How much green board or cement board for shower

I am remodeling my shower and when I pulled the tile down I took down one layer of green board with it. There was a second layer under that attached to the studs. While doing research I noticed that some pics have 1 layer of green board and some have 2. Is there any code that guides the number of layers or is 2 just generally better? Can I get by with just one? Should I replace the green board with cement board?

Thanks, Jeff

Greenboard is only waterproof until you put a nail or screw in it...forget about it in a shower. Use cement board. If you want, you can use plain drywall if you use a product called Kerdi. www.schluter.com makes the stuff. It is a waterproofing membrane.

Thanks, how many layers do I need, 1 or 2.

Typically, you'd only use one layer. Based on the pan size, they may have used two to get it in the right position. Structurally, you only need one layer, to get the walls in the right place, unless you are replacing/rebuilding the entire thing, you may need to duplicate the existing thickness. You could do that with shims and one layer, or two. Cement board on the ceiling can be a problem - check with the manufacturer to determine the maximum span, especially if you are going to put thick, heavy tile on it. You may need to put up some cross bracing to minimize the maximum span. Greenboard on a ceiling should be supported every 12". You could put up fire-rated 5/8" drywall which is stronger and tile that (unless it is a steam shower).

Great, just what I was looking for. I'm not doing the ceiling, just the surround. I think they did use the extra wall board for spacing on the surround.

My new pan needs a rough in of 36" and my studs are 36.5 so I should be okay with the wall board taking up the rest, i hope.

You've got the idea. It all depends on the rough. You want the board to overlap the flange of the pan, but not all the way to the deck. Keep it up about a quarter inch to prevent wicking. Now, you also do not want the board to be "kicked out" at the bottom. This is where the thickness comes into play. I like to furr out the studs with 1/4" lath strips. This usually will allow the board to be plumb over its entire height.

Greenboard is definitely old school. It just is not good enough. Must use cement board.

Thanks, I want to use cement board, but they had 2 layers of greenboard up and I only ripped out the first layer, it came off with the tile. The second layer of greenboard is still in perfect shape so I think I will leave it.