Perhaps we’re each familiar with different codes or perhaps they do things differently where you are?

I spent 4 years as a commercial superintendent on various projects in the Caribbean, Dubai, and the DFW.

None of those projects would have any difficulty adding plumbing wherever they wish.

Every place I've ever lived had plumbing in the walls. Now, it also had it in the floors, so your point is well taken. But I seriously doubt that a central plumbing stack is a serious holdup on plumbing out an entire floor.

Then again, I don't have any real experience, so I'm very much being optimistic here without actual hands-on knowledge. I could be very wrong, and would love to hear why!

So, this is me reaching back aways in memory. Walls with plumbing through them are held to different standards to other walls. Walls with plumbing use 2 by 6s. Builders and architects try to optimize by making as few walls as possible walls with plumbing because they are more expensive. Your regular walls use 2 by 4s.

So yes, some walls have plumbing running through them, but not all. Any architect and contractor will try to optimize cost by having as few walls as possible with plumbing. Which is why in some apartments, neighboring bathrooms in units will be close or share some wall space.

I've never seen a wall framed with 2x6s because it had plumbing in it. It's all 2x4 regardless, here—you almost never see a 2x6 wall. Is that a California thing?

The most common example is a wall with a toilet drainpipe. In the US, that requires a 3" inner diameter pipe - the outer diameter is 3.5", which is exactly the same as the space inside a 2x4 wall, but if you need any fittings, it won't fit, and even if you don't, the likelihood of being pierced by nails is too high when the pipe is right against the drywall. If you have a single-story house, there would be no need for such a drainpipe, so this is primarily an issue in multi-story buildings. Sometimes there's a central chase that contains these pipes (as well as HVAC ducting), but unless all your bathrooms surround that central chase, you'll need a 2x6 wall somewhere.

As far as I know, no. I learned about this when I lived in North Carolina. The house I grew up in had 2x6 wet walls with all other walls being 2x4.

It could be state or local building codes based. Here is a mention of it from a city in Illinois. But it definitely isn't just a California thing.

https://elmhurst.org/DocumentCenter/View/1826/Plumbing-Requi...

https://www.reference.com/world-view/standard-wall-thickness...

> I've never seen a wall framed with 2x6s because it had plumbing in it. It's all 2x4 regardless, here—you almost never see a 2x6 wall. Is that a California thing?

My California home is all 2x4s everywhere and there's plenty of plumbing in most walls.

> Every place I've ever lived had plumbing in the walls.

In every wall and under every floor? How many sinks did you have?

Sorry, I wasn’t clear. Every house had plumbing in the walls & under the floor, but not in every wall. Normal houses, not.. a showroom for fountains!

I see plumbing exposed in the ceiling in some of the cool fancy new lofts that were converted from offices (in NYC).

Yeah but your ceiling is the next level's floor. If drilling a 4" hole in the floor/ceiling to accomodate a toilet drain is too damaging to the structural integrity (not sure I believe that, but I'm not an engineer) then it's a non-starter.

Maybe you could build the bathrooms and kitchens along partition walls that have space behind them, so pipes could run above the floor, between walls, to the building core where all the main plumbing was designed to be.

> Yeah but your ceiling is the next level's floor. If drilling a 4" hole in the floor/ceiling to accomodate a toilet drain is too damaging to the structural integrity (not sure I believe that, but I'm not an engineer) then it's a non-starter.

It isn’t, it’s called core drilling and it’s extensively used in commercial buildings with concrete decks for electrical conduits, electrical poke-thru devices, plumbing pipes, hot water/chilled water piping for HVAC, data cable sleeves, fire sprinkler piping, etc.

A typical commercial building floor is concrete in a metal pan that has tensioned cables in the concrete to reinforce it. A few holes aren’t going to ruin the structural integrity. A ground penetrating radar scan should be performed prior to drilling to avoid cutting the cables, if you cut one of those, then the structural integrity is affected and repairs get expensive.

A 4" or 6" hole won't be a problem. In fact, if you go to any commercial project you will probably find more than a few holes that shouldn't have been drilled because there was an over eager mechanical employee or someone who could not read plans properly. Those holes are often just covered up.