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When I purchased my house, during the home inspection it was indicated that the bathroom vent is simply discharging directly into the attic space. Because we were concerned about mold in the attic, we've simply not used the fan. The inspector indicated that we'd need a vent pipe that went straight up through the roof.

My attempts to hire someone to do this work continue to fall flat, but in speaking with a contractor the other day, he'd indicated that the vent could instead go through the roof soffit instead of through the roof itself. Is this accurate? I wasn't sure if this would create condensation issues either in the vent line or along the side of the house where it vents out.

I saw several other questions relating to this which all seem to indicate this is a bad idea, but they're several years old and I'm not sure if there have been any changes in technology that would make this more viable (maybe modifications to the soffits around the discharge point to prevent the humid air from being pulled back in and preferred pipe slopes to prevent condensation buildup).

If it's relevant, we're located in South Jersey, which sees a lot of temperature fluctuations throughout the year (and often throughout the day).

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  • Jersey is also very humid in the summer. Normally, a wall mounted vent cover would have gravity activated flaps that have near zero resistance to the air blowing them open, then gravity pulls them closed when the fan's off. I believe the main issue with a soffit vent is that you need a spring-loaded vent cover to keep things (bugs) out of vent when it's not running and a strong enough fan to push the vent flaps open when it is running. You might get away with covering the soffit vent opening with simple hardware cloth/window screen to keep the critters out (con't...) – FreeMan Feb 26 at 16:37
  • but that leaves you with an unblocked opening for cold air to blow into the house in the winter. It's not like a standard gravity flap is insulated, but it does a reasonable job of preventing cold air from blowing directly in. – FreeMan Feb 26 at 16:38
  • I think the main issue with a soffit exhaust is that the warm, moist air coming out can be drawn back into the attic through the soffit vents. – SteveSh Feb 26 at 17:25
  • And I vented a exhaust from a powder room out the roof with no problems. There's a post here somewhere with pictures that show that installation. diy.stackexchange.com/questions/178107/… – SteveSh Feb 26 at 17:27
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I am not a roofer, (although I have worked on roofs before) but recently did replaced my bathroom fan and from the information I gathered (much like you) the issue is that the air is rising, hot and full of moisture which will go back into the soffit. How much of a problem that is, it's hard to know since this commonly done that way (because of how much simpler it is probably). The other issue here (currently) is that you'll be trapping moisture in your bathroom, so you'll be getting mold there unless its vented well, doors / windows open that kind of thing, so I'd get this done soon.

As I said, I've recently replaced my bathroom fan. In my case, it was the wrong size fan, with a smaller pipe then what was needed, venting out of the soffit. Although it was probably working for about 15 years, there was no "visible damage". However, I would never do it that way, for the reasons mentioned. So I cut a hole in the roof an vented it there. It's fairly simple and there are plenty of videos on youtube on how to do this. Given that yours is venting to attic already, means that you probably have very easy access to the pipe and underside of the roof. This should make this even more of a simpler process. You can mark the underside of the roof and drill a starter hole. No need to "blindly" find rafters. Or, a roofer should be able to do this for you easily.

All things considered, between leaving the fan off, venting it to the attic or through the soffit, venting it through the soffit is certainly the best choice by far.

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  • Sounds like I might be asking a question about roof flashing soon. – Pyrotechnical Feb 26 at 18:39
  • @Pyrotechnical shingles? – sheetmetal85 Feb 26 at 18:41
  • I had looked at a video on doing the vent myself and it was discussing the proper way to to metal flashing around the pipe itself coupled with the shingles to prevent water intrusion at the penetration. – Pyrotechnical Feb 26 at 20:51
  • I used one of those standard rectangular roof vents over the pipe terminations, sealed everything and placed water directionally under the shingles. – sheetmetal85 Mar 1 at 12:29
  • I'm having difficulty envisioning this. Can you provide a picture? – Pyrotechnical Mar 1 at 16:12

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