Roof vent pipe premature snow melting issue - how to fix?

[Don2222]

Hello


This is a very tenacious problem since I have tried many things. These houses was built in 1962 and the outside walls have approx 2" of fiberglass insulation. The stink pipe is for the toilet, tub, washer and sink.
The pipe exits the roof above the right side of the bathroom window as shown in the pics below.
Most of the houses in my neighborhood have this heat loss issue! ! !


It seems that when the snow melts, why does the snow on the roof melt here? See pics
The original stack was made of copper and only extended 6 inches off the roof. I tried extending it with pvc last year but that did not help very much
See pics https://www.hearth.com/talk/threads...on-the-roof-before-winter.89970/#post-1173890

So this time I tore out the whole copper stack and replaced it with PVC so no heat would not be conducted up thru! Then I opened up the bathroom wall and tore out the 2" fiberglass and replaced with ROXUL ! Then I put in a new double pane double hung window and sealed all around it with foam sealant. The worst heat loss and air leak in the old windows was not the window but the frame around the window with no insulation between! ! !
Before I closed up the wall I air sealed the gap where the ceiling sheet rock meets the top plate (2x4) in the exterior framing! Above the bathroom ceiling is 2x6 R19 Fiberglass insulation crisscrossed with R30. The roof rafters have rafter vents from the continuous strip vent in the middle of soffit all the way up to the ridge vent. with r3.8 reflectix foil stapled to the bottom side.

See 2nd pic below. It is much better but why is it melting faster at this point now? Where is the heat loss? Sorry for the fuzzy pic

 

[Highbeam]

I bet your pipe is blocking the ventilation air that would normally enter in the soffit, travel up the underside of the roofing unimpeded, and then out the top. That big plumbing vent is slowing the flow of air relative to the others and slow air isn't able to wisk away your leaked heat from the house so it melts the snow there.

That tiny dusting of snow could melt if a mouse farted under it.

It's an idea.

 

[heat seeker]

Maybe heat gain - from the sun, reflecting off the pipe? Yeah, a long shot…I like Highbeam's idea.

 

[Highbeam]

In the fuuzzy picture, you can almost see a reduction in meltoff at the ridge in that same rafter bay which would jive with a lack of flow.

 

[Utilitrack]

No such thing as a "premature snow melting issue" after this winter!

 

[Don2222]

Good ideas

I just found a pic of the issue before the new window, before the Roxul insulation in the outer wall and before I put the PVC in and air sealed it.

It looks like the problem has moved to the right!

The only thing that would make sense, is the fact that I air sealed where the ceiling sheet rock meets the top plate above and slightly to the right and levt of the window. I did not air seal the section to the right where the problem shifted!

See pic. Click to Enlarge.

 

[Highbeam]

I don't see how it moved much if at all. Your rafter spacing is 16 or 24, probably 24".

 

[woodgeek]

I'd vote for an airsealing issue near the top plate. Is there something in the wall cavity under that could be feeding the leak. That is, the gap in the plate might be uniform along the wall, but there might be something in that wall cavity allowing air in??

 

[Warm_in_NH]

I think Highbeam hit the nail on the head with the obstructed air flow. It's not uncommon. If you're not getting leaking ice dams I wouldn't worry too much about it.

 

[Don2222]

I'd vote for an airsealing issue near the top plate. Is there something in the wall cavity under that could be feeding the leak. That is, the gap in the plate might be uniform along the wall, but there might be something in that wall cavity allowing air in??

Yes, Woodgeek, I think you are right on track here. The proof of this happened when I took the wall board off on the outside wall in the bathroom. The warm air in the bathroom super fed the air leak between the ceiling sheetrock and top plate and made the melt mark 10 times greater!

Now in this last case, I think that because there is only approx of 2 inches of insulation in the 2x4 outer wall, that there is warm air in the cavity on the inside of the insulation. This slightly warm air is being drawn up by the vacuum created when the soffit air runs up to the ridge vent. Why it only occurs near the bathroom is another question, but because of the hot showers, the bathroom is much warmer and humid too!

I was amazed when I saw that gap between the ceiling sheet rock and the top plate! ! !
This would also explain why the melt area is close to the edge of the roof where that gap is! ! !
When I get up there and seal it I will take pics. Did you seal that area in your house Woodgeek?

 

[Highbeam]

Yes, Woodgeek, I think you are right on track here. The proof of this happened when I took the wall board off on the outside wall in the bathroom. The warm air in the bathroom super fed the air leak between the ceiling sheetrock and top plate and made the melt mark 10 times greater!

