# Bathroom exhaust fan is causing ice dam



## Windows on Wash (Aug 30, 2011)

Air Seal the penetration and insulated the pipe.


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## SeniorSitizen (Sep 10, 2012)

sbkim said:


> What can I do about this. Thank you


You can change the fan discharge location to the soffits where they should have been located originally.


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## Windows on Wash (Aug 30, 2011)

Fairview said:


> You can change the fan discharge location to the soffits where they should have been located originally.


I don't care for soffit discharge myself. It is nice to be able to bury the line in insulation but I prefer through the side of the home as compared to a soffit discharge where more of the warm air just percolates right back into the attic as most of them are installed.


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## sbkim (Apr 30, 2012)

Windows on Wash said:


> Air Seal the penetration and insulated the pipe.


Assuming it's properly insulated etc, wouldn't the warm discharge air alone cause the ice to melt and potentially cause ice dam. I presume the best way is to discharge to the side.


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## Windows on Wash (Aug 30, 2011)

Small amount of melt on the roof side from the warm air will create some melting but not usually enough to create and ice dam.

Side discharge is my preferred as well but the small square footage of snow melt is minimal. The warm air does rise pretty quickly.


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## sbkim (Apr 30, 2012)

Thank you windows on wash... I will double check insulation around this area first and go from there.


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## ParagonEx (Sep 14, 2011)

Nearly all bathrooms here are vented using that exact same bathroom vent and this is actually the first time I have heard of this creating an ice dam.


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## SeniorSitizen (Sep 10, 2012)

This is another example of the misconception that all ice dams that put water into the walls and dripping from windows have a large accumulation of ice on the eaves of a roof.


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## hammerlane (Oct 6, 2011)

Fairview said:


> You can change the fan discharge location to the soffits where they should have been located originally.


Disagree. I prefer side wall discharge or roof discharge. Coming out of the soffits, you are pumping it down, where the warmer less dense air now wants to rise. Where will some of it rise to? Possibly back into the attic thru the soffit especially if you have continuous soffit venting.

I had three bath vents discharging into the soffit areas in the attic when we moved into house. I promptly changed them to roof vents which appear to be the same ones that the poster use.

I have no issues with ice dams though.


Here is a video that may be of interest regarding soffit venting:
https://www.youtube.com/watch?v=K3vM4i31Y40


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## sbkim (Apr 30, 2012)

Thanks again for the replies. I thought pictures are worth thousand words. Here's a few picts of the area in question and resulting ice dam. Water must have bypassed the water/ice shield and entered through the side walls...


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## hammerlane (Oct 6, 2011)

In my opinion the exhaust vents have nothing to do with ice dams but the geometry of the roof is something to consider.


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## sbkim (Apr 30, 2012)

Thank you hammerlane. I presume geometry is something that won't be easy to change but would appreciate any other thoughts. 

Do I need another downspout a the corner where the ice built up was?

Did someone improperly install ice/water guard for water to enter the side of my wall (where the windows are)?


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## IslandGuy (Jan 30, 2014)

IMHO your exhaust fans have NOTHING to do with that ice dam - that's a result of the snow getting so thick that it traps the sunlight that penetrates it, causing the lower layer of snow to melt, which promptly re-freezes when it drips out into the gutters. This process continues over and over again, all day and day after day. The way all 3 roofs converge into that tiny valley is pretty from the street, but impractical in a northern climate.


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## sbkim (Apr 30, 2012)

You guys are amazing. I got the same confirmation from my builder. Looks like perhaps installing roof heating element is the best way to address this matter... By the way, I am in Chicago and didn't realize how cold it gets here after being here for only two warm winters.


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## Windows on Wash (Aug 30, 2011)

hammerlane said:


> In my opinion the exhaust vents have nothing to do with ice dams but the geometry of the roof is something to consider.





