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miamicuse 04-24-2012 09:10 PM

Framing a wood studded wall against a concrete block wall
 
I need to frame a wall against a concrete block wall. This is a normal wood studded wall with a pressure treated bottom plate, top plate and wood studs spaced every 18".

The problem is the concrete slab is ever so slightly higher where the floor meets the block wall. So when I pushed a PT 2x4 against it as the bottom plate, the plate is not level. So the front lip of the 2x4 is a little lower than the back, may be by about 1/8".

Is this significant enough?

Do I shim along the entire front of the bottom plate to get the plate level? Or should I cut each stud a little skewed to account for the difference?

joecaption 04-24-2012 09:12 PM

Your not suppost to install the wall tight to the block anyway. Just move it out where it's flat.

miamicuse 04-24-2012 09:39 PM

I wish I could but I need that space.

cortell 04-24-2012 09:40 PM

1 Attachment(s)
Like Joe said, you definitely don't want to frame right up against the block. Go out at least an inch; more if you need it to reach the level plane. In between the block and the wall frame, install rigid foam. This provides both a thermal break and a vapor retarder. Make sure to tape the seams well. In between the studs, install batt insulation for a more substantial thermal break.

ben's plumbing 04-24-2012 09:43 PM

Quote:

Originally Posted by miamicuse (Post 906843)
I wish I could but I need that space.

you only need min distance from wall ..just not up tight to block....:yes:

Gary in WA 04-24-2012 10:20 PM

If a partition wall, just shim the top plate to framing above. Is it a garage wall, basement wall, or house on slab grade wall?

As it's on a slab (if on the earth) you need sill sealer under the bottom plate for a thermal/capillary break to prevent water wicking to the studs: http://www.greenbuildingadvisor.com/...-building-code

I hope the 18" layout is a typo...

If against an house exterior block wall, only a v.b. is required for untreated vertical studs touching concrete; http://publicecodes.citation.com/ico...9_3_sec017.htm

Gary

Charles S. 04-24-2012 11:40 PM

I've been in construction more than 20 years. Everyone is telling you the right thing; don't build it touching the block wall; or you run the risk of it rotting with the killer being the condensation which is the thing which prevents every exterior masonry wall to be dry every day and night when it's humid, dark and warm/cold alternating days, such as fall/winter/spring bring to various parts of the country. I've replaced roof plywood more than once due to those folks building a room up against the rafters, pressing the insulation, and not having a ventilation space for the condensation---which is going to form regardless---to be able to then dry out instead of turn to mold.

The sill might be done any of those ways, but you might find it easier to build the wall on the floor, then stand it up. Any spaces underneath the sill can be filled with shims at the 18" marks, maybe some liquid nail...

hand drive 04-25-2012 08:23 AM

Quote:

Originally Posted by miamicuse (Post 906800)
I need to frame a wall against a concrete block wall. This is a normal wood studded wall with a pressure treated bottom plate, top plate and wood studs spaced every 18".

The problem is the concrete slab is ever so slightly higher where the floor meets the block wall. So when I pushed a PT 2x4 against it as the bottom plate, the plate is not level. So the front lip of the 2x4 is a little lower than the back, may be by about 1/8".

Is this significant enough?

Do I shim along the entire front of the bottom plate to get the plate level? Or should I cut each stud a little skewed to account for the difference?

a few shims placed under the front of the plate along with liquid nails used underside along the entirety of the plate will help get it level.

It will most likely work best to bring your wall a 1/2" or so off of the block wall. that way you can make your wall vertically plumb regardless of the block wall. Also it is good to seal the block wall behind new stud wall if it has not already been sealed.

mystic_cobra 01-06-2014 05:35 PM

Quote:

Originally Posted by Charles S. (Post 906952)
I've been in construction more than 20 years. Everyone is telling you the right thing; don't build it touching the block wall; or you run the risk of it rotting with the killer being the condensation which is the thing which prevents every exterior masonry wall to be dry every day and night when it's humid, dark and warm/cold alternating days, such as fall/winter/spring bring to various parts of the country. I've replaced roof plywood more than once due to those folks building a room up against the rafters, pressing the insulation, and not having a ventilation space for the condensation---which is going to form regardless---to be able to then dry out instead of turn to mold.

The sill might be done any of those ways, but you might find it easier to build the wall on the floor, then stand it up. Any spaces underneath the sill can be filled with shims at the 18" marks, maybe some liquid nail...

Does this rule (no framing touching the exterior block wall) still apply if the exterior wall is a slab on grade garage wall that has been drylok painted?

CarpenterSFO 01-07-2014 01:13 AM

Quote:

Originally Posted by mystic_cobra (Post 1288227)
Does this rule (no framing touching the exterior block wall) still apply if the exterior wall is a slab on grade garage wall that has been drylok painted?

You mean that your block wall is above ground?

md2lgyk 01-07-2014 08:38 AM

Quote:

Originally Posted by miamicuse (Post 906843)
I wish I could but I need that space.

We're not talking a lot of space here (only, as noted, an inch or so). Why even consider doing it wrong just to gain that little bit?? If it's that important, do the framing with 2x3s. Also, 18" on center is not normal spacing; it's 16".

mystic_cobra 01-07-2014 09:58 AM

Quote:

Originally Posted by CarpenterSFO (Post 1288441)
You mean that the block wall is above ground?

Yes. I'm framing/insulating a concrete block garage. The walls are completely above grade with only ground contact coming from below the slab. Does this rule still apply? I've never had visible moisture inside the garage.

CarpenterSFO 01-07-2014 10:50 AM

Quote:

Originally Posted by mystic_cobra (Post 1288571)
Yes. I'm framing/insulating a concrete block garage. The walls are completely above grade with only ground contact coming from below the slab. Does this rule still apply? I've never had visible moisture inside the garage.

In that situation I wouldn't worry about the moisture much at all.

If you don't care the about the insulation that much, most builders would stick up a layer of plastic then just attach 2x on the flat to the CMU, as a nailer for sheetrock.

Next step up would be 1/2" foam on the CMU, then plastic, then the 2x's flat again, maybe using simpson A35s or A23s or the like to keep screws from transmitting cold out to the sheetrock (and showing condensation).

Next step up, if you wanted more space to run wiring and the like, would be to put the 2xs on edge (not on the flat).

For insulation value, the thing is to remember that wood is not a great insulator. If insulation is a key, I'd add more foam thickness before I switched the wood to on-edge.

How much insulation value do you need? What is the space going to be?

cortell 01-07-2014 11:05 AM

Quote:

Originally Posted by CarpenterSFO (Post 1288587)
In that situation I wouldn't worry about the moisture much at all.

I would worry about it, assuming the concrete block is exposed on the exterior side. The concrete block will absorb rain. Even if visible moisture has not been observed, that doesn't mean it's not there. You do not want framing making direct contact with any porous material that is exposed to the elements.

CarpenterSFO 01-07-2014 11:15 AM

So I'd put a vapor barrier in, but not worry about it much further, unless there's something unusual going on.

- Bob


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