How to Vent a Bath Fan Through the Roof | This Old House

This Old House general contractor Tom Silva shows how to properly install a roof-mounted bath-fan vent. (See below for a shopping list and tools.)

Tom helped a homeowner with a bathroom fan that was venting moist air into his attic. The fan's vent was installed on the underside of a roof soffit, causing moist air to get sucked up into the attic, which was leading to mold and mildew problems. To correct the situation, Tom moved the vent onto the roof, being careful to flash it properly so there would be no leaks.

Shopping List for How to Vent a Bath Fan Through the Roof:

Tools List for How to Vent a Bath Fan Through the Roof:

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How to Vent a Bath Fan Through the Roof | This Old House

[saschaoswald]

Who else is jealous of the thickness of that roof sheathing and the incredibly easily accessible attic?

[claytonneal]

You know, as a kid I HATED when my dad would watch This Old House on TV. Now as an adult here I am looking up videos of it out of interest or at times need for my own projects.

[dakharding]

Had my entire roof replaced a few years back and I'm dumbfounded to discover when replacing the exhaust fans in my bathrooms that the contractor never bothered to connect the ducts! Now I have to climb up there and do it myself. Lord give me strength fixing other people's laziness throughout the years.

[Real_PK]

I would call it a day after getting those plywood sheets up through the attic hatch to use as a work platform. 6 months later the fan would still be venting thru the soffit and I would be wondering where all my plywood went.

[j_dane]

Always love it when Tom Silva steps me through a project I'm about to take on. After watching this video, I installed a couple vents on my roof. If you're thinking of doing the same, here are a couple notes you might want to consider: (1) My shingles were much less cooperative than the ones in this video (breaking the seal (2:50) without breaking any shingles required a lot of patience). (2) Remember that your initial nail location is a bit arbitrary, so you can make it easier on yourself by adjusting the location so that the top edge of your shingle cut-out is right at the bottom of a shingle course. (3) It looks like Tom only removed the top layer of shingle. Other videos want you to go deeper. I don't know what's right, but be sure to give this point some thought. (4) Tom's vent cap didn't have a duct flange attached to it. This made it easier to slide into place (maybe he got away breaking fewer seals because of this), but it also introduces a condensation risk: moisture-laden air will be flowing (under pressure) through the open area between the flange nailed to the roof and the the vent cap and the plywood sheathing. A simple fix for this is to add sealant between the flange and the plywood. Incidentally, my vent caps had flanges already attached, but the attachments seemed pretty leaky so I sealant where they connected to the vent cap.

[DougCeleste]

Tom and this homeowner have NO fear of climbing ladders at that height. YIKES!!! And credit to the camera person, too, for climbing that high to film this story. Nice work by the guys! 😎

[shanechick]

I watch a lot of home improvement videos and the thing that strikes me the most about TOH and especially Tommy, is the fact that they are so non-judgemental. There are too many content creators that have to denigrate the previous work. Thank you for helping maintain a sense that trying things and fixing mistakes is ok and not out of reach.

[stalex]

mind blown when he did put the nail through the roof. Here I was thinking of measuring distances and all hahah

[tonymusolino]

For me, the hardest part of that job is getting on and off the roof. Love the harnesses, OSHA will be proud. Safety first.
Well done guys. Making it look easier than it is.

[clarkwilliams]

You just saved me from making exactly this mistake: venting my bathrooms right into the soffit vents. Thank you, Tom!!!

[Dcook]

Pro tip. If you can do this on a warmer day it helps a lot. Roof shingles become more brittle to bending the colder they get.

[pelle]

Just followed this exactly to vent both my bathrooms. Was nervous putting holes in the roof but got it done. Came out great.

[joejustus]

Thanks Tom. Up until I watched your video I was going to vent to soffit vent . I never considered the vent sucking the moisture back into the attic. Thanks to you I may have avoided a big mistake.I will be venting through the roof.👍🏻

[stephenbrink]

Tommy is the best. Years ago I was wearing my "This Old House" hat and Tommy was at the fair at a booth. We talked a while and he signed my hat and a picture. This video inspired me to install a vent into my upstairs bathroom in my 1880s house. Thanks Tommy!

[terryallard]

Tom Silva is the best. I have always enjoyed watching him over the years. A great talent as a craftsman and teacher.

[Pataclese]

Tom Silva does such a great job walking everyone through intimidating jobs. Thank you.

[Them]

I want the whole This Old House crew to build my house. I love these guys. You know they can be trusted and that's something money can not buy...a piece of mind.

[samuelhalajian]

I’m a new homeowner and just discovered this series - I can’t express how grateful I am for it. I am learning so much about the anatomy of my home, and the teaching style here is clear, concise, and instills confidence in my ability to tackle projects I’ve never done before. I don’t know if Tom actually monitors these comments, but THANK YOU SO MUCH!!

[daakrolb]

Beautiful work by one of America’s true men Mr. Silva!

[Arpin_Lusene]

Very informative, straight to the point, and very practical! Great video.