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Shower exhaust going into attic
Old 07-20-2015, 12:15 PM   #1
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Shower exhaust going into attic

I was up in the attic over the weekend and noticed that the exhaust fan from the upstairs shower is vented into the attic. I looked around, there's no sign of any water residue or damage. I thought all exhaust vents had to lead out through the roof or the side of the house, but not in this case.

How does one vent this once the house is built? Does a hole need to be cut in the attic and the shower vent connected to it? Any recommendations or helpful web sites would be appreciated.
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Old 07-20-2015, 12:19 PM   #2
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Unless you have a very small attic or use that shower fan far more than average I wouldn't worry about it. We have a large attic area and our fans vent only to the attic.
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Old 07-20-2015, 12:24 PM   #3
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^ so do ours
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Old 07-20-2015, 12:27 PM   #4
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Is this ? a fan forced exhaust, or just a passive screened opening to the attic. If the latter, was typical construction in the 20th century. No need to change it.

Poor practice , IMO, but I have seen a lot of bath exhaust fan ducts terminated in the attic, just under roof whirlly bird ventilators.
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Old 07-20-2015, 12:27 PM   #5
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How does one vent this once the house is built?
I've seen this before, and also with clothes dryers. It's not right for all kinds of reasons--it introduces moisture to the attic, it is a way for a lot of warm air to escape into the attic in the winter (24/7--it's a lot of heat loss) if there's no flapper, etc, etc. It's done this way by cheap builders or sometimes by re-roofers who don't want to bother with a boot/stack (the clue is the small hole in the roof deck that is just covered with tarpaper and shingles. "That oughta be okay").

The two proper options for venting are through the roof or with a soffit vent. A soffit vent is just an opening with a cover under the soffit of the roof (under the eaves). From a purely theoretical standpoint, the "through the roof" answer is slightly better, as the warm, moist air from the bathroom is then clear of the attic. Exhausting the air out the soffit means that some of it may come back in through the normal venting of the attic. From a practical standpoint, I like a soffit vent because it is one less hole in the roof to eventually leak.

In either case, you need a duct from the present duct to either the roof deck or out tot he soffit. In either case, insulate ALL the duct that comes into the attic, otherwise the cold attic (in winter) will condense a lot of moisture on the inside of the duct, and it will drip somewhere. If you go for the soffit vent, try for a short "up" length from the bathroom, and a longer sloping "down" length so any condensation will drip out the soffit and not back into your bathroom. Make sure you have a flapper somewhere int here (possibly already integral to your fan unit, but add one if not) to prevent the constant flow of conditioned air from your home into the attic--the flap opens only when the shower fan puts pressure into the line. Smooth duct will flow more air and trap less water than flex duct.

At a bare minimum, move the end of the shower vent duct to a location inside/under an existing roof vent, add insulation to the duct, and assure there's a flapper in there somewhere.

Good luck!
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Old 07-20-2015, 12:32 PM   #6
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If you have adequate ventilation, I wouldn't worry about it. The venting of bathrooms to the outside is a newer code requirement and many older houses are vented into the attic.
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Old 07-20-2015, 12:37 PM   #7
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That's how it was in my house too. I added a piece of duct to bring the exhaust closer to the nearest roof vent, just to be on the safe side. But it had been this way for many years and there was no trace of mold in the attic which was also thoroughly vented through the gables.
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Old 07-20-2015, 12:41 PM   #8
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I assume this is your Chicago area home?

At least some of the posters saying it's OK do not live in winter climates. They are probably not aware of the issues with warm moist air condensing in a cold attic.

Moisture in a cold attic can be a real problem, and it can get serious. I would get it properly vented.

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Old 07-20-2015, 12:43 PM   #9
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I'd be mildly concerned about a shower vent, but would NEVER vent a dryer into the attic...

Piercing the roof would be the ideal solution, but an eave, soffit, or ridge vent would be reasonable as well.
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Old 07-20-2015, 12:45 PM   #10
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+1

I know bupkis bout livin' in da cold...
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Old 07-20-2015, 01:14 PM   #11
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Yes, this is in Chicago, a cold weather climate, and I don't even know bubkis. No worries, all the know-how is right here on the forum.

This is an upstairs shower, the exhaust is a fan. It doesn't get much use during the cold months, so I probably could get by without doing anything, but I'd rather fix it - it the fix can be done by a handyman and not a roofer. My guess is that rules out a new vent in the roof.

