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Water drips from drain stack and furnace vent in basement during hard rain

Water drips from drain stack and furnace vent in basement during hard rain

Old 11-12-02, 07:55 AM
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Water drips from drain stack and furnace vent in basement during hard rain

I have the problem listed in the subject - I assume that I have a leak where my drain stack and my furnace stack go out through the roof. My house is 8 years old and I have never sealed/resealed these pipes on the roof.

This is the first time my drain stack has leaked. The drain stack is connected vertically to one of my sink drains - there is an elbow below the first floor in the basement. The water dripped off the elbow during the storms earlier this week - it was dry a few hours after the rain stopped. There was no other evidence of leakage (wet drywall, ceilings, etc) so I am assuming that the water leaked by the rubber seal where the stack emerges from the roof and ran down vertically to the basement... Does this sound right and if so what is the best way to fix it (caulk, roof pitch, etc)?

As for the furnace stack, it is 6" galvanized - it drips in the basement every time it rains hard but there has never been any evidence of water anywhere else (walls, ceilings, attic, etc). It looks like it has metal flashing where it emerges from the roof and then a ~4' section extending above the roof, topped by a vent cap (looks like a couple of mushrooms on top of each other). It looks like the joint between the 4' riser and the pipe that comes through the roof has some cracked roof pitch on it. Could this water be getting inside and leaking out in the basement (since the ducting is put together similarly to HVAC ducting) or is it getting in through the cracked pitch or possibly by the flashing? Should I try to seal it with pitch or caulk (I assume this pipe is hot to the touch where it emerges from the roof)? Any suggestions would be appreciated.

Old 11-13-02, 08:00 AM
Mike Swearingen's Avatar
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Use black plastic roofing cement around the rubber boot of the drain/waste/vent stack.
It is VERY sticky, and will even seal in the rain, so use old clothes, throw-away rubber gloves, etc. I use a paint stir paddle to apply it.
You will need some type of furnace or fireplace (heat resistant) cement to repair the furnace stack. Ask at the store.
Good luck!
Old 11-26-02, 09:37 AM
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Thanks for the reply.
I finally got up on the roof to check things out last weekend and found that both santiary vent collars were cracked and split where they seal the pipe. I used roof pitch to seal them.
My house is only 8 years old but I would guess that I would need to replace this thing in the next couple of years.
Is it normal for these rubber seals to degrade like this?

As for the furnace stack - it is a 'B' vent (if I remember correctly) so the outer shell does not get very hot. I had a tube of furnace caulk but went ahead and used roof pitch to seal around the storm collar. The old sealer had all cracked and the joint below was not sealed previously. I think both will keep water out now.

Thanks again.
Old 12-04-02, 09:14 AM
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I've had to replace vent stack collars for a lady whose house was less that ten years old. The rubber sealing material just deteriorated due to exposure to the sun, I suppose.

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