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Old 10-22-2008, 02:28 PM   #1
Vince Rosati
 
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Vent dryer through flat membrane roof


Is it possible/legal to vent a gas dryer through a flat membrane roof?

Thirty years ago I built an addition, part of which has a flat roof. The addition made the laundry room an interior room, with no direct access to outdoors.

I ran sheetmetal 3 1/2 x 14 inch ductwork up through a wall, 90-degree turn at top, transition to 8-inch circular duct. Then a 45-degree angle, two more feet of circular duct, and finally another 45-degree angle to a through-the-roof vent cap. This worked for more than 25 years, with occasional cleaning of the vent cap.

Five years ago, the previous roll-roofing was replaced with a membrane. The contractor said it was illegal to vent the dryer through the membrane roof. (I think he didn't want to cope with flashing, etc.)

I believed him. I replaced the old ductwork with a 10-foot run of 6-inch corrugated (stretchable) aluminim circular duct through a small attic to the outside wall. Venting is finally through a louvred fixture. I clean the final fixture periodically, but it is getting harder for my old "slightly overweight" body to climb the ten feet to the fixture. Further, it is probably time to clean out the alluminum circular duct in the small attic. But getting to it will be painful.

Is there any reason to not go back to my original installation??

Thanks for wading through this saga.

Vince

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Old 10-23-2008, 06:13 AM   #2
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Vent dryer through flat membrane roof


Sounds like your contractor didn't want the extra work of flashing the penetration. I see chimney flues and generator exhaust stacks run through rubber roofs everywhere. What you have isn't a hot pipe by the time it gets to the roof. As long as the pipe is solid, there is no reason it couldn't be flashed. In case you'd have to, you can get a double walled, insulated duct to go through the roof membrane and flash to that.

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Old 10-23-2008, 07:22 AM   #3
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Vent dryer through flat membrane roof


Maintenance,

Thanks for the rely.

I agree, they didn't want the extra trouble.

My old installation had an outlet cap right down on the roof. Is that OK, or should I extend a "chimney pipe" up a few feet?

Vince
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Old 10-24-2008, 06:49 AM   #4
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Vent dryer through flat membrane roof


The outlet of the pipe should be 8 inches minimum above the finished surface of the roof.
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Old 10-26-2008, 03:02 PM   #5
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Vent dryer through flat membrane roof


Maintenance,

Great bit of info! Thanks very much. I guess the idea is to keep warm air away from the flashing and caulking.

Thnaks again.

Vince
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Old 10-27-2008, 06:13 AM   #6
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Vent dryer through flat membrane roof


Actually 8" is a standard NRCA number (National Roofing Contractors Association) and as far as I'm aware is for snow piling up around the penetrating item or rain splash.
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Old 11-02-2008, 02:11 PM   #7
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Vent dryer through flat membrane roof


Maint::

I have been away for a week and so did not get a chance to reply. Thanks for the added info. I appreciate that the various codes are based on good sense and I am glad to know the real reason for this one.

Best regards,

Vince

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