Now in this last case, I think that because there is only approx of 2 inches of insulation in the 2x4 outer wall, that there is warm air in the cavity on the inside of the insulation. This slightly warm air is being drawn up by the vacuum created when the soffit air runs up to the ridge vent. Why it only occurs near the bathroom is another question, but because of the hot showers, the bathroom is much warmer and humid too!

I was amazed when I saw that gap between the ceiling sheet rock and the top plate! ! !
This would also explain why the melt area is close to the edge of the roof where that gap is! ! !
When I get up there and seal it I will take pics. Did you seal that area in your house Woodgeek?

I'm interested in the pics Dan because I too have a 1963 built house with that weird 1.5" thick R-5 batt insulation in the 2x4 walls.

 

[Don2222]

I'm interested in the pics Don because I too have a 1963 built house with that weird 1.5" thick R-5 batt insulation in the 2x4 walls.

Hello HighBeam

Here is a pic where we shot the Expanding Foam from below when the sheet rock was off! The gap got larger, because the sheetrock was not straight against the top plate!

Anyway, it should be easier and better to just put the foam in from the attic. I put plywood sheets across the rafters so I do not fall in, then just scrunch down there close to the gap and do the foam thing.

 

[woodgeek]

I was amazed when I saw that gap between the ceiling sheet rock and the top plate! ! !
This would also explain why the melt area is close to the edge of the roof where that gap is! ! !
When I get up there and seal it I will take pics. Did you seal that area in your house Woodgeek?

I got all the interior and gable end top plates with Silicone caulk for 'attics'. With my low-slope roof I couldn't reach the exterior walls on the eaves. I had pros hit that area with sprayfoam. Not clear how effective that 'spray and pray' method is, but even with a huge snow load (for us) last winter, I did not get many icicles, and no ice dam problems.

 

[Don2222]

I got all the interior top plates with Silicone caulk for 'attics'. With my low-slope roof I couldn't reach the exterior walls on the eaves. I had pros hit that area with sprayfoam. Not clear how effective that 'spray and pray' method is, but even on a huge snow load, I did not get many icicles this winter, and no snow dam problems.

Very good, That spray foam probably got it. I have a 30 Deg slope so I can get in there. I will get that area soon.

 

[BrotherBart]

I have a 30 Deg F slope so I can get in there.

It would be harder if the slope was Celsius.

 

[Don2222]

It would be harder if the slope was Celsius.

Yes, I was thinking to much about heat lately! ! ! LOL

 

[Don2222]

Hello

Here is the lates update and the most penetrating invasion for a more comprehensive fix!

Last spring I had the coopper vent stack changed to PVC from the basement up thru the attic and made it extend one foot off the roof.

I also opened up the wall in the bathroom and ripped out the the old R7 Fiberglass insulation and replaced it with ROXUL for 2x4 studs which is R15 and air sealed the gap between the top plate and ceiling sheet rock! ! !
That change did improve it alot more

Do you think I should add anymore insulation under the rafters for good measure?

See pics

Pic 1 - New PVC vent pipe
Pic 2 - 4 - Neighbors vent pipe for comparison

Click pics to enlarge

 

[Hogwildz]

Your going to get heat transfer from the pipe even if it is PVC. Not as bad as the copper, but you have warmer air traveling through the pipe, which will transfer to the pipe and to the flashing.
No amount of insulation under the rafters is going to stop the heat transfer happening between the rafters and up top of the roof where the pipe is exposed.
If anything, I would try wrapping the pipe in the area under the roof deck and see if that helps. Looks like you are doing much better than your neighbors.
A 3" or 4" vent pipe is not going to block enough air flow from the soffit vents to the ridge vents to cause any issues with ventilation, whether the rafters are on 16" or 24" centers.
Make sure you didn't accidentally block air flow at the top plate between the rafters.
R15 for walls is not the greatest, but you can only fit so much in a wall, and is surely better than R7.
I think you're looking good, and any more expense & labor would not be cost or time effective, aside from maybe wrapping the pipe in the attic space.

 

[gzecc]

As long as the living envelope is adaquately insulated, you should be opening vents in the soffit to cool you attic space. There will always be melting, but if that melting is premature than you need more cold air in your attic/rafter bays to keep your roof cold.

 

[Don2222]

Your going to get heat transfer from the pipe even if it is PVC. Not as bad as the copper, but you have warmer air traveling through the pipe, which will transfer to the pipe and to the flashing.
No amount of insulation under the rafters is going to stop the heat transfer happening between the rafters and up top of the roof where the pipe is exposed.
If anything, I would try wrapping the pipe in the area under the roof deck and see if that helps. Looks like you are doing much better than your neighbors.
A 3" or 4" vent pipe is not going to block enough air flow from the soffit vents to the ridge vents to cause any issues with ventilation, whether the rafters are on 16" or 24" centers.
Make sure you didn't accidentally block air flow at the top plate between the rafters.
R15 for walls is not the greatest, but you can only fit so much in a wall, and is surely better than R7.
I think you're looking good, and any more expense & labor would not be cost or time effective, aside from maybe wrapping the pipe in the attic space.

