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Author:
Anonymous User
What would be the recommended height of the vent above a very low pitch roof ( 1.2/12 )?
This is in Minnesota, and the sole exsiting 2" vent, which is extends about 14" above the roof, froze shut with condenced vapor several times last winter in very cold weather. Would I be better off cutting it off shorter?
I am installing a new bath with a 3" vent going out the roof and am wondering if the 10" minimum height would be better, or to make it a longer due to the snow depth we accumulate on the roof.
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Author:
e-plumber (NY)
"What would be the recommended height of the vent above a very low pitch roof ( 1.2/12 )?
This is in Minnesota, and the sole exsiting 2" vent, which is extends about 14" above the roof, froze shut with condenced vapor several times last winter in very cold weather. Would I be better off cutting it off shorter?
I am installing a new bath with a 3" vent going out the roof and am wondering if the 10" minimum height would be better, or to make it a longer due to the snow depth we accumulate on the roof."
>If the 2" stack vent is going to remain in addition to the new 3" vent, I would cut it 12" below the roof line, (in the attic if you have one) and increase it in size to 3" or larger, then penetrate the roof line and terminate the pipe 12" above.
This would be code here, MN may be different.
e-plumber
e-plumber
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Author:
dubldare (MN)
MN 4715.2530 subpart 1: Extension above roofs. Extension of vent pipes through a roof shall be terminated not less than 12 inches above it. Where a roof is to be used for any purpose other than weather protection, the vent extensions shall be run at least seven feet above the roof.
I'd maybe try to tie that existing 2" vent into your new 3". If that's not possible, install a Moore flange or a Mpls code roof flange. They're the type with the telescoping sleeve that attatches to the pipe. It will help to insulate the vent and keep that hoarfrost from happening.
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Author:
hj (AZ)
Chicago required a minimum 4" pipe through the roof 12" high. If the vent was 4" or larger, then the pipe through the roof had to be increased one size. If it is too high then the heat from the building will be dissipated and the condensation will be able to freeze in the extended portion and close off the vent.
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Author:
Anonymous User
This roof is built directly on the ceiling joists (2X10's) so I have only that 10" to work in.
The 2" had the telescoping type flashing on it when I bought the house and that was the setup that was freezing over. That was always the accepted 'best choice' for this climate but did'nt work for me.It would be impossible to tie the two vents togeather with the roof construction being what it is.
I have now cut off the 2" within the roof joist cavity and added a piece of 3" extending above the roof about 14" and then flashed it with a steel/neoprene flashing boot. I have also insullated the joist space in the whole roof(there was 1" before)so perhaps that will help also. At least it will now be a larger opening to freeze over.
I think MN code requires a minimum 3" vent, hj ,which is why I added the new one from my new bathroom.
So far I think your saying cut it off at the code minimum, right?
Trying to understand, LOL
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Author:
dubldare (MN)
MN code requires at least one 3" vent stack carried full size through the roof. This does not mean a few smaller vents (1 1/2 & 2) connecting and then increasing to 3" through the roof, it means at least one soil or waste stack extending through the roof with a minimum diameter of 3". The main reason is to ensure proper ventilation. Also, in multistack situations, the most remote stack must be fullsize through the roof.
As far as minimum size, 2" is the smallest vtr. This is to try to prevent freezing. ;{
Increasing to 3" is probably your best alternative to prevent the hoarfrost. As long as you're increasing on the vertical you'll have no problem.
Although, your bathroom addition and its vent will also help ventilate the sewer; which hopefully help with the freezing problem too.
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Author:
Anonymous User
Thanks dobldare, The new bath vent is 3" and is the farthest away so I think i"m on the right track.
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Author:
Anonymous User
I can rember installing the 2"*4" as well as the 4"*5" increasers on the main stack, sure seems weird now.
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Author:
Anonymous User
Also, if it is white PVC spray paint the pipe black that comes through the roof, it helps cut down on the frost.
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Author:
hj (AZ)
Weird? Why? It was logical 30 years ago, and still is for cold weather areas.
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