I am retro fitting a laundry room in a 200 year old house. The existing drain is not vented. It will be close to impossible to install a new vent trough the roof or to tie into the existing vents in the new addition on the house where the kitchen and baths are located. Are there another ways to vent the system? The laundry room is on the first floor and I'm running new pipes in the wall from the full cellar below.

Hi Coldspring...

You can add a mechanical vent... also called an air admittance valve or AAV... see images. The vent needs to be accessible so you can't hide it in the wall or if you do you must have an access panel so you can access and change the AAV out if it fails in the future.

MARK

Thanks Mark,

I see from you sketch that the AAV must be down stream from the P trap for the washer and it also looks like it must be higher than the stand pipe so I can't hide it in the cellar below. I most likely then will add it to the horizontal run and install it in another wall about 6 feet from the washer. If I were to to a laundry sink next to the washer could the one vent handle them both.

I should elaborate further on my system. The 2 inch laundry drain will run approximately 12 feet and tie into a 4 inch drain in the new addition. This drain is properly vented through the roof. Would that vent be enough for the laundry room or should I still add the AAV? If I install the AAV where I'm thinking then it will only be about 6 feet from the 4 inch drain.

Actually, the AAV can be a minimum of 6" higher than the trap. I usually put it at the same height as the standpipe...;)

You want to install the AAV within 5 feet of the washing machine PTRAP. The AAV will work for both the washing machine and a laundry sink, but I would install it at 42" off the floor if you use it for both fixtures... see image below.

I also recommend that you install a 2" test tee for a cleanout as near to the trap as possible.

MARK