Installing a shower stall can be a pretty tough assignment, especially if it's a one-piece unit. This can be exacerbated if you have to contend with stairs. A better choice would be a 5-piece shower stall that can be carried one piece at a time and assembled in the bathroom.
Step 1: Determine the Right Size Shower Stall
First you need to determine how large a shower unit you can accommodate. Measure across the back wall and mark the exact middle. Start at the top of the area and draw a straight line down the length of the wall. Use a level and plumb line to keep the lines straight. Carry the line across the bottom to the very edge of the enclosure. Next, starting at one side of the shower area, measure around the entire area until you reach the other side. This is the measurement you need to choose your shower stall.
Step 2: Size Panels
After you receive your 5-piece shower stall, begin installation by taping the back corner panels in place. Measure them to fit to size and make sure that they will fit. Use a jigsaw and cut them to size. Mark the location of the control valve handles and the shower head on the panels. Measure up from the bottom of the shower floor, and from each side. Transfer these to the panels and cut out using a hole saw attached to a drill.
Step 3: Dry Fit Panels
Once the appropriate cuts have been made, install the panels with tape to check the fit. Insert the shower bottom in place. Then put the corner panels in and set the back and side panels so they overlap. Once you have them situated the way you want them, mark their locations in relation to each other near the top of each panel. This way, when you permanently affix them, they will be exactly where you want them.
Step 4: Permanent Installation
Remove all the pieces and begin with the corner panels. Place a line of caulking on the back of the panels in a zig-zag pattern. Press firmly into place making sure it is straight. Follow this up with the other corner panel. Clean the corner panels, and the remaining panels with mineral spirits to get rid of any oils, and dirt, that will interfere with the adhesive. Once they are all dry, install the remaining panels in place.
Step 5: Clean off Shower Stall
Once everything is set into place, wipe off any excess adhesive with a clean rag and mineral spirits. Install the control handles and the shower head. Apply a bead of caulking around the seams and flatten out with a putty knife.