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L2L system using the same vent for both sewer and landscape lines?

 
Michael Sunnyvale
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Hi,

We are remodeling our house and have the opportunity to start our laundry room from scratch. All of the L2L systems we’ve seen drawings of use an AAV to vent the grey water line going to the landscape. It seems most of the drawings are to retrofit an existing laundry room. If I start from scratch and can install any necesssary venting within wall, etc, I’m assuming I can just install a standard vent that goes out the roof? Is this correct? The AAV isn’t strictly necessary. You just need to have a vent (whether its AAV or not), correct? I’m assuming the AAV is just particularly easy to install and retrofit.

Second, if I can use a non AAV vent, then could I just tie back into the vent for the line going to the sewer, so I’m effectively using the same in wall vent to vent both the sewer and the greywater line? The greywater line should vent properly to the vent, because the sewer line would be blocked with a p-trap. I’m a little worried though about the sewer line, because in theory the vent may activate, but it also may produce suction on the grey water to landscape line, and draw in moisture or soil on that end. That could be removed with a p-trap on the greywater landscape line, but I haven’t seen anyone put a p-trap on that side. Any thoughts?

 
Jay C. White Cloud
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Hi Michael,

Welcome...

If I start from scratch and can install any necessary venting within wall, etc, I’m assuming I can just install a standard vent that goes out the roof? Is this correct?


No, technically it's not (I can say 100% as I don't have your design blueprints or understand what your local "add on" codes might be?

I will give you a "back story" about AAV's. They are almost 100 years old in design but only got here from Europe about 20 years ago, or less. They were "fought against" by many in the "building trades" as we are also still resistant to many "global perspectives" on architecture...or certain systems...like metric as another example...

AAV's are actually a great idea, and now most plumbers love them. I would also point out that if any design can avoid creating another "roof penetration...then that is the design you want to go for. Placing "holes" of any kind in a roofs structural/weather diaphragm is a challenge to be avoided if at all possible. Roof penetrations add cost, and it isn't a matter of "if" but when they must be serviced/repaired. I would also offer that they will often leak and the property owner do not notice this until extensive interstitial wall damage has taken place...

We try to avoid "roof penetration completely if possible, other than for fire burn units and even then often "other arrangements" are always considered first...

Second, if I can use a non AAV vent, then could I just tie back into the vent for the line going to the sewer...


Probably not...Sewer venting has some pretty strict guidelines to follow so I would suggest show a code officer or plumber the plan to get their views of it...It's not just about "venting" but when and where in the line you can vent...what is being vented and how...

As for "traps" and "access service ports/clean outs" I add as many as the budget and design will allow. One the worst issues we have in "American Architectural design" is not attention to "disentanglement" which revolves around good planning for future servicing and maintenance....Plan now, with a little added cost and time to save big $$$ later and lots of headaches...

Regards,

j
 
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