I have a flat roof with easy access and a wall around it which I've started to use to grow vegetables in pots. The problem is that two of the three 4" diameter cast iron vent stacks, which terminate 3 feet above the deck surface, sometimes emit foul odors (as they are designed to do, right?). Can I extend them upward above nose level? Can I do this by fitting 3" plastic inside the existing pipe or should I get 5 1/2" plastic to go outside them? Plastic seems easier than adding cast iron.

Or maybe there is some neat way of solving the foul odor problem without extending the stacks??

Any suggestions would be most appreciated.

I have a flat roof with easy access and a wall around it which I've started to use to grow vegetables in pots. The problem is that two of the three 4" diameter cast iron vent stacks, which terminate 3 feet above the deck surface, sometimes emit foul odors (as they are designed to do, right?). Can I extend them upward above nose level? Can I do this by fitting 3" plastic inside the existing pipe or should I get 5 1/2" plastic to go outside them? Plastic seems easier than adding cast iron.

Or maybe there is some neat way of solving the foul odor problem without extending the stacks???

Any suggestions would be most appreciated.

I might just have what you're looking for. They're called "Odor Hogs" (see image) Check them out at; OdorHog(tm), roof vent pipe filter that stops septic tank odor. 1-800-963-6746 (http://www.odorhog.com/?gclid=CPnf4sK-so0CFQiIgQodWlY5vA)
Good luck, Tom

I might just have what you're looking for. They're called "Odor Hogs" (see image) Check them out at; OdorHog(tm), roof vent pipe filter that stops septic tank odor. 1-800-963-6746 (http://www.odorhog.com/?gclid=CPnf4sK-so0CFQiIgQodWlY5vA)
Good luck, Tom

Tom, thanks for the suggestion. The charcoal caps you suggest might help but they are more expensive and require more maintenance than Studor Maxi-Vent Air Admittance Valves. Also, based on experience with activated charcoal odor removing systems, they can significantly reduce odors but some portion of the stink is not adsorbed. The one-way valve seems a better solution.

Code calls for a AAV to be placed at least 6" above the flood rim o0f the fixture it's venting. It also mandates that the AAV must be located in a assessable location On top of the roof is not a assessable location. If a AAV's install inside a wall a access panel must be placed so it can be serviced. Regards, tom

Code calls for a AAV to be placed at least 6" above the flood rim o0f the fixture it's venting. It also mandates that the AAV must be located in a assessable location On top of the roof is not a assessable location. If a AAV's install inside a wall a access panel must be placed so it can be serviced. Regards, tom

Dear Tom,
If you read my original request for advice, you'll see that my roof is so accessible I am there every day tending my vegetable garden and that's why the smell from the vent stacks is occasionally intrusive. It's easier to walk up the spiral staircase to the roof patio than it would be to open a wall access panel. And yes, I did read the Code for the AAVs when I learned about them. But thanks anyway.

Sorry, I should have remembered the roof garden. I've never installed AAVs in a exposed location before but it should contain any odor from the vents. But if you wished you could couple a extension on and take the vents up overhead. Good luck, tom