The bathroom forum will be your best resource.

There are code requirements for slope to a drain as well as the height difference between the drain and the floor. Drain placement will depend on where you contractor CAN place it, as well as where it "fits" to get the proper slope to every part of your shower pan.

Linear is not necessarily any better than regular drain. They all go through the floor eventually. What linear does do for you is get a planar slope (on the whole floor) instead of a "conical" type slope. However, I am not convinced that linear is "better" than regular single point drain.

We have a zero entry shower. It has a regular round drain. We have no problems with it draining properly.

HOWVER, when your contractor says he will "lower the floor via the floor joists", if you have i-beam joists make ABSOLUTELY certain that he is not thinking he can cut down into the top edge (flange) if the i-beam joists. The flanges of i-beam joists CAN NOT be cut. If the flanges are cut or knotched, the joist loses structural integrity. Do NOT let him cut or knotch the flanges...even if you have to give up on the idea of a curbless shower entirely.

Before we fired him, cutting the top flange of the floor joists running under our second floor master shower was just one of the many mistakes our sorry-a22ed builder made! He had previously ignored our architect's carefully designed joist specifications. If he had followed the specs, the master shower area (and our laundry room) would have been framed with their floors about 4 inches lower than the rest of the second floor. Instead he figured it would be cheaper to run longer joists and then just "cut the floor down" in those two areas.

It cost us a minor mint to get that mistake fixed so that we didn't have to worry about the joists caving in! And we were only able to fix the mistake - and still have a roll-in shower - because the shower had been positioned so that it was sitting squarely over two walls downstairs that could be used as additional support walls for the i-beams the builder had cut plus some new, shorter joists that had to be run under the shower floor. (The guy who installed the new joists had to do acrobatics to retrofit them in.)

Fortunately I stopped our builder BEFORE he cut the the flanges on the i-beam in our laundry room. There we solved the floor drain problem by building a raised section with a sloped floor for the washer and dryer to sit on...basically a raised "shower floor."

If you wanted a curbless shower at the start, your architect should have specified in detail how the floor framing should be done so that no i-joists would need to be cut. If your curb-less shower is a "change order," please do yourself a favor and hire an engineer to design exactly how the change can be made without sacrificing the integrity of your floor joist system.

If your floor joists are SOLID wood, maybe they can be cut down enough to accommodate the curbless shower. I don't know. Since our builder used i-beams throughout, I didn't wind up having to educate myself on what is allowed when cutting into and knotching solid wood joists. I'd still strongly recommend you get an engineer's opinion before allowing him to cut down the joists. It might cost you a couple of hundred bucks but better to be safe than sorry.

Our curbless shower is large enough that we don't have a door on it so I can't respond to the question about the door going over the carpet.

My contractor also had to lower our floor for a zero entry shower. He had to cut the joists, but then he installed something else? Whatever he did, he ran it by our engineer during inspection before proceeding. Our joists are still exposed so I can take photos if anyone would like.

I do remember our GC saying that we could not just cut the I-beam joists.

We decided on a curbless shower after the framing process, so it was not accounted for in our original construction drawings.

Are you really convinced you must have a flush floor shower? Is there someone in your household who has difficulty with a normal "curb shower"?

You are embarking on a very complex design and construction effort to simply have a "flush" floor. The descriptions above help illustrate what is involved.

Is it worth it?

"How silly!", I thought bevangel was in warning about not cutting wood I-beams. Only an idiot would do that! Then I finished the post.

You can notch dimensional joists (2x10s etc), but only within Code limits. Anything more and the structure has to be reinforced with additional joists or headers.