# Plumbing vents on houses **URL:** \ **Category:** Factual Questions\ **Created:** [May 14, 2007, 4:41pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059 "2007-05-14T16:41:17Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Shai\_tan](https://avatars.discourse-cdn.com/v4/letter/s/f4b2a3/32.png) [@Shai\_tan](https://boards.straightdope.com/u/Shai_tan)\ **Post date:** [May 14, 2007, 4:41pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/1 "2007-05-14T16:41:17Z")
I am looking at buying a two-bedroom built in the early 20’s. One of the previous owners completely rehabed the house and its seems to be in pretty good shape. But the house inspector I hired mentioned that she couldn’t find the main vent (for plumbing). Its my understanding that it generally runs straight up to the roof from behind the toilet (It only has one bathroom). Regardless of where though, it should exit the roof at _some_ point. My father-in-law is acting as my agent (he is also a contracter, so fairly knowledgable) and assures me that there _should_ be a vent exiting the roof. Our concern is that when the roof was redone a number of years ago, that the vent was cut and accidently (?) covered over. The inspector mentioned that she had never seen a house with circular venting, but said that it didn’t mean she wasn’t standing in one. Is it possible that the house is still vented (safely or properly) without a visible vent exiting the roof? We went through the attic and could not find any evidence of one or where one used to be. If the main vent _was_ there, and is now covered over, then sewer gases could be venting _into_ the house, right? The current owner sent his contracter through the house, and agreed to fix pretty much all I wanted done, but he didn’t see a vent either. He didn’t think it was a problem. He’s been renting the house for years and the plumbing seems to be working fine. The deal is in almost done. I need to act quickly if I want something done or want to back out. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [May 14, 2007, 4:51pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/2 "2007-05-14T16:51:39Z")
[QUOTE=Shai’tan] He didn’t think it was a problem. [/QUOTE] Well, of course he doesn’t. He’s trying to sell you a house. I wouldn’t under any circumstances go any further until you can find a plumber/inspector/engineer who can assure you that the plumbing in this house meets whatever applicable codes are in effect, or barring that, that it is properly vented. Are you sure there’s a **GQ** in this? ---
**Author:** ![Shai\_tan](https://avatars.discourse-cdn.com/v4/letter/s/f4b2a3/32.png) [@Shai\_tan](https://boards.straightdope.com/u/Shai_tan)\ **Post date:** [May 14, 2007, 5:03pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/3 "2007-05-14T17:03:43Z")
GQ? Yes: Is it possible for the house to be vented, without it exiting through the roof? If so, then how? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [May 14, 2007, 5:16pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/4 "2007-05-14T17:16:33Z")
[QUOTE=Shai’tan] GQ? Yes: Is it possible for the house to be vented, without it exiting through the roof? If so, then how? [/QUOTE] It might vent into the attic, but that’s probably not to code. ---
**Author:** ![FordPrefect](https://avatars.discourse-cdn.com/v4/letter/f/e99b99/32.png) [@FordPrefect](https://boards.straightdope.com/u/FordPrefect)\ **Post date:** [May 14, 2007, 5:17pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/5 "2007-05-14T17:17:39Z")
There is fitting that allows you to build a cheater vent. Basically it’s a spring loaded valve that only lets air into the line. I have one in my master en suite for the sink, because we wanted it in a place that wouldn’t allow for a vent stack through the ceiling. But to run a whole house on one or more cheaters? Never heard of that, but it would be better than all that methane building up in the attic… ---
**Author:** ![NurseCarmen](https://avatars.discourse-cdn.com/v4/letter/n/5daacb/32.png) [@NurseCarmen](https://boards.straightdope.com/u/NurseCarmen)\ **Post date:** [May 14, 2007, 5:20pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/6 "2007-05-14T17:20:56Z")
Venting isn’t that important. Until your bathtub fills up with shit. I would stand pretty firm on the need for one. ---
**Author:** ![KneadToKnow](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kneadtoknow/32/3999_2.png) [@KneadToKnow](https://boards.straightdope.com/u/KneadToKnow)\ **Post date:** [May 14, 2007, 7:16pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/7 "2007-05-14T19:16:28Z")
[QUOTE=Shai’tan] GQ? Yes [/QUOTE] Sorry, I missed it. ---
