Subfloor cavity question: Method in the madness?
Just posted this morning about a bathroom remodel I’m doing. Got some great feedback. Thanks much. Now I’ve encountered a different problem, and I didn’t know if I should tack it on to my previous question or just post separately. I’ve obviously opted for the latter.
My situation: When I gutted my bathroom last week, I came across an interesting anomaly when I tore up the subfloor and underlayment. Found a 3″ round galvanized a.c. supply pipe running between the joists about half-way across the room (see attached pic), uncapped and blowing cold air into the subfloor cavity below the bathroom. The 3″ duct pipe came from the same plenum as the bathroom register duct, the latter of which was triple the size of my mysterious pipe and fully operational.
My Q: What to make of this uncapped a.c. supply? Only thing I can think of is that the builders originally intended it to supply nominal airflow into the large bathroom subfloor cavity, which seems to serve as a hub cavity of sorts, housing water lines, pipes, the underside of the tub (and its exposed fiberglass insulation), an empty lower cavity in one of the bathroom’s interior wall that feeds into the attic, and finally, the open header cavities of two separate downstairs interior walls. Just wondering if the intention was for the line to cool the cavity in the summer and heat it in the winter (to keep pipes from freezing, to help warm the tub (which rests over eaves), and to move air through the lower interior walls. I have no idea. All I know is that I pulled the pipe away from the starting collar at the plenum and capped it, as I’ve always thought that the idea behind insulating a house was to STOP airflow in all of its under-floor cavities and crawl-spaces. To this end, I’ve been blocking off access to the attic from the interior wall, blocking off the open headers to the downstairs interior walls, and sealing off the insulation in the underside of the tub from the rest of the cavity.
But now I’m left wondering if it’s a good thing to create a subfloor cavity space that will essentially have no air-flow at all. Is this a good thing in an old house? Or do subfloor cavities need to “breathe”?
Anyhoo, would love to hear your thoughts on this pipe and the odd subfloor cavity that it’s supplying air to (pics attached).
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