Securing Studs and Shims

[ngen33r]

I have a situation where I want to lay studs flat against the wall. This is an interior wall that is not perfectly vertical. It is off by about 1/4in over 7ft. I have secured the studs with 1/4in tapcons to the block and shimmed them so they are as level and in plane as possible. I did not drive the tapcons through the shims so that I could make adjustments as needed. Should I glue or nail the shims in place and is it worth filling the gap between the wall and studs with foam or adhesive? 1/2in hardi backer and tile will go on the walls. All studs are on 12in centers with doubles at every vertical seam. This is the only wall that does not connect floor to ceiling.

 

[Reach4]

This is an interior wall

Do you mean that the other side of the concrete is not in contact with the dirt?

Closed cell foam insulation is good if the other side of the wall is dirt. Use sheets, and fill in gaps with the more-expensive foam.

 

[Sponsor]

 

[Dana]

If that's a foundation wall, current IRC code calls out R15 continuous insulation, or R19 if between studs. From a moisture control point of view you can either do 2.5-3" of rigid polyiso foam (reclaimed/used polyisocyanurate roofing foam is pretty cheap & effective- these folks probably have some), or 4" of EPS, or 1.5" of EPS (or 1" polyisocyanurate) trapped to the wall with a 2x4/R13 studwall snugged right up to the foam (no gaps where air can flow, vertically or horizontally.) The 1.5" EPS or 1" polyisocyanurate + batt studwall solution is cheapest if using virgin-stock foam.

There are some particulars to attend to with any of these solutions, but I'll refrain from diving in unless you're sure you're going to do it. There are multiple threads on this forum covering that topic, if you care to search them out. It's climate-specific- Cleveland OH is in US climate zone 5A.

Closed cell polyurethane spray is both pretty expensive (a buck or more per square foot per inch of depth, and it'll take at least 2.5" ) and not environmentally friendly (HFC blowing agents unless you seek out the very few using HFO1234ze as the blowing agent) and a high polymer-weight per R. It's great at air sealing the block wall, and sealing the band joist & foundation sill, but it's an expensive way to insulate a wall to the full code-R.

 

[ngen33r]

The other side of that wall is the other side of the basement. No dirt is on the back of that wall. The left side wall is an outside wall and uses standard partition framing and will have insulation between the studs. I am more concerned that with expansion and contraction the shims might become loose and the wall will not be secure anymore. I might just be over thinking this but I would rather have those thoughts now before I have problems down the road.

 

[Reach4]

I might just be over thinking this but I would rather have those thoughts now before I have problems down the road.

A thin 1-3/4 or 2 inch nail through each 2x4 into each shim that you might worry about could stop your worry. You could use finishing nails to avoid a head sticking up.

 

[Dana]

The other side of that wall is the other side of the basement. No dirt is on the back of that wall. The left side wall is an outside wall and uses standard partition framing and will have insulation between the studs. I am more concerned that with expansion and contraction the shims might become loose and the wall will not be secure anymore. I might just be over thinking this but I would rather have those thoughts now before I have problems down the road.

I've never seen a TapCon pull from a poured concrete wall from seasonal moisture expansion/contraction of shims and I doubt it's any worse with CMU blocks. You're definitely over thinking this. Most people would use 1x4 furring + shims rather than 2x.

BTW: Codes usually require at least some sort of top plate , and sometimes fire-blocking near the mid point in partition walls to limit fire spread when there is a hidden empty vertical cavity. Probably not much risk here, but it might be a requirement.

Is the left wall 2x4 framing butted up to another CMU wall, or is it a plywood sheathed exterior wall with siding?

 

[ngen33r]

I've never seen a TapCon pull from a poured concrete wall from seasonal moisture expansion/contraction of shims and I doubt it's any worse with CMU blocks. You're definitely over thinking this. Most people would use 1x4 furring + shims rather than 2x.



BTW: Codes usually require at least some sort of top plate , and sometimes fire-blocking near the mid point in partition walls to limit fire spread when there is a hidden empty vertical cavity. Probably not much risk here, but it might be a requirement.


Is the left wall 2x4 framing butted up to another CMU wall, or is it a plywood sheathed exterior wall with siding?

I went with 2x4 laid flat because the cost was not much more and I wanted the added strength with the shimming. The top of the wall is shimmed out over an inch in some places. My concern was if the shims came lose and fell out the wall would be unsupported. Highly unlikely but possible.

