How can I extend a 1.5" galvanized plumbing vent up a 6:12 pitch roof? Relocate to make clear area for solar

I'd like to extend the following plumbing penetration to a spot higher on the roof. At this time I have access from above to the pipe embedded in the wall, and access to the roof below the 6" dimensional rafters:

I'd like to stick with galvanized and with long sweep elbows if possible, to preserve the ability to snake the fixture from the roof if needed later.

6:12 pitch is 6 inches rise per 12 inches of run, or 26.57 degrees. The pipe comes up vertically, so we're interested in 90 - 26.57 = 63.43 degrees.

Will be inspected to California Plumbing Code.

Yet, there seems to be no 63.43 degree elbows made ;-)

• are you sure you don't want a 60 degree bend in that pipe, instead of 30 degrees? you have drawn and describe a roof with approximately 30 degrees pitch. – Jasen Sep 27 '19 at 23:35
• Corrected to 63.43 degrees, almost a 45 plus a 22.5. – Bryce Sep 30 '19 at 8:01

A pair of elbows of any angle can do the trick. For example, a 90 degree elbow can bend the vertical pipe so that it goes horizontally along the top of the wall. A second elbow connected to the first can redirect the pipe so it goes parallel to the rafter at any elevation/angle.

I gave the example with 90 degree elbows but the same principle works with a matched pair of elbows of any angle. The question is whether there's enough room to fit the two-elbow assembly. If it's done with 45 degree angle elbows then the assembly will be narrower, but also taller.

Depending on how important it is that the vent be moved, you could consider other approaches. It would be technically possible to make the vent stack go back down the wall, under the floor, and rise elsewhere as would be done for a sink in an island, or even to combine it with another existing vent. It may also be acceptable to replace the vent stack with an air admittance valve.

• That however would be a problem to snake through all four 90 degree elbows. AAV's are not allowed in my jurisdiction, and would be a bad idea just under the roof, where it could never be replaced once the rubber rots. – Bryce Sep 30 '19 at 8:01
• Why would you need to snake a vent? That's an extremely rare situation. Use a full-wrap no-hub clamp to convert to ABS as low as possible in the attic and you're good to go. – isherwood Sep 30 '19 at 13:18
• If an AAV were to be used it shouldn't be installed in the roof. It should be installed in a serviceable location such as a cabinet near the plumbing fixture for which the vent exists, and the remainder of the vent piping would be abandoned. It's a moot point, of course, since your jurisdiction won't accept AAV. – Greg Hill Sep 30 '19 at 17:11
• @GregHill and the piping is completely inaccessible, so a new vent cabinet would have to be built. For isherwood , while rare it happens, and doubly so for a vent that is otherwise inaccessible without tearing out walls. – Bryce Oct 1 '19 at 2:26

I chose to go with a suggestion from AskTheBuilder's Tim Carter, along the lines of @Greg Hill's answer. It unfortunately can't be done in galvanized due to the lack of a 22.5 degree fitting. But it can be done in ABS or PVC:

Now I just have to worry about PVC deteriorating in the sun. See Is PVC an acceptable pipe for a vent stack through the roof

With this layout I can add one more panel, and have a pleasing layout for the solar.

What about using flexible pipe for this section? Something like the Walker (46971) 1-1/2" Diameter x 6' Length Galvanized Flexible Exhaust Tube?

• Interesting, though no sure if that's going to be listed for plumbing use. Never mind it's a vent (no actual water except rain ever travels through it). – Bryce Sep 27 '19 at 8:49

6/12 pitch is 26.5 deg, not 22.5--so even if available I don't think that'd help you. Perhaps you could buy galvanized pipe and have a local welding shop create the 26.5 deg you need?

I don't know but suspect the flex would not meet code. Vents must be air/water tight so that sewer gas cannot leak into the home.

• The angle is irrelevant. As long as there's room in the attic, any reasonable angle can be used to traverse the distance. Also, pairs of 90s at each end allow literally any angle to be achieved. – isherwood Sep 30 '19 at 13:14
• Pairs of 90's can't be snaked very easy... – Bryce Oct 4 '19 at 4:51