**Author:** ![A.R.Cane](https://avatars.discourse-cdn.com/v4/letter/a/ee7513/32.png) [@A.R.Cane](https://boards.straightdope.com/u/A.R.Cane)\ **Post date:** [May 14, 2007, 7:37pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/8 "2007-05-14T19:37:35Z")
There must be a way for air to enter the system w/o going through a fixture. Every fixture has a trap of some kind, to provide a water barrier between the sewer and the living space. The only “circular” venting I’m familiar w/ is limited to one, or two, fixtures, such as installing a kitchen sink under a window. These are limited, by practicality, and by code, to five feet or less. There has to be a vent somewhere, or one, or more, of the fixtures will act as the vent, allowing air into the system and breaking the barrier, thereby allowing sewer gases into the building. Get a professional plumber, or plumbing inspector, to check this out before you buy. It could be an easy fix, or it could be very expensive. ---
**Author:** ![danceswithcats](https://avatars.discourse-cdn.com/v4/letter/d/9e8a1a/32.png) [@danceswithcats](https://boards.straightdope.com/u/danceswithcats)\ **Post date:** [May 14, 2007, 8:06pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/9 "2007-05-14T20:06:08Z")
[QUOTE=Shai’tan] GQ? Yes: Is it possible for the house to be vented, without it exiting through the roof? If so, then how? [/QUOTE] Yes, it is possible. Many older homes which had indoor plumbing introduced as an upgrade have the DWV stack running up the exterior wall, such that the roof, per se, isn’t penetrated. Most plumbing codes require that when those systems are upgraded, they be placed within the dwelling walls, even if a bumpout or pipe chase is constructed to enclose them. Then, they will penetrate the roof. ---
**Author:** ![Carson\_O\_Genic](https://avatars.discourse-cdn.com/v4/letter/c/cdc98d/32.png) [@Carson\_O\_Genic](https://boards.straightdope.com/u/Carson_O_Genic)\ **Post date:** [May 14, 2007, 8:07pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/10 "2007-05-14T20:07:11Z")
Don’t buy 'til you find the vent.Why? Even if you had no hazard from sewer gas-which there is- vents also allow warm moist air out their top from chimney effect.So wherever it terminates and can condense on cooler surfaces,it will.Why venting in the attic isn’t great,especially if it is insulated in the rafters.The area could be rotting and/or mold covered.Meaning possible structural damage. ``` FordPrefect metions an AAV (air admitting valve) which are usually within code for branches that are otherwise difficult to vent,e.g. island sinks.Not usually allowed for a main vent stack,but I cannot comment on legality in your jurisdiction. ``` ---
**Author:** ![Dinsdale](https://avatars.discourse-cdn.com/v4/letter/d/97f17d/32.png) [@Dinsdale](https://boards.straightdope.com/u/Dinsdale)\ **Post date:** [May 14, 2007, 8:54pm UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/11 "2007-05-14T20:54:13Z")
I’m with the folk who agree there’s gotta be a stack somewhere, and you’ve got no business buying this place until you find it. Recently read the book **Flushed** by C. Hodding Carter - an extremely interesting read on plumbing through the ages. Carter makes a pretty good case for soil stacks being the necessary “invention” with respect to making indoor plumbing universal, healthy, and odorless. ---
**Author:** ![DesertDog](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/desertdog/32/11503_2.png) [@DesertDog](https://boards.straightdope.com/u/DesertDog)\ **Post date:** [May 15, 2007, 4:14am UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/12 "2007-05-15T04:14:49Z")
[QUOTE=danceswithcats] Yes, it is possible. Many older homes which had indoor plumbing introduced as an upgrade have the DWV stack running up the exterior wall, such that the roof, per se, isn’t penetrated. Most plumbing codes require that when those systems are upgraded, they be placed within the dwelling walls, even if a bumpout or pipe chase is constructed to enclose them. Then, they will penetrate the roof. [/QUOTE] Why the prejudice against an externally-run vent? I’m thinking moist air might freeze in cold weather eventually blocking the stack. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [May 15, 2007, 4:41am UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/13 "2007-05-15T04:41:22Z")
In San Bernardino Country, CA, at least, one vent is required near each trap on the output side so as to avoid siphoning the trap dry. I would agree about not doing anything until a plumber or inspector that you hire says that the plumbing meets the local building code. ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [May 15, 2007, 11:30am UTC](https://boards.straightdope.com/t/plumbing-vents-on-houses/404059/14 "2007-05-15T11:30:09Z")
If you need to make a fast decision, you can always have the current owner sign a contract at closing indicating that he’ll take care of the problem upon discovery or after closing. Have a lawyer make sure all the words are nice and tight and binding.