- 1). Measure from one corner out along one wall. Mark out the measurement on a piece of trim moulding.
- 2). Set the trim moulding on your miter saw in the position it will go on the wall, standing on its bottom edge with the back of the trim against the fence of the saw. Set the mark from the corner so it's under the blade.
- 3). Turn the blade to 45 degrees, pointing toward the main part of the trim. Cut the trim. Slide it to the other mark, turn the saw blade in the other direction (so it again is pointing toward the main span of the trim) and make the cut.
- 4). Repeat the process for the second piece of trim that's coming off the same corner, on the other side.
- 5). Hold the two pieces of trim moulding to the wall where they will go with their miter cuts butting against each other in the corner. Use a trim nailer to install them, shooting the nails along the top and bottom edges of each piece, about a foot apart. Repeat the whole process for each wall.