Should I vent bath fan through roof, or soffit?

db4570June 18, 2010

I am getting a new roof installed (and tear-off and likely a lot of plywood), and am simultaneously getting a new bath vent fan. I have gotten mixed opinions on whether to vent the new fan through the roof or through the soffit (eave). The roof contractor recommends the soffit, to minimize protrusions through the roof. But others have said it will flow better with minimal condensation issues if we go up through the roof.

The house is an early 70's ranch in the cold, wet Northeast.

What are the pluses and minuses of each? Help appreciaated!

Thanks,

David

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metaxa

Go through the roof.
Properly installed, the roof vent will be no issue at all.
The moisture laden air simply moves away, into the atmosphere.

Coming out of the soffits, you are pumping it down, where it now wants to rise. Back into the soffit.

Protrusions through the roof? Well you have the vents for your plumbing, at least two I'd expect. A chimney comes either through or alongside. Your roof vents or ridge vent also are there.

What is one more, if they are all installed and flashed and such properly?

    Bookmark   June 18, 2010 at 1:01AM
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macv

If the roof pitch is low I would vote for the soffit if there is no eave vent nearby.

    Bookmark   June 18, 2010 at 8:18AM
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drywall_diy_guy

I have mine through the roof. Just get a kit, follow the instructions, and install using a "shingled" method so the top flashing sits under the shingle up from it and the bottom flashing sits over the shingle below it. Seal up good with roofing cement. Lots of snow here and no problems in 3+ years.

    Bookmark   June 18, 2010 at 9:27AM
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metaxa

No offense, drywall diy guy, but roofing cement is the last thing you want on a roof vent. It holds water in, you want it to drain away.

Installed correctly there is no need for any cement, caulk, goop, whatever.

On a roof, its not if its going to leak, it is when its going to leak. You don't want to hasten that happening. Let it drain.

    Bookmark   June 19, 2010 at 12:43AM
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manhattan42

For the best results, the vent should terminate through a gable wall of the roof assembly for best results.

Vent terminations through roofs or soffits should be avoided whenever possible.

    Bookmark   June 19, 2010 at 6:02AM
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drywall_diy_guy

The video I watched when I did this is at the link below. I used the roof cement over the exposed nails. The video recommended caulk however.

Here is a link that might be useful: Bathroom Roof Vent

    Bookmark   June 19, 2010 at 9:13AM
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metaxa

For the best results, the vent should terminate through a gable wall of the roof assembly...

Again, no offense meant but "best" results would be a continuous ridge vent, no? Vents placed on gable ends don't work very well unless they are powered.

And a proper roof vent doesn't require any visible nails.
Stop buying them off the shelf at a big box store and go to a proper roofing supply, spend a couple of dollars more for the right stuff. Its no wonder folks complain about leaky roofs all the time!

And while I'm at it (lol), venting a roof is a lot more than slapping some vents into the roof, you really should calculate soffit area, attic volume, etc. I bet only one in ten roofers know how and of those I bet only one in ten actually does it.

The difference in a standard, stick built home with and without properly spec'd and sized AND installed roof venting is huge.

Roof keeps everything else dry, roof venting keeps everything else livable. And makes your roof last longer. My advice to the OP is do it right, find a someone in real life who will do the calculations, fix the soffits, the baffled airway, the ratio of soffit to vent space, install the proper vents in the proper manner (hint: they won't be plastic) and willingly help you become aware of the how and why.

Or not.

    Bookmark   June 20, 2010 at 3:53AM
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manhattan42

"Again, no offense meant but "best" results would be a continuous ridge vent, no? Vents placed on gable ends don't work very well unless they are powered."

Huh?

We are talking about bath fan vent termination locations, not attic vent locations....

    Bookmark   June 20, 2010 at 7:39AM
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metaxa

So right, sorry, my mind switched from bath fan to just roof vents in general.

A powered gable vent, venting a bath or kitchen fan would be just fine.

