Wall insulation remodel question

[makethatkerdistick]

Ordered myself some of those fancy quad pane windows to replace my old 1960s aluminum single-pane nonsense. Now I am rethinking wall insulation on those spaces, too. Kind of silly to have a window with a U factor of 0.12 in a wall that is worse than that. I am planning of adding a combination of foam sheets and rock wool to a level of approx. R-18-21.

My current construction is non-pressure treated 2x4 framing in direct contact with the concrete slab. In a past project, I needed to replace the bottom plate due to termite damage, and at that time I rebuilt with dried pressure treated lumber AND a capillary break between slab and framing wood. Actually, I used some left-over Kerdi band, haha!

Now, with the rooms I want to remodel now, the bottom plate is fine and has no rot. I am afraid that applying foam to the cavity and possibly adding a 1 inch foam sheet to the interior of the wall might create moisture problems. On the other side is exterior gypsum board, an air gap and brick veneer.

I am trying to add a capillary break of any type to my bottom plate to prevent moisture migration. What would you do?
I was trying to pry up the plate a bit and hopefully tuck small sheets of aluminum flashing under. Or is there a better way, short of completely rebuilding (which I would hate to do). Perhaps squirting some Abatron Liquid Wood between the plate and the concrete, with the hope that it will flow all the way under the 2x4? The epoxy would be a capillary break I would think.

[cx]

Originally Posted by Wolfgang

Kind of silly to have a window with a U factor of 0.12 in a wall that is worse than that.

Wolfgang, I generally find your building science arguments to be well researched and well founded. This time, though, I don't think there is any way you can reasonably justify the expense of those windows, especially on a remodel. If you're doing it just because you can, of course, none of that matters, but I still think the cost/benefit just doesn't fall into the reasonable category. Not sure I could have even built that into my new construction, which was usually with 2x6 exterior walls, without some real "salesmanship." And, of course, they weren't even available. Hell, I was a pioneer down here in use of Low E glass back in the 80s.

Originally Posted by Wolfgang

Now, with the new rooms, the bottom plate is fine and has no rot. I am afraid that applying foam to the cavity and possibly adding a 1 inch foam sheet to the interior of the wall might create moisture problems.

Not following the thinking there. If you manage to create moisture problems in your walls, a moisture barrier or capillary break between sole plate and foundation slab isn't going to help with that. What am I missing there?

Sounds like your house has a new addition (?) and the new foundation had a proper vapor barrier material under the concrete. That could certainly account for the lack of problems with the sole plates. Is that the case?

[makethatkerdistick]

CX, I typed in haste with lots of clarity to be desired. Sorry. I am putting those windows in for comfort and because I can. Nothing else. Not concerned about payback. Price with self install is cheaper than having mediocre windows installed by someone else. That’s a fact.

Anyway, this is all 1960s construction. By “new” I was referring to the new wall insulation project, as opposed to the other rooms I have already done. So, the core of my question is: How do I add a capillary break between existing bottom plate and slab? My slab passes a bit of moisture, as I anecdotally gathered. I want to prevent transfer of water into the bottom plate while I have the walls open. What’s the best way to do that? How would you do it? Maybe I would get away without doing it, but it’s good insurance against trouble, methinks.

Don’t deride me for my window choices. If you have ever spent some time in front of a super insulating window on an extremely cold or extremely hot day, it makes quite a difference. Look at it this way: I could have gone for the quintuple glazing. I was still quite reasonable.

[cx]

Originally Posted by Wolfgang

I am putting those windows in for comfort and because I can.

No derision intended, Wolfgang, now or any other time. That sentence 'splains it all.

Originally Posted by Wolfgang

Price with self install is cheaper than having mediocre windows installed by someone else.

And I certainly couldn't conjure up an argument with that!

I honestly can't give you a suggestion for your sole plate issue. I think it's unlikely you could raise them far enough to effectively get anything useful under them. Lots of wedges might do it if you can loosen the nuts on the J-bolts, but there's certainly the possibility of doing other damage with that. Were you my customer, I'd most likely point out that if the plates have lasted since the '60s, they're likely to to further outlast you. At which point even you wouldn't see them as a problem, eh?

[makethatkerdistick]

Hi CX,
The plates have lasted so long due to a multitude of factors, I presume. The most obvious is that the cavity insulation is poorly installed, and so there is a lot of air leakage in the assembly. While that would promote condensation issues at times, it also allows for adequate drying.
Another reason is that while we are officially in climate zone 3A, the humidity is not as bad most of the time as it could be in an “A” zone.
Lastly, those sole plates are only secured to the foundation with nails. Yes, that is true! While they embedded some bolts in the concrete, they failed to put a washer and nut on to tie the framing down! Lazy and sloppy! As I am redoing the walls, I am adding bolts to tie them down. Of course, tying them down results in closer contact between slab and sole plate.

