Who do ya call when your neighbor's waste pipe won't get it out?

[dmccarty]

I would not want the vent in the attic due to the gas....

Later,
Dan

 

[MrJimi]

I would not want the vent in the attic due to the gas....

Later,
Dan

I would be happy if it was vented in HIS attic
Summers coming LOL
Jim

 

[Highbeam]

There is the big stack vent that should vent the sewer main and lateral and then there are the little vents at the end of each lateral. These little vents function to prevent a suction/siphon when a huge slug of water drains out of a fixture. Imagine a straw full of water with your thumb over it. The trap in your sink is the thumb and if the suction of the slug of water traveling down the drain line is too great it will suck the water right out of the trap which leads to sewer gasses entering your sink. The little vent lines only need to suck air and becuase of this you can put them in the attic with a one way valve on it. If it vents to the roof and you don't put a one way valve on it then some sewer gasses can make it out. There should always be the one big vent though with a stronger draft.

There is a fancy name for that one way check valve. You see it used in kitchen islands with sinks since there is no way to vent that fixture to the roof.

 

[N80]

They are called 'air admittance valves', 'cheater valves' or 'Studor' valves. As mentioned, no gas in the attic since it is one way. It only draws air. Besides, my attic is well vented...for various reasons both intentional and otherwise.

I'm no plumber by a long shot but given the simplicity of my set-up (two sinks, one toilet, one shower/tub on a septic tank) I don't see the need for anything that vents out. And for whatever reason, code doesn't call for it. And everything drains very well. So far, no problem with water leaving the traps.

I do wonder what would happen in the summer if it was real dry and we didn't use the place for a long period. I guess the traps could dry up and then gases could get in. So far that hasn't happened.

 

[scott_vt]

Methane is an explosive gas; an ignition source could lift that house off its slab! Hummmmm, now lets think!

 

[Highbeam]

Well N80, a septic tank digests poo and as a byproduct makes a particular amount of methane and other gasses. Without a vent, there is enough pressure made by this gas production to raise a roof... literally. I have actually walked on the floating roof of a poo digester at a sewer treatment plant. They harvested the gas to heat the poo which accelerated the decomposition. Anyway, the gas from the residential septic process typically vents back upslope through the house and out the stack vent. If you have no stack vent on your roof then where does the gas go?

Studor valve, that was the fancy name I was thinking of.

 

[N80]

If you have no stack vent on your roof then where does the gas go?

Good point. I don't know the answer or why the plumbing inspector passed it.

Technically, if the septic tank is making pressure from methane it is either venting back up through the water in the traps and into the cabin, or it is venting around the edges of the septic tank lid into the soil outside. Since there is never any odor in the cabin at all, I don't think it is coming into the house. So, either it is venting around the septic tank lid (which is just a concrete slab with no special seal) or a two bedroom rated septic tank just isn't making enough methane to matter.

 

[Highbeam]

Do you think it could make it out to the drainfield? Straight methane is odorless and colorless but generally it is accompanied by some other things like sulfur components that allow you to smell it. Thanks for your input N80, especially the studor valve in the attic.

 

[N80]

I think it would come into the house before going to the drainfield.

I got curious about this and asked a septic system expert who echoed much of what you said. Although he did mention specifically that methane can vent through septic tank lids that do not have rubber gaskets, which mine doesn't.

He mentioned the risk of methane collection in the house with a risk for explosion. This seem unlikely in my case. The attic is well vented (end vents, ridge vent, soffit vents).

But, I try to do things right so even though I don't seem to have a problem, I'm going to try to figure out a way to vent things properly (which up until now I thought I had....for all the grief the inspectors gave me, why did they miss this?!?).

In any case, thanks for explaining things.

 

[Highbeam]

You're welcome N80, while poo is indeed my bread and butter (I love saying that) there is always a practical side to the academic theories that they teach us. Your attic may be well ventilated but that studor valve only allows air to be sucked in. The non gasketed lids must be the tapered concrete type that are buried right? I would think that pressurized gas would be more likely to escape through the drainfield.