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wesley8808 03-30-2010 12:09 PM

Shimming Walls in Basement?
I am about to start finishing my basement and have a question about the walls.

I have a poured concrete floor and there are inconsistencies in ceiling height even in an 8 foot span. I planned on prefabbing 8 foot sections with PT 2x4 as the bottom sill, assembling the wall and then leaning it in place. Is it acceptable to use shims to fill gaps between the top plate and floor joists above and nail in place? I am using a powder actuated gun to set the bottom plate. What distance is too much to shim?

Bob Mariani 03-30-2010 03:08 PM

no issues with the shims. But you are missing so many things here. Better read a lot more on finishing a basement if you expect it to last more than a few years. Normally you stick build the walls, not raise it. one stud at a time and then no shims are needed.

wesley8808 03-30-2010 03:27 PM

I am sure I will end up stick building in the end. A few friends in the construction industry advised me to take the measurements of an 8 foot span and prefab the wall for that section, if there is a gap to shim it.

I am not a remodeler by trade, but have worked on a good amount of basements/sheds/remodels over the years. I am reading as much as possible, but also want to save some time if possible. I do not intend to affect the integrity of the walls by any means. My basement is essentially level and I was speaking more of the one or two joists in the span. I appreciate the advise.

Bob Mariani 03-30-2010 03:38 PM

stick framing is the way to go. But read the docs on before you do this work. Some get confusing so post specific questions and we can help you get it right. We need to know where your are to do this. And what part is below grade and what part is above grade.

you need to use sill insulation under the bottom plate to provide a capillary break.

tpolk 03-30-2010 03:40 PM

non load bearing you can shim. best way is to cut each stud to fit. I used to nail a plate bock at each end on ceiling after floor plate was installed. would then pull chalk line plate to plate.set stud on edge of floor plate and rub narrow edge of 2x on chalk line and cut that leaving the line.install ceiling plate and up go the studs

firehawkmph 03-30-2010 10:54 PM

I don't see anything wrong with building your wall in sections and raising into place, as long as they are not load bearing. I do it that way myself, although I usually build them in 14 or 16' sections. I make the wall a 1/2" shorter to allow it to raise up without having to beat it into place. I then rip plywood to use as shims. I ramset the treated plate to the concrete floor and use either a framing nailer or sometimes screws to fasten through the top plate to the joists. I have never had one come apart. My own basement has been done for over ten years and still looks the same as when I did it.
Mike Hawkins:)

wesley8808 03-31-2010 09:52 AM

Why do I need sill insulation if I am using PT as the bottom plate?

I am in Baltimore, Md and the basement is all below grade. None of the walls will be loadbearing - the house above is already built (the basement is completely unfinshed with 4 concrete walls and a couple of steel I-beams across the middle and family junk!).

Thanks Mike, I like your idea and it will make construction much faster. I already have 1/2 ply cut in 4" strips from a previous project! Just need to rip them down.

Bob Mariani 03-31-2010 12:22 PM

why do you need PT... direct contact with WET concrete. It may look dry now but it is still drying the outside moist soil into the inside. This is the same reason you need a sill seal. Water will weep up (diffusion) through the Pt lumber into the studs and mold will feed on the paper of the drywall and be very happy (your kids will not be). Try it. make a small sample wall and set the PT in a puddle. If only people would understand some of their basic 7th grade earth science this would not be so confusing.

wesley8808 03-31-2010 12:25 PM

I am familar with concrete and the properties associated with it (I am a civil engineer by education (although not in job function)). Looking through the code, I see it only requires PT (I AM using PT on the bottom) on the concrete.

Anyone else have a thought?

Bob Mariani 03-31-2010 12:36 PM


Originally Posted by wesley8808 (Post 422204)
I am familar with concrete and the properties associated with it (I am a civil engineer by education (although not in job function)). Looking through the code, I see it only requires PT (I AM using PT on the bottom) on the concrete.

Anyone else have a thought?

By code? Good you get a passing grade of D. Do more reading and find out how many other things the code gets wrong. Still requiring inside poly vapor barriers in the South, yet this will only destroy the wall. And so many other things. Try my test and see what your wall will do with this water. Why do it wrong when you are getting experienced help trying to show you the right way. I spend my living fixing work done incorrectly, much of it by Code. Code allows a shower bed to have the waterprooifng membrane be in the mortar set into the weep holes. These clog in no time and within a few years the base rotws out and has the same bacterial makeup of a septic tank. (code has finally changed this in many locals). This code following without thinking cost the Bellagio hotel 54 million dollars to redo all the showers in Las Vegas. But here it is still code

wesley8808 03-31-2010 12:45 PM

Fair enough. It wouldn't difficult to lay it down first.

Bob Mariani 03-31-2010 12:47 PM


Originally Posted by wesley8808 (Post 422212)
Fair enough. It wouldn't difficult to lay it down first.

do it right... it is always easy when it is done this way the first time. What did you use against the foundation wall? How did you air seal the rim joists?

wesley8808 03-31-2010 12:57 PM

I have not even started yet. Still working on a plan. I have an architect friend doing some work on the side/under the table for me to help with the design.

The insulation was provided on the outer wall already with a wrap. It goes concrete-> insulation -> Vapor barrier. I am going to leave a 1/2" - 1" space between the insulation and the wall to allow for air movement. Years ago, I went through with spray insulation foam and sealed at the joint between the walls and the top of the concrete walls.

conudrum 03-31-2010 02:43 PM

Floating Walls
Make sure you don't have exspansive soil in your area!

Here in Colorado we have to "float" the basement walls, literally hang them from above with several inch gaps between the bottom plate and the PT sill, with spikes keeping the wall aligned. This allows the slab to move without moving the frame.

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