IslandGuy said:


> IMHO your exhaust fans have NOTHING to do with that ice dam - that's a result of the snow getting so thick that it traps the sunlight that penetrates it, causing the lower layer of snow to melt, which promptly re-freezes when it drips out into the gutters. This process continues over and over again, all day and day after day. The way all 3 roofs converge into that tiny valley is pretty from the street, but impractical in a northern climate.


Hammer and Island nailed it.

Nothing about the vents specifically that are creating that issue. 

That being said, the plumbing vents, bath vents, skylight, and general high level of penetrations in that valley area are not helping your general predicament. Air seal and insulate all those penetrations and it will help.

All things being equal, you are going to have issues with that area in the future and I hope they did that whole area in Ice/Water.


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## sbkim (Apr 30, 2012)

Yes, to my knowledge they installed ice/water. I do have a room with tall ceiling that follows the pitch of the roof so I need to make sure we have adequate insulation. Thanks


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## GTAC (Jun 3, 2021)

Reviving an old post here...

So I had a new roof installation on the house last fall. The installer convinced me to move the 2 bath vents from the soffits to small, low-profile style roof vents. At the time I raised the concern of issues with the vents getting covered with snow as we live in Michigan. I was assured the vents were "code" and there would be no issues.
Fast-forward a few months and after a few heavy snowfalls. As I was in the yard I looked toward the back of the house and noticed 2 very large ice dams directly below the vents. No issues on any other part of the roof as we are heavily insulated and properly vented in the attic spaces. This includes soffit vents with baffles properly installed and new ridge vents at the peak of the roofline.

There is zero doubt in my mind what has happened. Snow encapsulated the vents. At the point the vents were used the warm, moist air vented into the accumulated snow on the roof covering the vents. It was warm enough to melt a cavity in this snow but not enough to actually break through the pile. The melted snow drained straight down the roof until it hit the gutters and froze there. Gradually it backed up the roof a ways and also over the gutters creating rather large pillars of ice.
The pitch of my roof is adequate and should not be considered part of the issue. (not sure the exact pitch offhand)
Insulation is more than adequate.
The vents are roughly 3 feet from up the edge of the roof/gutter.
The roofing and vents themselves appear to have been installed properly. I think its the STYLE of vent that is not working here. Gable venting would be difficult for 1 of the vents and almost impossible.

My ultimate questions are:

1. What are my options to remedy this before next winter creates the same issues with possible COSTLY damage? (My only thought is a different "stack" style vent)
2. Shouldnt this be remedied by the installer since the exact concern I expressed was encountered on the very first winter?

Thanks for any input!


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## Exhausted repairs (4 mo ago)

GTAC said:


> Reviving an old post here...
> 
> So I had a new roof installation on the house last fall. The installer convinced me to move the 2 bath vents from the soffits to small, low-profile style roof vents. At the time I raised the concern of issues with the vents getting covered with snow as we live in Michigan. I was assured the vents were "code" and there would be no issues.
> Fast-forward a few months and after a few heavy snowfalls. As I was in the yard I looked toward the back of the house and noticed 2 very large ice dams directly below the vents. No issues on any other part of the roof as we are heavily insulated and properly vented in the attic spaces. This includes soffit vents with baffles properly installed and new ridge vents at the peak of the roofline.
> ...


Did you ever figure this out? I have been dealing with ice dam prevention on my house for 14 years, mainly by removing the snow. I have tried insulation and adding passive vents. My problem is a little different, but here are my two cents.
1.) If possible install the bathroom vents on the south facing part of the roof. Ice dams usually don't form on that side as it get plenty of sun (unless you have shading). I heard someone on another forum say you can use a candy cane style vent (never seen one myself).
2.) I assume this was not an option as it's very difficult to get construction folks to come remedy problems.

I am amazed how little information is available on details of this problem, yet it is so common in northern climates. The last resort always ends up being heat cables. It's frustrating we seal up our homes for energy efficiency and then we heat the exterior roof.


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