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I'm rebuilding a bathroom and am installing a bathroom exhaust vent since one doesn't exist. My options are to either go out the asphalt shingle roof (Standard Sloped Roof), or, go out the side of the house through the siding.

The bathroom sits in the middle of the home, so if I go out the roof I can go directly straight up only about 2-3' from the bathroom ceiling and out the roof. If I go out the siding, I'll need to go up, and elbow over about 15' to get to the side of the house.

I'm cautious when it comes to touching the roof, so the idea of going out the side of the house sounds like a better idea with less risk of leaks. However, I know its common to just cut into the existing asphalt shingle roof and go directly out.

I've watched a few videos on how to go out of the roof so I think I have the talents (I'm a extreme DIY type), but I'm still curious what others think on these 2 options.

Out the roof, seal it well and move on? Or consider going the longer stretch out the side of the house. Is one method better than the other for any reason? From experience what is a better method?

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    A comment because I don;t know if you have them where you are - I've got ridge tile vents for my bathroom extractors. The exhaust goes out the roof, but out the very top, so the sealing is simpler
    – Chris H
    Jan 26, 2023 at 13:35

2 Answers 2

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Since you qualify as senior DIY each method can apply.

While going straight up through the roof might be attractive, it does comes with one major problem. Preventing the leak and maintaining the seal over years. The advantage would be the shorter run, and not much restriction in the flow.

The side mount will never leak, but due to the long run it will reduce the exhaust air flow. It could be overcome by using larger size exhaust pipe.

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    You make some great points, thanks for the tip on the larger pipe if I go for the longer run. I need to get up on the roof again but now that I think of it, I'm a little worried that the shingles are slightly older and may become brittle if I start touching them up. They still have plenty of life left in them, but I know its better not to go messing around with them. Depending what I find, if the shingles seem pliable and I can easily get them up I'll probably consider going out the roof. If not, out the side I go! Thanks.
    – RocketManZ
    Jan 26, 2023 at 4:57
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    The fewer holes in a roof...the better. Jan 26, 2023 at 5:54
  • If you go out the side, the warm moist air will rise to you soffits. If you have soffit vents, that warm moist air will be sucked in and promote mold growth inside.
    – Armand
    Jan 26, 2023 at 8:12
  • My personal feeling is the longer/upsized run is worth it for the peace of mind of not having to worry about roof leaks.
    – Huesmann
    Jan 26, 2023 at 12:36
  • @Armand that might be true in the absence of any wind whatsoever. However, pretty much all siding vents exhaust downward (to avoid rain entering the duct), so in order for any exhaust air to get into the soffits, it would need to go down, then up. Additionally, the exhaust air is being blown down and outward, so by the time it makes the turn to go back up, the air stream is further away from the house. I don't think mold is a concern here.
    – Huesmann
    Jan 26, 2023 at 12:39
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My Personal experience says it does not matter, take the one that you are most comfortable doing. I have two internal baths, one in the front so I ran it to the side of the house, one on the back half I put through the roof, both work no problems. I do sometimes get a bit of air moving out of the back when it is windy but not much.

Good luck, I know you will do a good job on the install.

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  • Thanks for the experience on both methods. I'm going to inspect my asphalt shingles and decide from there. The last thing I want to do is break a shingle since its winter season and no time to be trying to redo a roof. Shingle condition will help me determine which direction I go. Thanks again.
    – RocketManZ
    Jan 26, 2023 at 4:58
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    @RocketManZ Shingles do not like winter that much. Will depend if your winter is plus 60 or minus 20.
    – crip659
    Jan 26, 2023 at 12:44
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    Take a heat gun with you, @RocketManZ. Heated shingles will take the bending much better than frigid cold ones will. I'm looking at having to do a plumbing vent up through my roof in the next couple of weeks. I'm hoping for a 40°F day soon...
    – FreeMan
    Jan 26, 2023 at 12:52
  • This raises a good point - it may be feasible to use a Y splitter/joiner to allow multiple rooms to have their own vent to one exit.
    – Criggie
    Jan 26, 2023 at 18:21

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