90 degree elbow for Bathroom exhaust duct

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Old 03-23-20, 03:57 PM
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90 degree elbow for Bathroom exhaust duct

After discovering the bathroom exhaust fan duct vents to the attic, I want to extend out through the roof. It is only about a foot in from where the rafters meet the floor joist, (hope my terminology is correct) and about half that to hit the roof. I put a 90 degree elbow on with the intent to just go straight up and out but, after doing some research I'm finding that a 90 degree that close to the exit opening of the unit will cause problems. Going more towards the back joist will make it too tight of a space to work with and it can't go straight back and out because there in an addition to the house on the other side. Actually, that area is about where the roof from the addition overlaps the original roof, so the duct will most likely be going through 2 roofs. Regardless, I believe my bigger issue is how to duct it if I can't use the 90 degree? Picture is attached.
 
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Old 03-24-20, 05:01 AM
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If I had a choice I would attempt to duct through the the blocker at the rafter tails and vent through the sofit than go through the roof just so I wouldn't have to introduce a new possible leak path.

That being said, why do you think going straight up with a proper roof vent be an issue?
 
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Old 03-24-20, 05:45 AM
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90's aren't great because they hurt airflow a lot more than straight duct but there isn't truly anything "bad" about them. So, you can go straight up and out the roof if you want. I'm with Marq1 though, I would much prefer to go out the soffit if I can. It's a location protected from the weather so it's almost impossible to have a water leak or get buried under snow. Access in your case looks difficult so I'd look and measure carefully to make sure you can do it before attempting the soffit. If you go through the roof take a piece of string with a weight on the end up in the attic with you. Hold the string on the roof and center the weight over your duct. Then mark where you're holding the string and that's the center for you to drill.
 
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Old 03-24-20, 06:08 AM
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If you go through the soffit then check that it is not over an area where you walk as you will likely get dripping and icicles,

It is hard to tell how he fan is installed but I would be tempted to turn it 180 degrees,
Then use a 45, a length or straight pipe then another 45.
This will put the vent higher up on your roof.
 
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Old 03-24-20, 06:55 AM
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Marq1 Ė To go straight up, Iíd have to use the 90 degree elbow. According to research Iíve done, a 90 degree will interfere with airflow or what Pilot Dane said.

As for other responses suggesting going thru soffit, there is no soffit there. There is an addition to the house on the other side of what should be a soffit. Its roof line starts about where that duct is and extends out about another 15ft. Also, I believe itís against code in my area to vent out a soffit.

Pilot Dane Ė Good tip on the string, will use that if I go that route. Which is pretty likely, doesnít seem to be a better option. However, I was also concerned about the snow/leak thing too. Only had the roof done 2 months ago. Just couldnít get this project figured out in time.

manden Ė I actually tried turning it around for the same reason, to be higher on the roof, but the configuration of the unit didnít line up. It mounts to the joist on only one side. Mounting it to the opposite joist would require making another hole in the bathroom ceiling/patching.
 
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Old 03-24-20, 08:53 AM
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A new roof actually makes your job easier. If needed you can pull shingle tabs up without them cracking or breaking.
 
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Old 03-24-20, 09:03 AM
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So 90's increase resistance for air flow so they are not bad, they can just be an issue if long runs and too many are used. With that short distance you have no issue.

So one last question, whats in the opposite direction?

Also, I believe itís against code in my area to vent out a soffit.
So for clarification, you would not be venting into the soffit, you would have a vent that attaches under the soffit ant your duct attaches to that, essentially ducting to the outside! Goggle soffit vents!

 
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Old 03-24-20, 09:35 AM
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You could build a box out of 2X6 or whatever then attach that to the right joist then attach the fan to that.

If you go this route then use screws you do not want to be up there banging away with a hammer.
 
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Old 03-24-20, 09:48 AM
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Instead of using a 90...... you could use two 45's for less restriction.
 
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Old 03-24-20, 10:27 AM
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Marq1 - Not much in opposite direction which is why did I try to turn the unit around. But due to the way it mounts on only one side, and the offset of the output ended up right under that rafter to the left, it didn't seem to work.

But now, considering "mandens" idea:
"You could build a box out of 2X6 or whatever then attach that to the right joist then attach the fan to that."
and combine it with his idea of:
"I would be tempted to turn it 180 degrees, Then use a 45, a length or straight pipe then another 45. This will put the vent higher up on your roof."
May be worth a try. Will be tilted to the left a bit going up to avoid the rafter but I'll try it out.
Will post back any results. Thanks all!
 
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Old 03-25-20, 06:00 AM
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Mandens correct. It should be a simple matter to to remove the fan and turn the unit 180*. It's either screwed or nailed to the rafter/truss. You shouldn't need to build a box. The existing 90 is fine to use, go straight up through the roof, and use a good cap. You may have to disassemble part of the light, if it's a combination light and fan, but that's a simple matter. It's possible to run drywall screws right through the side of the box and into the existing rafter.
 
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