I have 10 gpm flow (measured at a peak time...8am on a hot day). Any recommendations on using 1/2" vs 3/4" (option #1 or #3 above)? I like 1/2" because my hose bib and sprinkler heads are 1/2" and it's simple. Yet I like 3/4" since it gives room for expansion (though now unforeseen) and small extra cost. I just wonder if there are any potential disadvantages to using 3/4" in this application?

The setup took looking at a couple of times to get a sense of what was going on, so let me just clarify: The fixed shower head will be on the wall on the far left? and the handheld will be facing as you walk in? If I understand this correctly, then: We plan to use the hand-held shower to shower our daughter who is disabled. She will be seated when I shower her. We need to decide whether to install a corner bench in the back near the #3 studs or use a portable bench in the center of the shower closer to the # 1 stud. If we do the corner bench and place the slide bar on the #3 studs, I wonder if I will get soaked by the water coming toward me Although that is true what you say, I imagine that you would be standing inside the shower on the left side of the valve, if she were seated on the proposed seat, which should be fine for water on you- but wouldn't that mean that there will be water spraying out of the shower? If that is OK, then I would think that is the best option- no portable seat, nice fixed bench, and hand held above your daughter. But looking at the dotted line- does that give you enough room to get in and out of that shower? while assisting her? Will she be able to sit independently? In the corner, that doesn't give a lot of room, if you were to need a second hand? Will that ever be an issue? I can't judge the dimensions, but I would think a long bench along that far left wall would be better, but then the handheld would need to be over there? That would look a bit like the sample pic, I guess. Tell me what the setup is for the plumbing exactly and is it ok to move it....

Obviously Joeplumb is not a plumber... stitz crew, I commend you for your efforts in working out the WSFU formula. As you have learned, that system works very well for quickly computing a 2 or 3br single family dwelling in an urban area where the supply line is 150' or less but when confronted with a large load such as yours and a long service line it leaves a lot of questions unanswered. Given that you are an engineer I am sure you can appreciate if we take the time to actually engineer your line. First of all, let us list the code specs and the given information we have at hand. Code requires that when we design a water service line for a single family residential structure we must design for 100% duty cycle, meaning that the line must be able to supply the full gallon per minute supply & pressure to structure even when all fixtures in the structure are on at the same time. Allowable pressure at the structure water service "Main Water Shutoff Valve" is a minimum of 45psi and a max of 85psi. If the supply pressure is below minimum we have to install a boost pump and if above 85psi, even intermitently we must install a PRV (pressure reducing valve). The first step is to make a list of all the fixtures in the structure and use the code table to determine the GPM we are required to provide for each fixture. I did not have a list of fixtures for your house so I made a best guess based on the information at hand. You have 5.5 baths so for illustration I assumed one Master Bath(2lavs and both tub & shower), 4 standard bath groups & the 1/2bath So for the bathrooms we have i estamated; 7 lavs @ .5gpm = 3.5gpm 1 shower @ 3gpm 4tubs @ 4gpm=16gpm 5WC @ 3gpm= 15gpm Kitchen sink 2.5gpm Dishwasher 2.75gpm Wash machine 4gpm laundry utility sink 4gpm 2 hose bibbs @5gpm - 10gpm That adds up to a total combined load of 60.75gpm Now contrary to popular opinion, reducing the size of a line does not decrease the volume of flow, however as the line size is decreased the velocity of flow increases and the pressuree decreases exponentially from "Friction Head Loss"(pressure loss resulting from friction with the pipe wall). By example- if your 60gpm was flowing through a 6" pipe the velocity of flow and pressure loss would be 0.66ft/sec & 0.01si/100' but if you were to attach an 1-1/4" line the velocity in the 1-1/4" would be 10.71ft/sec and the pressure loss would be 11.18psi/100' Not only does the higher velocity result in pressure loss, it also increases the rate of pipe failure from pipe wall erosion. In an effort to minimize pipe wall erosion the codes limit the allowable velocity of flow to 8ft/sec in copper pipe & 12ft/sec in plastic pipe. Now let us begin putting it all together.(for your own enlightenment you may want to download a "Friction Head Loss Chart". They are placing your meter in a vault near the street. If we consult an friction head loss table an 1-1/4" line can handle 60gpm without exceeding the maximum flow rate and it is a short run from the municipal main to the meter (probably in the order of 10'). The friction head loss in 1-1/4" pipe would be 11.18psi/100' or 11.18psi/100 divided by 100 = 0.1118psi/ft x 10ft = a pressure loss from the main to the meter of 0.011psi. Obviously that is neglible, but we now have a run of 300' from the meter to the structure. If we were to then run the 1-1/4 to the house the friction head loss would be 11.18psi/100ft x 300' = 33.54psi. Now assuming the municipal main pressure to be approcimately 60psi the resultant pressure at the house would be 60psi - 33.54psi = 26.46psi, well below the code minimum of 45psi. Even 1-1/2" pipe would have a friction loss of 32psi and you are again under the code minimum at the house. Increasing the pipe size to 2" would yeild a friction loss of 9.66psi. Now when compared to the cost of labor to install the pipe, the pipe is actually cheap. In fact, if it were my house I would run a 2.5" pipe with a friction head loss of only 4psi. Now that we have discussed friction head loss, we have to also consider VSHL(vertical static head loss) or VSHG(vertical static head gain). To compute VSH we need to know the actual depth below grade of the municipal service water line.(Usually you can call the water suppliers engineering office, give them your street address and they can tell you) Now you have to figure out the elevation where your water line will enter your structure. If your house sits back on a hill, even though the line is two feet below grade on each end there could be a subtantial change in elevation between your house and the water main. If your house is uphill the water has to be pushed up to the house and it looses 0.434psi per vertical foot of differential, on the other hand, if your house is downhill you gain 0.434psi per foot of vertical differential. Now here is a couple tips; Check with your plumbing inspector. In most jurisdictions they will allow you to install PE or PEX line with a trencher. In fact, some trenchers have a roll pipe rack right on the machine so the pipe is laid while they are digging the trench. Although it is not required for water service, when I lay a long line such as your I like to run one strand of AWG 16 THHN wire in the trench on top of the pipe. You just leave the ends loose inside the house and in the meter box. In future if you should ever have need to locate the line a signal injector can be attached to the line and a signal tracer can be used to pinpoint the exact location of the line for the full length without any digging. Also, when they are backfilling about a foot below grade run a yellow plastic marker tape that says "Water" then finish the backfill. In future if anyone shoud happen to be digging in the area they will hit the plastic tape and warn them that they are over your water line. (you can get the marker tape at any big box home supply or plumbing supply house.

I learned my lesson and wish I went with the thicker engineered wood like I did in 2009 as it is more sturdy, feels better to walk on and is warmer. I had to redo my engineered wood floors due to damage from my water heater.