Maybe pushing pieces of aluminum flashing underneath in small segments is viable enough. I have done it before with another wall with an 80% success rate.
Rebuilding the entire sole plate is probably insane. What do you think of the epoxy squeeze in between / injection method? Abatron’ Liquid Wood is quite… well… liquid. To do either the aluminum flashing or the epoxy, I wouldn’t have to lift the wall much. Technically just 1/16 in (in segments) would suffice.

I plan to flash the cavities with 1 in foil faced polyiso boards, foamed in place by can foam, then trimmed neatly. Then I will offset that lost space by gluing strips of 1 in foam board onto the framing (from the interior, just to clarify). Then R 15 Rockwool insulation and drywall. Gives me a nominal amount of R21 and addresses thermal bridging and air sealing. I have in another room (with the rebuilt and properly capillary action-detached sole plate) added another polyiso board on top to increase insulation. This does, of course, eat up a tiny bit more interior space which I might not want to do during my new remodel project. Either way, this will be a radical comfort and energy conservation improvement t over the existing stuff.

I guess I forgot to address your initial question: I am afraid that by tightening the insulation and airsealing, the possible moisture migration from the slab into the sole plate cannot dry out as easily anymore when the assembly was very air leaky.Over time, this could cause problems.

[cx]

Very familiar with the Abatron product, and the WoodEpox that's used with it. Have done some serious restoration projects with them and am a large fan.

The Liquid Wood would certainly help protect the bottom of the plates if you can get it under there while the wood is very, very dry. I have frequently poured it into disposable syringes for similar applications. Just how far you can get it under there from only one side is a bit questionable, I think, but it certainly can't hurt if you can get some in there. Perhaps you can engineer you a special nozzle for such a syringe? Gonna be messy. And the Liquid Wood is not an inexpensive product. Not a big factor if you can make it work, of course.

Drying out wall cavities wasn't nearly the problem before we started making houses so tight we had to cut extra holes in the walls for make-up air.

[makethatkerdistick]

Thanks, CX. I will soon open up the drywall and see what I can do. Got some Liquid Wood left. Love that stuff!

Make-up air / mechanical ventilation is a great concept. It is controlled and predictable, whereas infiltration is not. I got a ventilating whole house dehumidifier. Great for the shoulder seasons when cooling load is low. Plus, the ventilation schedule blows air into the structure year round on a regular basis. Has worked well for years with little operating cost.

One thing I noticed with my deep energy remodel in my front room (where my piano is situated), is that these walls are much more resilient, also regarding humidity changes. Low air infiltration walls keep humidity in the house in the winter and keep it out better during warm humid times. The spruce tone wood of my piano’s soundboard loves the ensuing stability in humidity. Little change in pitch and doesn’t go out of tune, only minimally.

[makethatkerdistick]

I decided to replace the bottom plate and scab in a pressure-treated one (pre-dried in my garage for a year, so no twisting expected). Turns out, my oscillating tool was by far the most important device to make this possible!

I wrapped some left-over Kerdi membrane around the new plate in an L-shaped fashion to detach it from moisture migration from the slab. I then anchored it with 1/2 in concrete bolts, air-sealed with sealant, flashed the cavities with 1 in foil-faced polyiso boards and can foam. After trimming the foam, I glued strips of foam onto the framing members to achieve thermal detachment and avoid thermal bridging and regain the one inch thickness I had lost in the cavity due to the foam boards. I then filled the cavity with R-15 batts of mineral wool insulation. I love the snug fit of mineral wool!
Ultimately, I covered the whole assembly with 1/2 in board of “Foamular” (EPS foam) whose vapor barrier foil I removed prior (making the “Foamular” vapor permeable if slow drying to the inside should ever be required. Then drywall, obviously.

I gained 1.5 in in thickness towards the interior, but I now have a high-performing wall assembly with a nominal R value of 24 (which translates to perhaps R-20 actual performance when the framing members are included).
Prior to that, shoddily installed R11 paper-encased mineral wool batts were in the cavities, with plenty of air leakage due to gaps in the siding. Plenty cold and uncomfortable in the winter, with an actual performance of much less than their rating.

Next is the window. Looking forward to more comfort in this room!