One of the things I worked on with Dean the night before spray foam was the bath fan exhaust ducts. Historically, these are installed using regular 3-4″ metal ducting, but it can leak steamy air into the ceiling assembly. Because the metal conducts the heat and cold from outside, it can also condense on the outside of the duct if it’s not insulated. Both of these can cause mold within your walls or attic. While you can seal the duct joints and insulate it, a simpler and cheaper solution is to use PVC pipe and slope it to the outside. It won’t leak, and moisture will drain to the outside, and the plastic generally won’t condense water on it.
I used regular 4″ schedule 40 PVC to do the basement bathroom and found that the challenge was the connections on either end, both to the fan as well as the exterior vent cap. Because both are 4″ in diameter, neither fits inside the other easily. For a number of years I just had a drain cap on the end of it, but Dean has a metal crimper and helped me get a proper vent cap onto it.
For the rest of the house, I learned my lesson and switched to drain and sewer PVC. This thinner walled pipe is what we used for our drainage project, before which I wasn’t really familiar with it. Because the pipe is frequently used in long runs, each 10′ pipe has a flared end to allow connecting one to the next. It just so happens this flared end fits the vent caps perfectly, and the thin wall of the straight end fit to the bath fans just fine too. You can glue it up just like regular PVC and then seal the connections at each end with caulk.
Before the siding went on, Dean brought over his hole saw kit and helped me drill holes in the exterior wall as well as holes in some blocks of wood and rigid foam insulation to attach to the outside of the house so that the holes would be flush with the exterior foam. The powder room and main bath were simple straight runs, so installing the pipe and caulking the ends was a matter of twenty minutes on the ladder. The master bath, on the other hand, was a bit of a challenge. Like the others, I’d cut the exterior hole in the wall to be a straight shot from the fan, about five feet long.
Unfortunately, the electrician wanted to put the ceiling light in the center of the shower, which I agreed would look nice, which meant the fan exhaust would need to zig zag around the can light. Not the end of the world, but then the plumbers ran the overhead shower through that same space, after I asked them not to, and the run would have to jog up and then back down, which could lead to condensation pooling instead of draining. The next time they were out I asked them to move it, which (after some grumbling) they did, so I finally got this last run installed.
We’re working on batted insulation in interior walls and ceilings for sound and fire block, HVAC work has finally started, and I’m wrapping up the wiring for the security system, so I should have some additional posts soon.
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