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Pipe leak phobia

jklingel | Posted in Energy Efficiency and Durability on

Fairbanks, AK. HDD = 14,000. We will soon be adding a 2-story addition to our 30 yr old house. I will have 12″ walls, either double-stud or Riversong/Larson Truss, with dense-packed cellulose.

Question, regarding the drain waste vent system in the second floor, living area: The incoming water will be inside the vapor barrier at all appliances. My concern is with the DWV system, which will have to run for several feet along an outside wall. Code here allows pipes within the first 1/3 of the wall’s R value, but I don’t like pipes in exterior walls. For one, I would like them accessible in case of leaks. Ignoring the extra cost, is it a bad idea to build yet another wall inside the VB just to run the DWV system and electrical in?

If I use the Airtight Drywall Approach on the inner-most wall, will I be generating any “issues”? I would not be sheetrocking against the vapor barrier in this area, and don’t see how moving the sheetrock 4″ from the VB can cause any harm, if air sealed.

Fire away. BTW: I am trying to move appliances so the DWV system will run in interior walls, but that will likely not happen completely.
Thanks. john

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  1. GBA Editor
    Martin Holladay | | #1

    Assuming you don't mind losing the interior space, and you don't mind the added expense, I see no reason why you shouldn't build a frame wall to hold your drain pipes.

    It's also possible to detail your polyethylene vapor barrier as the air barrier, using Tremco acoustical sealant at the seams. (Seams should be planned to occur over framing, so that the seams are sandwiched between a stud and a furring strip or another stud.)

  2. Steve El | | #2

    Would code let you those pipes and wires in some built in cabinetry or shelving units? A floor to ceiling flat wall is useful if you have artwork to hang, but less useful if you need book shelves or cubby holes.

  3. David Meiland | | #3

    Seems to me your situation is similar to one where you'd build a stud wall against a concrete wall in order to run pipe and wire. Question is, can you do it in your project without punching a bunch of fastener holes in your drywall? Likely not a problem but I would give it some thought.

  4. Kopper37 | | #4


    Have you considered soffits and built-out structures to house the DWV line(s)?

    I've lived in several older houses that were built in the era before indoor plumbing. With the advent of well pumps and toilets, the plumbers often ran the DWV pipes on the outside of the wall cavities, exposed (sometimes the cast iron pipes were too big to fit inside the old stud cavities).

    Remodelers often hide these exposed pipes. The horizontal legs are covered with a soffit, vertical sections in a bump-out (think of a vertical soffit).

    It's another option anyway . . .

  5. J Chesnut | | #5

    Are you concerned with leaks in the drain and vent pipes? I haven't come across this as a problem.
    Supply pipes I would imagine are relatively easy to run through the floor to stay out of the exterior wall.
    Vent and drain pipes in the exterior wall, particularly a 12" exterior wall, don't seem risky to me.
    I'm an architect though so I may be missing something here.

  6. Riversong | | #6


    If you want to keep the DWV system out of the thermal envelope and accessible for service, then I would suggest keeping it entirely inside of the air/vapor/thermal barriers. In other words, do as several hear have suggested and design clever soffits and chases that can become architectural features.

    For instance a soffit to suspend the kitchen wall cabinets can house pipes and/or range hood ducting. Vertical chases can be made of wood (screwed together for access) and can be the sides of open shelving units in bathrooms or frame the medicine cabinet or toilet. Of course vertical chases can be enlarged to become interior stub walls for privacy or to create nooks.

    Endless creative possibilities.

  7. Riversong | | #7

    I should add that, when I design floor plans, I'll often stack closets so that DWV or radon vent piping can run up a corner of the closets (inside a chase).

    And, by the way, one of the problems with plastic DWV piping is that it has no sound deadening properties and many people don't like to listen to the toilet flushing when they're sitting in the dining room. So, if you build chases, you can stuff them with insulation for sound-proofing.

  8. jklingel | | #8

    Martin: Thanks. I will definitely Tremco the VB, or whatever goo is compatible w/ it. I ordered some stuff called Tuff Nuff, if I recall, and their tape. I will inquire about what goo is compatible w/ it. I am a little concerned about the stuff, btw. When it arrived, I found it to be very tough, but brittle. If you cut it, you can tear it at the cut fairly easily. I’m not sure I like that.
    Steve: None of either will be needed in the laundry or bathroom, but thanks for the thoughts.
    David: Good thought, but I don’t think there will be many fastener penetrations in the area of concern. I will goo the ones there are.
    Daniel: A good idea if it were not so cold here. I have to insulate my present DWV pipe where it exits the roof, and still I get some rather artistic Ice ghosts forming on it. Before I insulated it, I had it freeze shut a few times.
    J Chest: I agree. The more I think about this, the more I think I am over-thinking it. HTH is a vent pipe going to leak? Only if I completely forget to glue a joint, and even then it may not. I was re-plumbing copper lines when my neighbor bought another neighbor’s house, marveling at how those seriously boogered solder joints actual held pressure. Then I found one where he actually never even soldered! How it held pressure I have no idea.

    The vent pipes will go in the exterior wall, unless I get permission to rearrange appliances and run them in interior walls. I have bigger things to worry about. Thanks for the brain adjustments

  9. jklingel | | #9

    Robert: I posted before your comments arrived; electrons travel slower in the cold. As always, thanks for the ideas.

  10. Riversong | | #10


    I imagine you're on dial-up on a party line ;-)

    Oh, by the way, one way to control vent pipe freeze-up is to enlarge the diameter before exiting the roof - and use black pipe (or flat black paint) to let the sun warm the stack.

  11. jklingel | | #11

    Robert: I used 3" black ABS, but it is not insulated in the attic once is exits the cellulose. I should get in there and foam it. Next time I will increase to 4". Thanks. john. BTW: Sun? It pokes its head up for 3 hrs 45 min near Christmas, and obviously at a very low angle. It is not real effective at warming us up then, esp when the temps are typically below zero all day.

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