    Bookmark   June 20, 2010 at 5:24PM
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energy_rater_la

Oh no!!..lets not do the pav thing!
not again

    Bookmark   June 21, 2010 at 9:51AM
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sofaspud

Whichever way you decide, make sure the vent fan has enough HP to actually vent the air. If the line run is long and you have a small unit, it won't vent properly, especially if you go straight up through the roof and you have big attic. I wouldn't assume whoever's doing this for you calculates it right. Also, unless you specify, you're probably going to get the cheapest fan the guy can get.

FWIW, I recently replaced both my bath fans with Panasonic units. These are expensive, but they are good quality and very quiet.

    Bookmark   June 21, 2010 at 4:49PM
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db4570

The Panasonic is actually what I bought. I am going to have the roofer install the vent outlet directly overhead.

Thanks for the replies!

David

    Bookmark   June 25, 2010 at 8:39AM
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lostinit

Never vent through a soffit. This is common sense/roofing 101. Anyone who tells you different is either a fool or a liar.

If you push warm/humid air through the soffit, it will just get sucked back into the attic and lead to other problems like mildew. Going through the roof guarantees it will go up in the air and away from your home.

    Bookmark   June 28, 2010 at 2:24AM
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totsuka

When I put in a new exhaust fan in our bathroom the builder never put any exhaust to the roof. It was just venting into the attic. (Florida home)- 30 years!. I did not want to punch a hole into the roof so I ran the exhaust over to the soffit and installed it there with a vent. HD and Lowes sell soffit vents. To me, I did not want another hole in my roof but to each their own.

    Bookmark   September 6, 2010 at 6:41PM
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susanelewis

Panasonic install directions are clear that their exhaust fans (at least my Whisper Warm) are to be vented out the roof. I gave the instructions to my Solatube guy and while he was installing the tubes he vented my Panasonic for me. There must be a reason that Panasonic advises this. They don't provide any parts for it so it's not like they are making money on what type of method they are recommending.

    Bookmark   September 9, 2010 at 1:09PM
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JP_JP_com

Which ever is the shortest run.

    Bookmark   May 30, 2011 at 2:03AM
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frmrnyker

I have to chime in here for some advice for my upcoming bathroom reno.. I will be taking a "shower room" and "half bath" to two full baths.

I have a hip roof, 2 story colonial style home. Currently there is no venting as there has been no "real" updates done. The multiple prior owners did some not so great redecorating etc but never installed exhaust or plumbing vents.

As I will have all of the walls open, I am planning on fixing this. My problem lies in that I've spoken to several carpenters - all differ in what to do. Two turned down the job based on the height and pitch of the roof, stating that they did "not want to be up that high" - granted the roof is quite high - equiv to a 3 story due to the basement being a walk out etc.

So the two that agreed to take the job (havent decided on either one yet) say to vent to the soffit - given my roof there is plenty of overhang. I also live in Maine - my roof spends the winter fully covered in snow.

please advise....

    Bookmark   July 13, 2011 at 2:45PM
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fromtheqc

lostinit - why get insulting?

The relocation company that bought my house for a move with a Fortune500 company required me to vent my fan through the soffit. Because it is building code in some cities, I had to meet their "uniform standard" of strictest standards. Therefore, if it is building code in some places, it must not be common sense 101. Their explanation, because vented through the roof results in leaks.

    Bookmark   June 19, 2014 at 8:10PM
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annkh_nd

qc, this is a really old thread - lostinit might not see your reply.

I'm afraid I agree with him/her, however. The explanation was included in the post: "If you push warm/humid air through the soffit, it will just get sucked back into the attic and lead to other problems like mildew. Going through the roof guarantees it will go up in the air and away from your home."

I would love to see a copy of the building code that suggests venting a bathroom fan through the soffit is recommended.

The alternative to a roof exhaust (if you're concerned about not being able to seal the hole in the roof) is to exhaust through a gable end. Just make sure that there is a slight slope to the outside, so and condensation in the duct will end up outside. And, as someone else pointed out, make sure the fan is powerful enough to do the job. Longer runs require more power.

    Bookmark   June 20, 2014 at 3:31PM
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