602.5 Interior nonbearing walls. Interior nonbearing walls shall be permitted to be constructed with 2-inch-by-3-inch (51 mm by 76 mm) studs spaced 24 inches (610 mm) on center or, when not part of a braced wall line, 2-inch-by-4-inch (51 mm by 102 mm) flat studs spaced at 16 inches (406 mm) on center. Interior nonbearing walls shall be capped with at least a single top plate. Interior nonbearing walls shall be fireblocked in accordance with Section 602.8.

Left is another CMU wall below grade with dirt on the other side. The partition is spaced 3/4 in from the wall. The bottom plate is pressure treated and the wall is secured to the floor and ceiling joists

Technically I am using the 2x4 as furring strips for that back wall. The install instructions for the cement board call out for 2x4 framing on 16 centers max but don't say they cannot be flat laid. I guess it is confusing because what I am trying to do is not called out.

702.3 Gypsum board.
702.3.2 Wood framing. Wood framing supporting gypsum board shall not be less than 2 inches (51 mm) nominal thickness in the least dimension except that wood furring strips not less than 1-inch-by-2 inch (25 mm by 51 mm) nominal dimension may be used over solid backing or framing spaced not more than 24 inches (610 mm) on center.

702.4 Ceramic tile.
702.6.2 Furring strips. Where furring strips are used, they shall be 1 inch by 2 inches or 1 inch by 3 inches (25 mm by 51 mm or 25 mm by 76 mm), spaced a distance on center equal to the desired exposure, and shall be attached to the wall by nailing through other wall material into the studs.

718.1 General. Fireblocking and draftstopping shall be installed in combustible concealed locations in accordance with this section. Fireblocking shall comply with Section 718.2. Draftstopping in floor/ceiling spaces and attic spaces shall comply with Sections 718.3 and 718.4, respectively. The permitted use of combustible materials in concealed spaces of buildings of Type I or II construction shall be limited to the applications indicated in Section 718.5.

718.2 Fireblocking. In combustible construction, fireblocking shall be installed to cut off concealed draft openings (both vertical and horizontal) and shall form an effective barrier between floors, between a top story and a roof or attic space. Fireblocking shall be installed in the locations specified in Sections 718.2.2 through 718.2.7.

718.2.1. Fireblocking materials. Fireblocking shall consist of the following materials:

1. Two-inch (51 mm) nominal lumber.

2. Two thicknesses of 1-inch (25 mm) nominal lumber with broken lap joints.

3. One thickness of 0.719 -inch ( 18.3 mm) wood structural panels with joints backed by 0.719 -inch ( 18.3 mm) wood structural panels.

4. One thickness of 0.75 -inch ( 19.1 mm) particleboard with joints backed by 0.75 -inch (19 mm) particleboard.

5. One-half-inch ( 12.7 mm) gypsum board.

6. One-fourth-inch ( 6.4 mm) cement-based millboard.

7. Batts or blankets of mineral wool, mineral fiber or other approved materials installed in such a manner as to be securely retained in place.

8. Cellulose insulation installed as tested for the specific application.


Can a top plate also count as fire blocking?

I would tear out the wall and start over, but I do not have the 3in spacing to use a 2x3 for a standard partition wall due to the location of the drain for the shower pan. I can add a top plate, but is it required for furring? Typically I see 1x3 furring strips ram set into the blocks but this is a different animal. I definitely want to make sure that I do this the proper way so it lasts and looks good.

 

[Dana]

A 2x4 top plate with a 1x 4 on top of it (2.25" total thickness) would qualify as a fireblock, as long as they're both one full length of lumber, not segments scabbed onto each other. Fiberglass batts compressed into 1.5-2" with a tight fit would probably qualify at some minimum length too (I think 18" might be only 15".)

If the lean of the wall is pretty consistent you could angle-cut the 2x4s on the long axis to make a reasonably vertical & flat surface when butted up to the CMU, then build it up as a conventional studwall with odd-ball stud dimensions, and it would require less shimming. As long as it's still 1.5" or so on the skinny end of the stud it should be OK.

On the as yet uninsulated foundation wall 3/4" away from a 2x4 studwall, to insulate that adequately without creating a mold farm you're probably going to have to use about an inch of closed cell spray foam on the CMU, thick enough to seal to the exterior stud edges. At 1" most 2lbs closed cell foam is between 0.8-1.5 perms, which keeps ground moisture from accumulating in the studwall. That's also going to be about R6, of foam give or take. With R6 foam on the exterior you can then insulate the stud bays with unfaced or kraft faced batts (R15 max) without risk of wintertime moisture from the interior condensing on the foam and making the fiber insulation wet at the above-grade section of that wall.

