Pre remodel plumbing question

[skylarkguy]

I'm about to start a remodel on our master bathroom. It is on the ground floor with a second story above. The current drain plumbing is vented with 4 inch galvanized pipe that runs out of the crawl space up through the bathroom area to the roof. Unfortunately it is within the envelope of the space into which I will enlarge the bathroom. Can I replace the 4 inch vent pipe with multiple 1.5 inch ABS plastic pipe in order to move the pipes inside a wall? I'm hesitant to move the roof penetration because I just put on a new roof this summer.

on a related but different note. I bought a very nice used soaking tub..nearly 10 years ago to use in this space. Can't for the life of me get it to fit in the space though...so i have a 72 by 40 inch drop in tub for sale....

 

[Deere Dude]

Four inch seems kind of big for a vent anyway. It just lets air in so the fixtures drain smoothly. With multiple small ones I think sealing the top from the weather could be problematic. I would try a pvc 3" which should fit in a 2x6 wall for sure and maybe a 2x4 wall.

 

[RedNeckRacin]

There are specs in the IRC that will tell you what the minimum size is based on the fixtures that you are trying to drain. I would do my best to try and follow those guidelines. I am using the 2009 International Residential Code to build my house currently.

 

[/pine]

3" pipe will fit in a standard wall...it's done all the time...get a 3x4 coupling(s) and use a short piece of 4" plastic through the existing roof boot...

 

[RNeumann]

I’m smelling a rat on this one. I’ve never seen a 4” vent in a residential setting- except in specific areas that have snow loads and local AHJ adds the language.
As stated above the vent size is based on fixture units. An entire house can usually be vented with one 2” vent- based on fixture units.
Comments- don’t decrease and then increase pipe size. There is no code provision or reason to do so. It’s bad to do!

I believe you are missing something or not understanding what’s going on. Take another look at what’s going on there.

Question- how many vents does the place have? Look on the roof and see. It would be common to see one over the kitchen and then, depending on layout, to see a few more for bathrooms and the laundry. The only exception would be as noted above for some areas with snow.

Could the 4” be 3”?

Could the 3-4” pipe be just a few feet into the attic and the rest be smaller pipe?

 

[dadster4]

3" vent is all you need for up to three baths, increasing to 4" at the roof is for protection from frost build-up in the winter so the opening stays large enough above the roof.

 

[skylarkguy]

I’m smelling a rat on this one. I’ve never seen a 4” vent in a residential setting- except in specific areas that have snow loads and local AHJ adds the language.
As stated above the vent size is based on fixture units. An entire house can usually be vented with one 2” vent- based on fixture units.
Comments- don’t decrease and then increase pipe size. There is no code provision or reason to do so. It’s bad to do!

I believe you are missing something or not understanding what’s going on. Take another look at what’s going on there.

Question- how many vents does the place have? Look on the roof and see. It would be common to see one over the kitchen and then, depending on layout, to see a few more for bathrooms and the laundry. The only exception would be as noted above for some areas with snow.

Could the 4” be 3”?

Could the 3-4” pipe be just a few feet into the attic and the rest be smaller pipe?

Hopefully no rats will be smelling up the place. It is definitely a 4 inch pipe. This summer I re-roofed that section of the house. There are 4 pipes exiting the roof. a 4 inch, 2 1.5 inch, and a 2 inch.

This section of house was originally built in 1936, and was added on at least twice. I believe I'm working primarily in the original section. (oldest). The 4 inch pipe travels up from the main sewer line from the crawl space, makes a bend of about 22 degrees, then makes a steeper bend then back to plumb before exiting through the roof. When I roofed the house this summer I cut out a chunk of the cast iron and coupled in some black ABS pipe so the roof flange would seal on a nice fresh surface...and that should facilitate changing the pipe now.

 

[EddieWalker]

I’m smelling a rat on this one. I’ve never seen a 4” vent in a residential setting- except in specific areas that have snow loads and local AHJ adds the language.
As stated above the vent size is based on fixture units. An entire house can usually be vented with one 2” vent- based on fixture units.
Comments- don’t decrease and then increase pipe size. There is no code provision or reason to do so. It’s bad to do!

I believe you are missing something or not understanding what’s going on. Take another look at what’s going on there.

Question- how many vents does the place have? Look on the roof and see. It would be common to see one over the kitchen and then, depending on layout, to see a few more for bathrooms and the laundry. The only exception would be as noted above for some areas with snow.

Could the 4” be 3”?

Could the 3-4” pipe be just a few feet into the attic and the rest be smaller pipe?

4 inch cast iron is very common for venting around here in East Texas, and back in the SF Bay area, where I grew up. Remember that not to long ago, cast iron was used all the time, and it's very course on the inside, so "stuff" doesn't flow very well. Toilets also used to flush several gallons at a time. All that water, in that slow moving pipe, meant you needed a really big vent pipe.

I see 1 1/2 inch vent pipe used all the time for sinks and showers. For an older toilet, I would go with 2 inch. If it's a new 1.3 gallon toilet, you will never notice the difference between 2 inch and 1 1/2 inch vent pipe.

 

[RNeumann]

Ok, first post says galvanized and the second says cast iron- minor difference in the big picture but it helps me understand. I’m guessing the “rat” is the remodel. The 4” line could have been an old vertical stack that was later abandon in favor of the other vents- this probably occurred with the remodel.
With all those other vents on the roof this vent can’t be serving that much. Verify it’s not serving over 24 fixture units- that’s like 3 full bathrooms, a kitchen and laundry. Just google “plumbing fixture units” if you want to verify the numbers for each fixture. If it’s not over 24 units, cut the cast/galvanized pipe down in the crawl and run a 2” line to the roof from there. Since you have already done roofing I’d switch the roof jack to a 2” as well-going back to 4” isn’t code.
ABS or PVC is fine- I like ABS. Use the correct fittings- 4” no-hub coupling, little piece of 4” ABS, 4” ABS coupling, 4x2 ABS bushing reducer and away you go with the 2” ABS.

As a technicality- I believe your area is using UPC instead of IRC. They have a few differences regarding fixture units. They also have differences with AEVs and island vents. Some of that stuff is hard to change for the inspector.

 

[/pine]

... I cut out a chunk of the cast iron and coupled in some black ABS pipe...

This is a new, old school tactic used by architects/contractors with an eye for aesthetics when PVC became the norm... Black ABS stacks look much better than the bright white PVC...especially against a dark shingle roof etc...worked with one architect that would never allow a vent stack on the front (curb side) of a roof rake.