building. Not to discourage you, but after living on a concrete slab for the last 30 years- never again. It's hard on the feet and back. That slight give of a suspended floor makes all of the difference. I once read that when they built the Lincoln Center, when they booked a ballet troupe, they refused to dance on the concrete stage- a raised wooden floor had to be built. Just my $.02.

[tc-vt]

Another idea for a foundation wall or in your case, slab, that is not level is to bed a pressure treated sole plate in wet cement to level.  Make sure the j bolts you use are approved for use in the new ACQ PT lumber.  When you are sheathing, make sure to use approved fasteners at the bottom EDGE  of the plywood where the nails will be going into the PT sole plate.  If you double the sole plate and use a regular non-PT plate on top of the PT, you can nail the bottom row of nails into the non-PT without worrying about corrosion from the ACQ.

Tom

[Don_P]

I have had to put up a post at each end, bolt down the sole plate on the wavy floor, pull a TIGHT string and meaure each stud length, arking those on the plate. The top of your studs are in a straight line, the bottoms vary but not the tops. This is your reference end to straighten against and measure from when doing any further gang machining  .

[jdhen]

I just love this forum! 

Every time I post a question I get a number of great answers that help to clear things up for me.
Thanks to all that responded.

We closed on our land last week.  I will begin work on the pole barn this week and will start soliciting bids for the foundation.

Hopefully framing will begin sometime in July!  I'll set up a thread in the owner-builder section as that gets closer.
More questions to follow.....