The alternative is to try to somehow slip sheets of 3/4" polyisocyanurate board (R5) and seal them well, and limit the cavity R to R13s.

An R13+ R5 continuous insulation wall meets the IRC code minimum performance requirements for basements on a U-factor basis, and is far more moisture resilient than a code-in 2x6/R19 with a vapor barrier (= moisture trap). Installing batts in the 2x4 wall without the foam has thermal performance issues related to convection into and out of the batt from the 3/4" air gap, and won't even perform at it's rated R, which is itself a bit shy of code min. (And there is still the fire blocking issue...) With basement walls you have both ground water and wintertime moisture accumulation issues to deal with, and installing sufficient exterior side foam-R for wintertime dew point control for the local climate fixes both.

If it's only a couple hundred square feet of CMU wall it's going to be cheaper (though still expensive) to buy a DIY closed cell foam kit, and just follow the instructions carefully (pay attention to the limits on chemical tank temperatures and surface temperatures). If it's over 600 square feet it's usually cheaper to let a pro do it, even though they'll whine about setting up for any thing under 1000 board-feet, and charge you 1$1.5-2 per board foot rather than the buck a board foot they charge for 5000+ board foot jobs. (You can't blame them too much- it takes just as much time to set up and break down for 500 board feet of foam as 5000 board feet.) Be sure to foam up and over the top of the CMU to seal & insulate both the band joist and foundation sill with an inch of foam too.

Kraft facers on batts are OK- they become vapor open when it's damp enough in the cavity to support mold, but not foil, which is too vapor retardent and could trap moisture. The "contractor roll" R13s are usually pretty cheap. If the basement has a history of flooding you might want to stop the batts at the high-tide mark. As long as the batts are installed carefully for a full fill, tucking them in to framing on the sides & top and at the corners, then tugging it out until it's just proud of the stud edge for a compression fit to the wallboard, gap on at the bottom of the stud bay won't contribute to a convective thermal bypass around the batt. Don't use anything more vapor retardent than latex paint on wallboard for the interior finish, so that any ground moisture that gets through the foam or the bottom plate will dry toward the conditioned interior space.

 

[Jadnashua]

A top plate should be okay for fire blocking. You could put some construction adhesive on the shims...once it sets up, they won't go anywhere.

 

[ngen33r]

I am going to add a top plate and remove a couple studs so I can fit some sheets of R5 behind the studs before adding insulation. I always thought it was better to have free air not trap the moisture but I guess that is not the way to do things.

 

[ngen33r]

While I have the support. Ohio code states to follow the manufacturers instructions for installing cement backer board. The install sheet states that a vapor barrier is optional. I do not want to trap any moisture and definitely don't want any mold. Should I leave the vapor barrier off behind the backer board so the moisture can eventually find its way to the air and dehumidifier? I know it is a shower and not a swimming pool, but eventually some moisture will wick through the grout and into the cement board.

Also Great Stuff makes a spray foam fire block. Is that as good as using a scrap piece of drywall? Still absurd that I need to do that. Unless bugs learn to make fire or someone removes a ceiling panel and flicks a cigarette over the block wall and down behind the shower.

 

[Jadnashua]

CBU is not waterproof, it is not damaged by being wet. The Tile Council of North America (TCNA) calls for a vapor barrier behind a cbu wall OR surface applied waterproofing on top of it. There will be some moisture that penetrates the cbu, more near the lower parts of the shower than at the top. If you build your conventional shower and embed the cbu in the setting bed...the cbu will wick some moisture up from the setting bed, so you really do want a barrier behind it, or to waterproof the entire shower with a surface applied membrane.

IMHO, you could avoid all of that and even use drywall on the walls if you use either Kerdi or HydroBan sheet membranes on top of it...that makes the entire shower waterproof right underneath the tiles. You can use CBU if you wish, but those two sheet membranes have been tested and certified to be waterproof when used over plain drywall (and cbu). This takes a different drain than a clamping drain and a conventional liner. There are a couple of waterproof, tileable, foam panels that could be used as well: KerdiBoard and WediBoard. Neither of these is really 'new', since they've been around for decades, but tradition is hard to break.

 

[Dana]

I am going to add a top plate and remove a couple studs so I can fit some sheets of R5 behind the studs before adding insulation. I always thought it was better to have free air not trap the moisture but I guess that is not the way to do things.

With exterior basement walls there are two moisture drives that need to be dealt with, groundwater coming through the below grade section 24/365, and winter time moisture condensation on the above grade section. Adding an air channel behind the insulated studwall can only purge the ground water condition if there is convection around the studwall, which would undercut it's thermal performance severely.