Insulating a brick veneer house
I’ve currently gutted the living room in my 1950s brick veneer house back to the studs and am trying to come up with the best way to re insulate it. Details about the house from outside-in, brick veneer, air space of 1 inch with some motor droppings, some kind of fiber board (maybe water resistant coating on outside, but can’t tell). The brick is open on the top but has no weep holes. There are some holes in the fiberboard to the inside of the house, I’m guessing to facilitate drying. I’d be patching those before insulating. There is no metal flashing around the windows or on top of the foundation. There’s also about a 2′ roof overhang on all sides of the house.
I’d like to use dense pack cellulose in the 2 x 4 walls with intello plus as the air barrier, but I’m concerned about moisture accumulating on the fiberboard. Any suggestions on the best way to re insulate without creating more problems? I also have a brick fireplace on the exterior wall. Is the best way to air seal that with high temp caulk? Any help is appreciated!
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Betina,
In most cases, following your plan -- installing dense-packed cellulose between the studs, along with an interior air barrier and (possibly) a smart vapor retarder -- is a good way to go. Because this type of wall assembly has a high risk of inward solar vapor drive, it's important that you not include any interior polyethylene.
To improve the performance of this wall, you might want to hire a mason to drill weep holes through the vertical mortar joints near the base of the wall. Although the original masons didn't include weep holes (or the flashing usually associated with weep holes), these retrofitted openings will improve the rate of ventilation drying in the air space between your wall sheathing and the bricks.
What is the location/climate zone of this house?
The biggest air leak on an exterior fireplace is the flue. The typical firebox flap dampers are far from air tight. Gasketed chimney-top dampers are much tighter, but better still would be a wood burning fireplace insert, which would raise the amount of heat you get out of a cord of wood considerably. An exterior fire place is essentially energy-negative when burning wood, due to the high air infiltraion drive and the severe losses out of the back side of the uninsulated chimney.
It's possible to insulate the chimney on the exterior, but is a significant project, with lots of ways to screw it up, and is sometimes hard to make it look "architecturally appropriate".
It's in Wisconsin, zone 6. I am planning on installing a wood burning fireplace insert.
Thanks for the replies! Would there be any considerable down sides to using mineral wool batts over the dense pack? I'm considering the mineral wool because it would make the install much easier.
Asphalted fiberboard is fairly vapor-open (~15 perms in high humidity envioronment), and is moisture tolerant, not usually an problem for wintertime moisture drives. It's usually black (from the infused asphalt) on both sides, but sometimes only on the side facing the exterior.
In zone 6 you'll definitely need the "smart" air barrier/ vapor retarder such as Intello Plus on the interior side under the wallboard for wintertime moisture drive management, even WITH the high vapor permeance of the fiberboard sheathing. (In zone 5 and lower you can skip the interior side vapor retarders)
You could also get by with air-tight wallboard and half-perm paint (aka "vapor barrier latex primer), but that's more likely to be a problem for summertime moisture drives of sun-on-dew-soaked-masonry.
Certainteed MemBrain (2-mil nylon) is cheaper than Intello and more vapor open, (while still vapor tight when it needs to be), but isn't rugged enough to use as the blowing mesh. If dense packing it's probably cheaper to go with Intello rather than MemBrain + mesh.
For the enhanced resilience it provides it's definitely worth venting the brick veneer both at the top and bottom, even if it didn't originally have weep holes. Having a convection path between the brick and fiberboard will keep the brick and the fiberboard drier, which in turn will keep the moisture susceptible studs & cellulose drier.
We were posting at the same time...
Dense packing is great, since it it finds and partially seals any air-leaks by plugging them with fiber, and it fills completely, with no compressions or voids, and no paths for air to convect around the insulation the way it can with an ill-fitted batts. But it's still possible to do a reasonable job with batts.
If you're going to use batts instead of dense pack you'll need to caulk the framing to the fiberboard all the way around inside each stud bay first, and between the doubled-up top plates, as well as where the bottom plate meets the subfloor, and use can-foam to seal all the electrical & plumbing penetrations of the framing (including each stud where a wiring run passes through. It takes attention to detail to sculpt the batts to fit to near-perfection, but it's possible to do a good job if you take the time. Tuck every edge and corner in to ensure there aren't air gaps where the fiber meets the sheathing, then gently tug them out so that it'll be a compression fit.
Since it won't need to withstand the back pressure of a dense packing blower, you can safely use (much cheaper) MemBrain instead of Intello as the interior side vapor retarder.
Thanks Dana. Sounds like all things considered the dense pack may be easier. I'd like to do the install myself. Is there a big learning curve to getting the right density of cellulose?
Betina,
In general, it's tricky (but not impossible) to get the density you need with a low-power rental machine. It's much easier with the type of blower used by professional installers.
Here is a link to an article with more information: How to Install Cellulose Insulation.