Not exactly a garage topic - plumbing vent pipe

[dantheman8119]

Hi everyone,

I have a 2" pvc plumbing vent pipe exiting out of my roof that is freezing over every few days now that we are in full on winter in Minnesota.

Does anyone have any ideas for how to prevent this from happening? I'd like to avoid using heat tape if at all possible

One idea i've read is to hang a long piece of copper pipe with a T soldered on the end of it, as that helps to conduct the heat in the pipe better? I would then basically hang that at the top of the pipe on the T

 

[Jackfre]

Extending the vent might help, but I think increasing the size to 3" in the attic and up above the current level would be best.

 

[dantheman8119]

I'd agree...although I need to take a close look to see if I would have access to it from the attic, as we have an A-frame style house.

 

[BigGMC]

I had thought all vents through the roof , in cold climates, had to be 3" just for this reason.
My home is 2" up to the attic, then it expands to 3", I always thought it was odd and assumed it was some sort of contractor short cut. Later found out it was pretty common place - just the protion exposed to cold was increased to 3".
Not sure i understand how the copper pipe trick would work...... still going to have warm moist air coming up through the pipe and condensing/freezing when it hits the unheated attic or exterior. Not expensive, give it try.

 

[1SlowFormula]

I will caveat this with, I have never lived in an area that freezes like your area.

Where is the "Thermal Break" in your house? Is it at the roofline or floor of the attic space. How much of the pipe is in the freeezing temperatures, e.g. 6' of freezing attic then 18" above the roofline?

This MAY be a case where you just have too much length in the freezing temps and in that case I would suggest removing the insulation, boxing in the pipe and extending hot conditioned air up into that pipe chase. To do that I would remove the insulation around the pipe in the attic, frame a box around the pipe, insulate the roofline (vented if possible) on the inside of your box, sheet the boxe then insulate the exterior of the box. That would, simply put, make a small, unheated, but not freezing room around the vent line in the attic.

This all being said if you have the thermal break in the roofline and a non-freezing attic, ignore my post, lol...

 

[readhead]

What do you mean by "freezing over"? Is the snow above the top of the pipe? If that is the case just take a longer piece of 3" and place it over the 2". However this could make a new problem and you might have to place a diverter on the roof above the pipe to keep it from being broken off.

 

[kbs2244]

If your problem is the moisture being vented is freezing, then to get you through this winter I would go with some heat tape.
Then, come summer, make the vent meet code and increase the through, and above, roof to at least 3 maybe 4 inch pipe.
The idea is that the moisture in the larger pipe will still freeze around the outside but the larger dia will mean there is still a hole through the center.
Your code should call out both a dia size and a length above and below the roof for that size.

 

[Stuart in MN]

It appears that the vent stack needs to be at least 3" in diameter to meet code in Minnesota: https://www.revisor.mn.gov/rules/?id=4715.2330

 

[The Cobbler]

In school, the plumbing teacher called this hoarfrost. increase the vent to 3" before the roof line .

 

[Gary S]

Up here, we use larger pipe, around 3-4", and we run multiple pipes out of the roof on different sides of the roof so the wind can't hit all of them directly. Having multiple pipes through the roof and having them all connected horizontally in the attic seems to solve the problem of them icing over.