Bathroom Venting

[brnhornt]

Hi gang...quick question...I need to add/install a bathroom exhaust fan in my second bathroom.  I know that you should never vent warm bathroom air into the attic space (especially in cold climates like here in Cleveland) so I've been planning on hiring a contractor to come out and install the vent/flashing for me....but a thought just popped in my head.  In addition to the ridge and soffit vents...there is a 2'x4' gable vent for makeup air.  Is it ok to attach the flexible, insulated exhaust duct to that?  Saves me a bit of money...but also the additional hole in my siding or roof.

Thanks!
Kevin

[Robert Adams]

With ridge and soffit vents the gable vents should be blocked off anyway. I don't see a real issues with using that gable vent but it needs to be blocked off to other airflow to keep the moist air from going back in the attic.

       Not ideal but I don't see why it wouldn't work ok.

[Snipe Hunter]

Like Mr. Adams said. Block the gable vents if you have ridge and soffit vents or you will have the corners of your attic without moving air. It's where I usually find mold in attics... assuming the soffit vents are actually venting and not plugged with insulation.

Something I've seen in quite a few homes is the bathroom vent duct terminating about 2-3" right under the ridge vent. I've never seen one done that way with any discoloration on on the wood or mold and it gets cold here. I know for a fact that it doesn't meet code here. I believe that it's acceptable in some areas. I make note ("not accepted construction standards") of it in home inspection reports but I also tell the client that it is in fact venting to the outside and I know that because there is no evidence of current or previous moisture in the area. I don't give my opinions or quote code (not legal here) in reports I just observe and report. It's a cheap easy way that is effective.

There are also soffit vents made just for this that do meet code. The problem with them is that you can't easily get 3" rigid metal duct to that area (pretty sure bathroom fans are 3" duct) . It can be done but it's not easy. You also can't have too many elbows. If you decide to use a soffit vent with flex duct, use the metallic flex duct, not the plastic. The metallic has a lot smoother surface  and moves air better than the plastic.

3" soffit vent/ Lowes

Here's some good info for venting.

[JosephP]

I'd recommend insulated vent pipe to cut down on the condensation building up in the pipe on cold days.

[brnhornt]

Valid points.  Never thought about the gable vents needing to be blocked.  The home was built in 1988...anyone know if ridge vents were common practice?  I have this rectangular gable vent on the West side of the attic...and then a 12-24" diameter round one on the front/South side.  The way this area of the attic is set up I don't have direct access to the soffit vents, but I can see them from the outside as well as there is cardboard spacers/channels in the attic joist bays and then the insulation is pressed up against that...so I hope they are actually working.  This is a rather large bathroom space that I am going to be venting (standard square footage, but huge ceilings) so I'm going with a FanTech....they use 4" ducts and I will definitely be using insulated ducting.

I'm wondering if the ridge vent was cut in when the roof was replaced.  If so, then I don't have any problem blocking off the rest of the existing gable vent minus a 4" hole for the vent...but I'd be a little worried if the original builder/architect planned for it from the beginning and here I am messing with that.

Curious...with those venting 2-3 inches below the ridge vent...isn't there usually some kind of mesh to keep the animals out?  I would think in the winter that would catch moisture and end up freezing and causing issues later....

[Robert Adams]

Valid points.  Never thought about the gable vents needing to be blocked.  The home was built in 1988...anyone know if ridge vents were common practice?  I have this rectangular gable vent on the West side of the attic...and then a 12-24" diameter round one on the front/South side.  The way this area of the attic is set up I don't have direct access to the soffit vents, but I can see them from the outside as well as there is cardboard spacers/channels in the attic joist bays and then the insulation is pressed up against that...so I hope they are actually working.  This is a rather large bathroom space that I am going to be venting (standard square footage, but huge ceilings) so I'm going with a FanTech....they use 4" ducts and I will definitely be using insulated ducting.

I'm wondering if the ridge vent was cut in when the roof was replaced.  If so, then I don't have any problem blocking off the rest of the existing gable vent minus a 4" hole for the vent...but I'd be a little worried if the original builder/architect planned for it from the beginning and here I am messing with that.

Curious...with those venting 2-3 inches below the ridge vent...isn't there usually some kind of mesh to keep the animals out?  I would think in the winter that would catch moisture and end up freezing and causing issues later....

          Ridge vent is still a fairly new thing. Started gaining ground in the 90s. Yours would have been done when the roof was replaced.
        I like ridge vent but it had one major drawback no one mentions. It massively reduces the strength of the roof. You cut out the sheathing at the peak or you hold short of the peak when installing new sheathing. Now there is no sheathing attached to the rafters and the ridge beam. A huge loss of integrity lost there. 

       Running exhaust to soffits is and royal pita unless you have a 12/12 roof. It's very tight there and getting even a 3" aluminum flex duct is a tight fit.
 
         There are vent caps that have a big plastic mesh to keep the birds out etc. As for water freezing on them. It's a possibility like it is for exhausts for high efficiency furnaces and water heaters. But my thoughts are not to worry about it unless you were somewhere like northern Minnesota or Canada.

[CLETUS]

        Now there is no sheathing attached to the rafters and the ridge beam. A huge loss of integrity lost there. 

       

Not true.

[Robert Adams]

Not true.

Uh yeah very true. There is no sheathing overlapping the rafters and the ridge beam. So the only thing holding the rafters to the ridge is a couple nails. With full sheathing it is all fastened to eachother.

      Take a look at any of these pictures and you will see nothing attached to the ridge beam anymore other than the rafters. 


        https://www.google.com/search?q=cutting+...0&bih=1594

[CLETUS]

Uh yeah very true. There is no sheathing overlapping the rafters and the ridge beam. So the only thing holding the rafters to the ridge is a couple nails. With full sheathing it is all fastened to eachother.

      Take a look at any of these pictures and you will see nothing attached to the ridge beam anymore other than the rafters. 


        https://www.google.com/search?q=cutting+...0&bih=1594

One nail in each side of the ridge beam isn't overcoming the " huge loss of integrity"

[brnhornt]

Thanks Robert...sounds like it's worth blocking off this gable vent and venting the insulated duct directly thru it.