I have a walkout basement with a very cold exterior wall in Zone 5 Michigan (Although it was closer to zone 6 with last years winter!) Right now, from inside to outside Brick Facade Tyvek Sheating R-13 Fiberglass in 2 x 4 Bays Drywall Since the wall is both load bearing and has large windows and a doorwall, I'm thinking that there is alot of 2x4s in the wall, and thermal bridging may be one of my issues. This is my suggested replacement Remove drywall and fiberglass. Caulk or foam any penetrations in the sheathing. Add 2" XPS in open stud bays and caulk or tape edges (I've read that cutting loose and using canned spray foam is a mess?). Next, I would take 1" XPS and cover the whole wall over the studs, nailing to the wall and taping the seams. I would then make a "fake" 2 x 3 stud wall to go right up against the 1" xps, staple 3 1/2" R15 fiberglass here, and then drywall. I know foamboard is best on the outside, but no way am I removing brick. Any thoughts on this approach? I've seen variations of this with out the true second wall (Just having the drywall shimmed over XPS board), so this seems like a valid extension of the approach?

both thermal bridging and low insulation levels will increase heat loss, so your improvements will help (although you should use EPS in your assembly to increase vapor permeability) but if the wall "feels cold", it is probably leaking air. So the first step would be to find the air leaks. A blower door is the idea solution; if that is unavailable or impractical, you can rig one up by installing a large fan in a window, and taping the edges so it is air tight. It should blow out, so it will increase infiltration and you will be able to find leaks with a smoke pencil (incense also works, but be very careful about fire)

The second test would be with a theatrical fog machine which you can probably rent from a good rental store. Set the fan to blow IN, start the fog machine, and go outside and watch for the fog to show you where the air is coming out. Hard to see in bright sun, but otherwise these work very well.

I'd consider just taped XPS over the studs and then drywall (ie, the variation you mentioned). Perhaps with the cavities filled with dense packed or wet sprayed cellulose instead of fiberglass. Consider air sealing supported by blower door tests (probably a better ROI). (edit: Bob's response came in while I was typing).

Bob, there is an outlet and two light fixtures on the outside of the wall. I'm 99% sure that these are big trouble spots. I figure with the drywall off these will be pretty obvious. Is the moisture concern because I am suggesting two layers of XPS? I thought that in this climate the sheathing should dry outwards, particularly with a brick wall.

For the makeshift blower with the window fan, I would still need to have the drywall off for it to be most effective?

jonr, I've seen some people mention this, but I'm concerned about drywall popping with expansion. If I use EPS I'm guessing it would be worse.

EPS is more permeable than XPS. Ideally, the wall should be able to dry to the inside as well as the outside.
You do not need to remove the drywall to test, although it would be more effective with it removed.

My understanding is that with the minor temperature variations that interior foam sees, they are quite stable in thickness. But I don't have figures for the various types of foam. I see some talk about exterior foam not being stable enough in length and width for tape to be a reliable option for air or water sealing. If that's also true of interior foam, then you might want to use a taped membrane such as CertainTeed's "MemBrain" or two foam layers with staggered joints.

Pressurizing and depressurizing a house while looking at it with a thermal camera makes sense to me for finding leaks (although not in mild weather).

There is no advantage to cut'n'cobbled foam in the 2x4 stud bays- it only complicates the assembly, costs more, and puts the sheathing at higher risk.

Instead, air-seal the sheathing to the studs with acoustic caulk (use can foam to seal any stud or sheathing penetrations by plumbing & electrical), and install either cellulose or unfaced R15 rock wool (preferred) or R15 fiberglass (which is fine.)

You can then put either 1" XPS or up to 3" of unfaced Type-II EPS on the interior side of the studwall, with either furring or fiber-insulated 2x3 wall on the interior side of the foam. It's important for the foam layer to be air-tight, and it may be worth using something like housewrap detailed as an air barrier between the foam & exterior studs, since unlike rigid foam, it can't shrink or crack over time.

You can't stuff R15 batts into a 2x5 stud bay very easily- they're way too dense & springy, and compressed to 2.5" they won't perform anywhere near R15- in reality it'll be about R11, per the manufactures' compression charts:



The easiest batt solution for the 2x3s would be to either buy R8 batts (designed for 2x3 studs) or compress unfaced R13 batts into it (they will perform at about R10 at that level of compression.)

With 1" of XPS or 3" of EPS  it becomes a 1-perm vapor retarder, but at a reasonable location within the stackup from a wintertime moisture accumulation point of view. But with any brick veneer wall it's important that the cavity between the brick & sheathing be vented to the exterior.  A bit of investigation is in order sometimes the cavity is blocked at the top, sometimes it opens into a vented attic, but in all cases at a minimum it needs weep holes in the bottom course of brick (usually a gap or drilled hole in the mortar) as well as some venting near the top, to allow convection to pull outdoor air through the cavity.  This keeps the average humidity in the cavity close to the average outdoor air humidity, allowing the sheathing to dry toward the exterior.  With out the venting there will be times/seasons where dew or rain-wetted brick create mold conditions inside the cavity, since the brick can store a substantial amount of water.

Dana1, thanks for the reply. Is MemBrain a good choice for the wrap suggestion? I've seen it at the local Menards so I know I can get it.

I know there is a gap between the brick and the sheathing, but there are no drilled weep holes. The Brick extends up 1 level, then has a "capping layer" with a slight slope downwards. There is an L-shaped flashing layer, and then the second story is board and batten siding. I've always thought that there is a gap near the flashing for drying. I'll have to see if there are any water issues when the drywall comes down.

It's not clear that this stackup would even need a membrane vapor retarder, but MemBrain would allow either side of the assembly to dry in either direction, whereas poly would not. But Tyvek/Typar type housewrap would serve equally well as an air barrier, for typically a lot less money.

If there are no vents from the cavity to the exterior, add them, both top & bottom. It doesn't have to be a lot- a 1/4-3/8" hole every few feet on both the top & bottom courses is usually enough. If there is zero over hang to the roof and the brick gets a lot of rain-wetting it may be worth coring in some 1" vent holes with a masonry hole bit and popping in the little screened vent caps to keep rodents & larger insects out.