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Unread 10-29-2015, 07:00 PM   #1
Tiger Mountain Tile Inc
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Building insulation/ventilation question

I started a remodel and am getting the shower ready for the plumber to come in. I removed a chunk of the subfloor around the drain and there's no insulation and there's air coming in through the vents below.

Is it supposed to be like this? Are there supposed to be baffles or something so you can also install insulation?

The backwall is an exterior wall. This is the second story of a townhome. The perforations you see below the drain is the vent that I'm referring to.

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Unread 10-29-2015, 07:15 PM   #2
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Are those vents open into the ceiling of the occupied space below, Jim?
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Unread 10-29-2015, 07:19 PM   #3
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No. I think it cantilevers out and you're looking at the outside right there. The 2x6 block that is in the nearside of the opening is holding back insulation.
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Unread 10-29-2015, 08:07 PM   #4
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OK, thoroughly confused here. You say "back wall" is exterior wall. Where is this back wall in your photo?
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Unread 10-29-2015, 09:30 PM   #5
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Maybe this photo will help. The back wall is the top of the photo. The drain is directly above the exterior. The back half of the shower is open below the joists.

I didn't remove any insulation.

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Unread 10-29-2015, 09:31 PM   #6
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I'm guessing top of the picture. Looks like there's some insulation poking out near the floor.
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Unread 10-29-2015, 09:40 PM   #7
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Yes in principle that section of floor that is exposed to the outside should have insulation or there will be heat loss or gain into the structure from that section.

I would add insulation as part of your remodel.
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Unread 10-29-2015, 10:11 PM   #8
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My concern is the ventilation aspect of it. Without a better understanding of how the system works I'm reluctant to insulate it. I'm not really sure how the ventilation works and I definitely don't want to block it and cause mold.
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Unread 10-29-2015, 10:35 PM   #9
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'Fraid you've got me completely baffled on that one, Jim.

Can't imagine why they'd insulate the floor joist cavities over the occupied space (except for sound isolation) and leave the portion exposed to the outside ventilated and not insulated.

Doesn't compute with any of the building science I'm at all familiar with.
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Unread 10-29-2015, 10:51 PM   #10
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A cantilevered floor system over unconditioned space in your neck of the woods is typically not vented, and is insulated.

Insulation needs to be fitted tight to the underside of the subflooring to reduce condensation formation. So, if there's space under the insulation, baffle it or use those steel spikey things to hold the insulation up and leave space below for air movement. If there's no space below, don't worry about it.
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Unread 10-29-2015, 11:38 PM   #11
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What kind of ventilation system are we talking about?
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Unread 10-29-2015, 11:43 PM   #12
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Ravin

Like eave vents for a roof. Sounds like those cantilevered joists may align with adjacent rafters/trusses, and the siders just continued the eave vent even though it's not needed.
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Unread 10-30-2015, 06:48 AM   #13
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They never had an issues with the p trap freezing solid? I don't know why you wouldn't insulate the whole thing.
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Unread 10-30-2015, 12:53 PM   #14
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Hey Chuck / Mullet.

Please put your name back in your sig line for us. Make a new name up if you'd like. Thanks.
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Unread 10-30-2015, 04:51 PM   #15
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Here's some more photos:

The red area is the approximate location of the shower

Name:  2015-10-30 11.55.26.jpg
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And another photo that's a little closer in of the drain

Name:  2015-10-30 12.38.20.jpg
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