[LazyPup]

Based upon the information in the original description you have a couple far more serious problems than just the vertical height.

Quote; "The pipe coming out of the wall is 1 1/4" chrome and is cemented into a Tee".

First of all, the chrome plated pipe is not pipe at all, but rather it is chrome plated brass tubing, and code strictly prohibits installing it in a concealed location.

Second, the post says that the chrome pipe is cemented into a Tee on the 1-1/2" galvanized vertical combined waste & vent stack. Not only is a cemented joint prohibited, it is almost a certainty that it will leak in a very short time. The proper method of joining the plated tubing to pipe is by means of an approved Trap Adapter and the transition joint from tubing to pipe may not be in a concealed location.

The drywall is the least of the problems, and one that can be handled very easily. Begin by placing a mark on the drywall at the desired height for the new fixture arm, then measure up about 10" and using a level, make a horizontal line long enough that it will reach from stud to stud. Next measure down from the fixture arm and make another horizontal line as before. Now use a hand sheet rock stab saw and carefully cut along the horizontal lines until you can feel the stud on each end of the cut. (Caution here, be sure to use a hand saw because you will be able to feel if the saw hits a pipe or electrical cable in the stud bay.) Once you have the two horizontal lines cut to the studs, you can then begin at the top and cut downwards parallel to the stud and carefully pull the sheet rock out. Set the piece of sheet rock aside because it is the exact size to go back in, leaving only a simple tape joint on all four sides. Now measure the vertical length of your opening and cut two pieces of 2x4 about 3" longer. You can slip one of the 2x4 pieces in the opening on either side with the tips of the 2x4 behind the sheet rock on the wall and sister them in along side the stud. After you complete the plumbing work you can slip the sheet rock back into the opening and secure it with sheet rock screws into the cripples on either side. (hint, sometimes it is difficult to get 2x4;s in the cavity. I like to use 2x3 then after it is slipped into the opening with the tips behind the sheet rock on the wall, pull it forward tightly before screwing it to the studs. The key is that the front face of the cripple must be tight against the existing sheet rock on the wall at both top and bottom to insure the piece of sheet rock you use to close the hole will be at the same level as the wall, leaving a nice flush line that can easily be mudded and taped. I often use lightweight spackling to mud the joint so that you can be ready to paint it in an hour)

Once you have the opening made you can cut the vertical pipe as described above, however, a word of caution here. Galvanized iron pipe is quite heavy. Before you cut a section out, make sure the remaining pipe above the cut is securely fastened to insure it will not fall when you cut the piece out. In some instances the vertical vent line behind a lavatory will have a horizontal offset just above the lavatory. If so, it will be self supporting, but if that line runs straight up to the roof I would not trust the existing hangers. In this case i would go into the attic space and locate where the line comes through the attic floor, then attach a pipe hanger on the pipe, so that the underside of the hanger is resting tight against the floor or a framing member to prevent the pipe from dropping down. This may seem like a waste of time, but I can assure you from personal experience that the time lost securing that pipe will not be nearly as much time as you will lose repairing the damage if the pipe falls down.

The code standard for a lavatory drain line is 1-1/4" however code allows us to increase the size of a trap or drain line by one nominal trade side, which would then be 1=1/2'. Understanding that the lavatory is the only drain in a residential structure that is allowed to be 1-1/4" most plumbers prefer to install and 1-1/2" fixture arm rather than maintain a separate inventory of 1-1/4" pipe and fittings for this limited use. As a consequence it is nearly impossible to find 1-1/4' pipe and fittings in most home supply centers or hardware stores. For simplicity, i would suggest you install an 1-1/2" sanitary Tee, with a short stub 1-1/2" stub out and install an 1-1/2 trap adapter where the pipe exits the wall. Inside the trap adapter there is a plastic ferrule that makes the water tight seal. If you want to continue using the 1-1/4" trap they make an 1-1/2" x 1-1/4" adapter ferrule that fits in the trap adapter. (Many trap adapters come with both the 1-1/2" and the 1-1/2x1-1/4" ferrules).

A word of caution when selecting your Tee. Be sure you get a DWV grade (Sanitary Tee). A pressure Tee, Wye & 1/8th bend or a combo is prohibited here.