Renovating solid brick walls in Florida
Hello everyone,
First off, keep in mind I’m in Florida.
I am fixing my roof eaves and decided to work on the inside of the exterior walls. I have solid brick walls. No air gap, just one layer thick. The old walls simply had heartwood nailed straight on the brick and then Birch paneling…that’s it. Simple enough, right? However, over the corse of 50 years and
neglect, termites ate a lot of that wood. They came uo next to the brick.
Now, the code in my area requires I insulate when redoing the walls. The main two systems are a 2×4 wall next to the brick wall with Batts OR polycianorate foil insulation against the brick with furring over that….both followed by drywall. It’s also advised not to do poly. I don’t like either system
My plan…put a continuous layer of foil insulation against brick using a 1×6 pt board as a bottom seal(termite precautions). Then build a metal stud wall then drywall….does this sound reasonable? I want as much fire and termite resistance as possible.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Sorry, zone 2A
Shakey,
I don't know what you mean by "foil insulation." Do you mean:
1. Foil-faced polyisocyanurate?
2. A radiant barrier?
3. Foil-faced bubble wrap?
If you mean foil-faced polyiso, your plan is a good one.
If you mean a radiant barrier or foil-faced bubble wrap, your plan is a bad one. Neither a radiant barrier nor foil-faced bubble wrap have significant R-value, so these material aren't insulation.
From "...polycianorate foil insulation..." in the prior paragraph I would infer:
>1. Foil-faced polyisocyanurate
Could be wrong.
The performance of a continuous radiant barrier 1.5" of dead air space on each side and foil-backed wallboard facing it can be as high as R3-R4 but that's woefully shy of code min. If you stacked 2-3 layers of radiant barriers with 1" air gaps you might get there, but not if the steel studs/furring is thermally bridging it.
I'm not sure how effective pressure treated lumber is as a termite barrier. Copper clad foundation sill gasket material (eg Mite-Out ® ) would probably be cheaper and more effective, as would galvanized steel framing channel. Since you're using steel framing, why use any wood at all?
Steel furring would use up less internal space than steel studs but make it hard to deal with electrical boxes & wiring, etc. but there are ~1.5" deep steel stud options with sufficient depth for shallow electrical boxes.
Since fire resistance is a priority, installing rock wool in the steel stud cavities would offer considerable fire resistance while improving the thermal performance somewhat. Empty stud bays allow flames from burning paper facers on wallboard to spread. If the cavities are to be left empty, use foil backed wallboard for the enhanced fire safety.
Fire rated polyisocyanurate (eg Dow Thermax) takes a long time to light-off (if a bit quicker than your pressure treated bottom plate), and is a lot simpler to assemble than stacked radiant barriers. An inch of continuous polyiso (no thermally bridging studs) on the interior would hit code min for masonry walls in zone 2 on it's own. The additional R0.5-R1 you would get from foil backed gypsum board mounted on steel furring would be gravy.
Okay...bear with me....had a lot to say and it all just got deleted so here it goes again somewhat discombobulated.
First off, yes Martin I was referring to polyisocyanurate and not bubble roll.
I had a good plan but am very indecisive so now Dana has made some points that I have to ask about beginning with the polyisocyanurate. I just went by HD and they only carry 3/4 and 1 inch in my store (you can order thicker). The 1 inch has an R value of 5.9 to 6.0. I'm guessing you were referring to 3/4 in the first paragraph, which was my plan. At the end you spoke of a continuous radiant barrier working at 1 inch without thermal bridging So basically make sure I have 1 inch or greater polyisocyanurate withoit thermal bridging?
Next, the primary reason for the PT bottom plate was actually thermal bridging. I do not want any 'foam touching concrete floor'. So I thought it would be better to have the PT as a solid piece under the whole wall versus metal. I could always go metal....or even PT with a small termite sill like you mentioned....not sure the best way here?
As far as the steel, my plan was to have steel studs (drywall side) attached to the floor and ceiling and never actually touch the polyisocyanurate or brick wall. Definitely want plenty of room for outlet boxes, the full 3 1/2. I could probably put metal furring on the brick to glue the polyisocyanurate for a better attachment. I am willing to come in about 6 inches....space isn't that important compared to other things.
I looked up the rock wool and it looks like a nice option. Would it be better than the polyisocyanurate? I read the wool is virtually fireproof...but how is it attached with metal studs, etc. Is it like batt insulation? We're you saying rock wool in place of polyisocyanurate or in addition? The polyisocyanurate I have a available at HD has a high fire rating as well.
I looked up that foil faces gypsum....looks awesome.
So.....all these options makes things more confusing (in a good way). I am doing one room at a time so it would be in budget to do most any combination. I could do the polyisocyanurate leave a gap and then the rock wool....will all those work together as one system or is just the polyisocyanurate sufficient as originally stated. I Have to do an owner builder permit (it's going to be a little while) and I can imagine the inspector looking at my plans, lol.
Shakey,
As you point out, 1 inch of polyiso has an R-value of R-5.9 or R-6.0. In Climate Zone 2, most building inspectors will let you get away with wall insulation as low as R-6, assuming you are insulating the interior of a so-called "mass wall" with continuous insulation -- so you can probably do that according to the code. But it isn't much R-value.
You wrote, "I am willing to come in about 6 inches....space isn't that important compared to other things."
If that's how you feel, you might consider installing somewhat thicker rigid foam. After all, you only get a chance to do this job once.
Shakey,
Q. "You spoke of a continuous radiant barrier working at 1 inch without thermal bridging. So basically make sure I have 1 inch or greater polyisocyanurate without thermal bridging?"
A. Either continuous insulation or a radiant barrier adjacent to an air space can reduce thermal bridging through framing members like studs or plates. But the thermal bridging can't be eliminated -- it can simply be mitigated. In all cases, continuous insulation is better than insulation installed between framing members like studs.
The PT sill won't provide any meaningful termite protection. The termites will still easily find gaps in the system to get up into the walls. PT is required anyhow because it is in contact with damp masonry. Steel would also work, as suggested. I'd also note that termites love to eat the paper facing on drywall. Foil-faced drywall won't be eaten, but termites will still eat the paper side facing the living space, behind the paint. Treat the termites and use a baiting system. This will at least reduce the pressure.