Thanks, I like the idea of wrapping the pipe. That would be quick and easy and stop any heat transfer to the pipe! Thanks alot!

 

[Don2222]

As long as the living envelope is adaquately insulated, you should be opening vents in the soffit to cool you attic space. There will always be melting, but if that melting is premature than you need more cold air in your attic/rafter bays to keep your roof cold.

Agree, I have rafter vents from the soffits all the way to rhe ridge vent. Under the rafter vents I have R4 relectix foil. That gives plent of cool air under the roof! No ice dams afetr doing that!


Here is my story.

I have a split Entry home built in 1962

A. Save heat in winter by insulating Attic Floor better and closing up gable vents

Pic 1. Rip 2x4s down to create 2x2s and nail them to the 2x4s.
Remove OLD R7 Stamped ECONOMY Owen Cornings Fiberglass Paper Faced Insulations

Pic 1. Air seal all holes with Can Foam
Roll down Reflectix Foil R3.9 then roll down R19 Fiberglass Paper Faced Insulation on top of Foil

Pic 2. Criss Cross with Unfaced R30 Fiberglass insulation for a tolal of R53 in floor!

Pic 3. Since I now have a Ridge Vent and Soffit Strip vent I built doors to close gable vents in Winter
Also insulate and foil Gable Vent End Walls for better insulation. amazing now by doing tha the paint never peels in the outside triangle where gable vent is because there is no extreeme temp diff between inside and outside!!
Saves a tremendous amount of heat being sucked out of the house from cold winter winds blowing in!!

B. Save Air Conditioning cost in summer by reflecting heat and keeping cool in!

Pic 4. Staple Rafter vents from soffit all the way up to ridge vent to maintain cool roof!

Pic 5. Staple Reflectix foil over rafter vents to keep whole house 10 Degrees cooler in summer
Only need air conditioning if too humind now, never gets too hot!!

Open Gable vent doors for additional cooling!!

End result Big $avings in summer and winter!!

 

[ironpony]

simple answer. the other end of he pipe is connected to the sewer or septic tank. the air temp in those areas underground are probably around 50 degrees. the stack is acting like chimney and drafting warm air constantly thru the pipe causing melting, it is a vent pipe after all.

 

[semipro]

Don,
Do you have a ventilation fan in that bathroom? I don't see a vent for one.
I was wondering if perhaps you have one and its vented to the soffitt area?

I like Woodgeek's thoughts on a leak at the top plate. I'd assume there's a penetration in the plate where the vent pipe comes through but I would think you've already sealed that. The trouble is hot spot doesn't align with the penetration, that is, unless there is a jog in the vent pipe that takes it out the roof at a higher point than where it comes through the top plate.

Hog may be on to something also but its hard to understand why snow melting at the stack would show up closer to the eaves after flowing under snow below the vent?

 

[Bret Chase]

simple answer. the other end of he pipe is connected to the sewer or septic tank. the air temp in those areas underground are probably around 50 degrees. the stack is acting like chimney and drafting warm air constantly thru the pipe causing melting, it is a vent pipe after all.

Yup... and the wind flowing up and over the roof will cause eddying which will move snow, esp when mixed with the warm air coming out of the vent stack. Basically the OP has got it about as good as it is going to get.

It's alot like the leeward side of my roof... it rarely has icicles, or snow, not because of insulation or air sealing (my house's ACH is between LOL and OMFG), it's simply because the near constant west wind just blows it off.... and piles it in my driveway.

 

[Don2222]

Don,
Do you have a ventilation fan in that bathroom? I don't see a vent for one.
I was wondering if perhaps you have one and its vented to the soffitt area?

I like Woodgeek's thoughts on a leak at the top plate. I'd assume there's a penetration in the plate where the vent pipe comes through but I would think you've already sealed that. The trouble is hot spot doesn't align with the penetration, that is, unless there is a jog in the vent pipe that takes it out the roof at a higher point than where it comes through the top plate.

Hog may be on to something also but its hard to understand why snow melting at the stack would show up closer to the eaves after flowing under snow below the vent?

Thanks, yes I do have a vent fan and it vents properly to the left end of the house.

I think that big gap between the sheet rock and the top 2x4 of the wall framing was the real culprit! when I opened up the wall, I could see into the attic so there was just a little