the Q is about the lip, called the shower threshold. if there is no visible threshold, it means the shower pan holds very little water when the drain is blocked. this is not permitted. it is not code allowed. except if the space is sunk into the slab (or subfloor) and can hold a lot of water without a lip. this will not be your case since it's only a tub sized space. i don't know the numbers so that is as much as I can say about sizing to avoid having a threshold. -- if you had no shower threshold, you would just roll in to the shower. to build a shower without a threshold, you could share the drain burden over two drains by installing a floor drain in the bathroom. to get a floor drain in the bathroom, you could remove one of the two toilets you have, and rebuild the toilet drain to become a P trapped drain. to do this you will need to hire a master plumber. then, if you manage to place the entrance to your shower right where the drain is you will be in luck. the drain is the lowest part of the shower floor. from the drain, the floor slopes 1/4" higher per foot from the drain. the farther away you are from the drain the higher the "speedbump" will be. a channel drain, a long line, is great for making a flat (sloped not level) floor inside the shower pan. otherwise, a small drain forces you to slope the floor in an inverted cone in the shower pan the cone shape can be made of four flat triangles or it can be a continuous cone. -- but, doing so implies that your bathroom now becomes a "wet room" and so its marble threshold separating it from the corridor now becomes officially a threshold itself. since the bathroom is larger than a shower, if it ever flooded it could hold more water before the flooding spread to the rest of the building. /therefore you could arguably have a much lower bathroom threshold than the normal shower threshold. -- flooding can easily happen. an everyday example is if someone flatfooted blocks the drain for a few minutes just to get more heat, more sensation, or whatever. Then, if they get distracted, water will simply pour out of the shower pan. /another example is when someone leaves a wet towel in the bottom of the shower pan, and gets distracted (like leaving the shower to answer the phone). /another example is if someone has a medical problem and is unable to turn off the shower, and the drain could be blocked by anything including by themselves. a channel drain has less of this problem. it is harder to block since it is bigger (longer). -- it may be most practical to keep the 2" threshold. -- if you keep the threshold, you have to get up and over a 2" lip. the rise to the 2" height could be gradual. the threshold is not required to be constructed as a vertical obstacle; it can be a rounded out bump or a sloped bump. raising the entire bathroom floor a little bit will help you approach the threshold. inside the shower pan, sloping to a channel drain located on the farthest wall will help you make the threshold into a speedbump shape. -- everything i have written above is partial information. there is more to know. in addition to all that i have not yet written, there is a lot of other information that i don't know and which will be important to your specific case. there are inevitable corrections to what i have written above. take no action based on having learned anything in this post. get other information from other sources. consult local authorities too. -- since you are in a concrete condo, your bathroom has a dropped ceiling with your upstairs neighbor's drain pipes in that space between the ceiling drywall and the slab above you looking at it, you will see the same drain pipe configuration as your own drain pipes underneath your bathroom floor. this will enable you and the plumber to understand what could be done if you want to make changes. you have the right to access your downstairs neighbor's condo for this purpose just as he or she has he right to access their downstairs neighbor's condo for this purpose also. since it's a 20 storey building I'll assume the people managing the building know this already. making it a positive experience means you only hire the best Master plumber for any of this DWV work and you give a surprise gift to the downstairs neighbor at the end. -- hth /d

Thanks, I will have to post the layout tomorrow bc it's an odd portion of the house with lots of angled walls and such. There is a closet on the other side that is a very strange shape and I'm having trouble figuring out what part of it is behind the shower wall. So if we were able to steal some space from that closet, how many inches would be sufficient? The article said minimum 30" for shower, but it seems like that would be really uncomfortable. Would 34" work? This is a kids' bathroom, but still, 30" seems so tiny.

I converted a tub/shower combo in my high rise condominium and had to replace the drains. I don't know if this was because of the size of the drains or because of the condition of the drains but since the plumbing was original to the 1965 build I thought it better to get new stuff insofar as possible during this gut remodel. The drains needed to be accessed through my downstair neighbor's ceiling as you can visualize the common plumbing lines stack up on top of each other. It wasn't a difficult procedure but I needed access to my neighbor's apartment. If access to the drain from your neighbor is necessary, then ask your manager what the procedure is. In my building, we are permitted access but obviously have to pay for the costs of closing it up. It cost me about $1000 for my GC to open up my neighbor's ceiling and then patch and paint it again. It also cost me $2000 to have the water shut off when my plumbing was done - all of these expenses are why remodels in metropolitan areas become so pricey as it starts to add up - not to mention the regulations on working hours; the time it takes stuff to be brought up and down in the elevators - demo of my relatively small unit took about a week because everything had to be carried out - and of course you also need to make sure that all the common area floors are covered to avoid damage to the flooring :-)

Thanks for the input. I just measured my master shower door and it's 28.5". I think I will plan for a 26" door, swinging inward and outward. I like the idea of the pony wall being a little bit longer and just leaving the 26" space for the future door. My contractor is very thorough and will be sure to block for a door and grab bar to be installed in future if desired. Definately will put the controls in the pony wall like we did in master. The depth of the room right now is 64" from the current finished shower tile to the wall. So without encroaching on the 30" space for the toilet, we could get a 34" depth shower. That's still pretty small, but don't see a way to make it deeper without expanding the scope and $$ by stealing space from adjacent attic. If money were no object we would look into doing that. I'll ask the contractor about it, but I don't think budget will allow.