Regarding plumbing,?

Is there a standard height from the floor for the water lines that come out of the wall for a bathroom sink and toilet? I know it's a good idea to run them through a peice of 2x4 or 6 before putting up the drywall. I also know about the extension inside the wall with a cap on the end to absorb shock when the water is turned off. Oddly enough no one in the plumbing dept. at Lowe's or home depot seems to know the answer to this.