That means my choices would be to install a soffit vent or extend the vent in the attic closer to the existing roof vent. In either case, following Samclem's helpful advice. Do I have it right?

And yes, the dryer vents outside - I am forever unclogging the screen.
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Old 07-20-2015, 01:33 PM   #12
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If you decide to go with a soffit vent, here's a product available at Menards that has the exterior grill and an included flapper/backdraft preventer. Less than $10 and you can paint it if you don't need/like white. I'd cut some screening and put it inside to keep out even smaller critters.

But you said "upstairs", so that means any soffit is 16-20' up. That's not fun. Going through the roof deck isn't as hard as it sounds, if you have "regular" asphalt shingles: Drill a big hole, jab a sabresaw through and cut the 4" hole, install the stack and boot slid under the shingles, and glop on a bunch of sealant. But, it is another hole.
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Old 07-20-2015, 01:59 PM   #13
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When I moved into my current house... The second floor had two bathrooms... the exhaust of the two bathrooms were connected to each other! I corrected that by connecting each through the roof.

If you live in the cold weather I would be especially cautious of venting to the attic, any added heat in the attic raises the possibility of ice dams.
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Old 07-20-2015, 02:16 PM   #14
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The key here is to have adequate attic ventilation. Without that and living in cold Chicago winters, you could have condensation issues. Of course that depends on the volume of attic vs the fan/moisture level/time running.

An attic with sufficient ventilation should not have any problems, although I do agree venting to outside is better.
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Old 07-20-2015, 02:24 PM   #15
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Yes, this is in Chicago, a cold weather climate, and I don't even know bubkis. No worries, all the know-how is right here on the forum.

This is an upstairs shower, the exhaust is a fan. It doesn't get much use during the cold months, so I probably could get by without doing anything, but I'd rather fix it - it the fix can be done by a handyman and not a roofer. My guess is that rules out a new vent in the roof.

That means my choices would be to install a soffit vent or extend the vent in the attic closer to the existing roof vent. In either case, following Samclem's helpful advice. Do I have it right?

And yes, the dryer vents outside - I am forever unclogging the screen.
If you do extend the vent, I would recommend using insulation around the duct. The first time I used my bathroom fan with uninsulated duct on a merely crisp Alabama morning, I was greeted with a rain shower in the bathroom as the steam had condensed in the duct and water was flowing back down. In Chicago, you probably hit those temperatures in September.
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Old 07-20-2015, 02:34 PM   #16
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I had the same problem with the vent over our kitchen range. I had a local remodeler come out and add a vent in the roof. They cut a hole in the roof and installed the vent with flapper I purchased on top of the roof. They sealed the vent with flapper and ran duct from the range vent in the attic to the new roof vent. You can install the roof vent through the existing shingles easily. I don't recall the exact cost. I think labor and material was less than $200. YMMV.
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Old 07-20-2015, 02:43 PM   #17
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how often do you use the exhaust fan in your upstairs shower?
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Old 07-20-2015, 02:48 PM   #18
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Our shower vent/exhaust fan just ends in the attic. I guess I'll put that on the list of things to worry about one day, maybe the next time we get a new roof, but so far no issues with it.
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Old 07-20-2015, 02:51 PM   #19
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how often do you use the exhaust fan in your upstairs shower?
It's of interest, but not the whole story. If there's no flapper/backdraft preventer, more moisture probably goes into the attic through normal stack effect of the inside air the other 23 hours per day than would go there from one wet bathroom. And then there's the heat loss issue, also dependant on a flapper valve.

With a two story, the heat loss through a 4" fan/vent will be larger than in a single story, due to the greater stack effect.
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Old 07-20-2015, 02:51 PM   #20
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If you do extend the vent, I would recommend using insulation around the duct. The first time I used my bathroom fan with uninsulated duct on a merely crisp Alabama morning, I was greeted with a rain shower in the bathroom as the steam had condensed in the duct and water was flowing back down. In Chicago, you probably hit those temperatures in September.
+1, in any cold-winter climate, the exhaust air needs to be ducted to the outside, and the duct needs to be insulated. An easy way to do that is buy some "flex" ducting to slip over your galvanized smooth ducting. 6" flex fits nicely over 4" round galvanized if put on prior to making the final end connection. It will compress easily in length, so put a few extra feet on and it will compress to fit.

eg: Atco Insulated Flexible Duct, Polyester, 180F 17002512 | Zoro.com
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