Missing tar paper on brick exterior/wood stud house?
I own a 1922 brick bungalow in Illinois. The main floor has one wythe of brick on the exterior, then an 1 1/2″ air gap, then wood stud walls. I want to drywall the ceiling and walls in one room — the previous homeowners removed the original plaster and lath and added fiberglass insulation and drywall, which I removed. There is tar paper attached to the studs only on the bottom third of the wall (photo attached). After reading through several other posts here, I’ve decided not to insulate this room at all because I don’t want to somehow damage the brick over time (I’m also on a budget and doing many other repairs to the house that are more important). I was just going to drywall over the studs as is, but now I’m wondering if I should somehow correct the lack of tar paper on the rest of the wall.
When I removed the fiberglass insulation and drywall, which I would guess had been there for minimum 20 years, probably more like 30, nothing appeared to be wet or moldy. This house has 2′ overhangs everywhere and the brick seems to be in relatively good shape.
Would it be a problem to drywall over the studs as is, or is there a chance of a moisture problem? What might I do to correct that? Thanks for any advice.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
I'm not sure how you figure insulating between the studs would somehow damage the brick?
Drywalling it up as-is won't damage the brick, but you're more likely to get condensation & potentially mold growth in the drywall itself. Without a weather resistant barrier between the brick and the wallboard, the wallboard is even susceptible to bulk waterwetting from the exterior.
And closing it in without insulating would be a crime against the planet if this is heated space, and would likely rise to the level of a building code violation.
The 1.5" air gap is a "rainscreen" that limit's moisture transfer between the interior & exterior. The tarpaper has almost no function here, but I'm guessing that it is being used as the drain plane for the window flashing. You can probably figure out if that's the case by feeling around the edge of the window, or with a borehole camera flexed to get a better view. A full length properly-lapped tar paper could constitute a more proper weather resistant barrier/drain-plane, but that may be impossible to retrofit.
Before you do anything to it, take a look at the brick ties, and replace as-needed. Corroded brick ties are probably the biggest existential threat to the brick.
You can probably execute a reasonable exterior side air-barrier with housewrap pushed back to within a half-inch of the exterior edge of the studs, side-stapling it to the framing as you go. Better yet, a cut'n' cobble approach to 1.5" foil faced polyiso foam between the studs, held off from the brick with chunks of 1.5" foam as stand-offs, sealed to the framing with can-foam would put a weather resistant vapor retarder between the stud cavities and the brick, and would allow you to insulate the cavites with blown fiber or installing (even if you have to compress them) unfaced R13s, which would perform about 2x as well as the batts you took out, since there was previously no exterior air barrier to prevent convective loss of performance at the temperature extremes.
The details of how to really do it and get it right would probably require a site visit to inspect a myriad of detials, but this IS something that can be insulated, even if you went with 1.5" of closed cell spray foam on the brick, which would perform about as well as the better cavity fill. Depending on the rest that may even be the most-advisable approach (though a bit expensive at $1.50 per square foot), but the window flashing details may need to be amended.
There is false economy in skipping the insulation altogether, since once you close it in with drywall insulating it in the future would require guttgin it again. Energy isn't likely to become a whole lot cheaper in the future, and heating/cooling a room with ~R1 walls isn't cheap even at today's energy prices.
Thanks for the detailed response. The damage to the bricks I was referring to was reducing/eliminating the warm air passing through them to help dry them out if they're wet -- based on other things I have read online. Though again, it seems like the bricks are in good condition and that water is going where it is supposed to, and the bricks are not load bearing. I have worked on many houses before but never with brick, so it's been a learning experience.
I am uneasy about not insulating it, too. I had read about closed-cell spray foam insulation elsewhere on this site. Are there any big drawbacks or risks with this type of insulation? I just don't want to do something that will cause problems years down the road -- and I would definitely rather insulate than not (though I'm pretty sure this would be the only insulated room in the house...).
Thanks again!
Bricks tolerate moisture well, unless saturated during freeze/thaw cycles. In winter that "warm air passing through them" from the interior would actually ADD moisture to the brick at the spalling susceptible cold exterior surface. At a minimum you'd want at least some sort of interior vapor retarder to limit moisture drives, but air-sealing the interior would be critical.
Most brick veneer designs are vented at the top- either the cavity is open to the attic or eaves, or with slot-venting to the exterior in the vertical mortar every few bricks, and with weep-holes in the bottom course mortar every few bricks, which directs bulk water to the exterior via the weeps, and convective drying of the cavity via weeps and top vents. If those drying paths aren't already there, they can be added or modified to work better.
The decision to go with closed cell directly on the brick isn't risk-free, and really needs a site visit to see if that would work. The 2 foot overhangs works in your favor here, since it limits the bulk-wetting of the exterior, lowering the amount of drying capacity required, but the flashing details need to work right too. A local expert who can actually visit & inspect might be able to advise you better on that.
If that would truly the only insulated room in the house, there may be even be subsidy money for doing something serious. In some instances non-expanding injection foams filling the vent cavity can be used, others not. Again, construction details matter.
The fact that the batts you pulled out showed no signs of moisture damage means the cavity has sufficient drying capacity as-is, so at the very least a batt solution won't harm, if done reasonably. The pain-in-butt part will getting a proper air-barrier at the exterior. If you use housewrap for the air barrier rather than rigid foam, rock wool is probably a better choice than fiberglass, since it's denser- more air retardent, and completely fireproof. If the air-barrier is rigid foam and you need to compress the batt very much, fiberglass is easier to install.