Temp support wall from ceiling to floor.
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@franklin2 is on track here, except that red wall should go a couple of joists past whatever you’re going to take out on each side.
The temp wall should have a double plate on top with offset steams at least two studs apart. If you do 16 inches on center on the studs, that’s best, and you can probably get away with 24 inches.
Measure the space between the white ceiling in the floor, and build your wall on the floor quarter inch taller. Put it in place at the top with a couple nails, and then drive the bottom so it goes vertical with a sledgehammer. Do you want to pre-loaded, you don’t want to settle when you pull the wall out.
you need to be sure if you put it under that white ceiling, that the white ceiling will hold a load, and you don’t just crush the white ceiling.
@2drxploder is right that the cleanout can be cut really anywhere you want it. If you’re going to pour a concrete apron up to the door, I would make it a hair lower than the concrete so that there is no pressure on the pipe if you drive over it. Also, the cap on it now opens with that square knob sticking up. They make a cab that has a recessed square that you open with a half inch socket or such, so it’s flush with the surface.
Also, keep in mind that the drain pipe is vented and it drains. If a little rain water gets in, or a little vapor gets out while you’re figuring it out, it’s not the end of the world. So the cap really doesn’t have to be airtight. If you have any doubt about the height you want, just leave it a little bit long and put the female adapter on without glue. Then when you figure out where you want it, you can just pull the female adapter off, cut the pipe, and then put it where you want it.
And you seem sold on the sliding door, and if that’s what you want, God bless you. If you have the slightest doubt, call around some of the overhead door people and the steel door people, the commercial suppliers not Home Depot, and see if they got any scratch and dent or used that they will sell cheap. If it was my front door in my house I wouldn’t do that, but if I’m working on the back door of my shop which faces in AlAnd you seem sold on the sliding door, and if that’s what you want, God bless you. If you have the slightest doubt, call around some of the overhead door people and the steel door people, the commercial suppliers not Home Depot, and see if they got any scratch and dent or used that they will sell cheap. If it was my front door in my house I wouldn’t do that, but if I’m working on the back door of my shop which faces an alley....