Installing trim on a stair railing can improve the look and finish the area. It’s something that takes some thought. The trim itself isn’t on the handrail, whose aim is to provide support as you go up and downstairs. Instead, the trim is over the horizontal area and down the vertical area, on top of the drywall. Using wood for this can help it blend in with other woodwork and give a final touch.
Step 1 - Design
Start by deciding exactly where you want to place the trim on the stair railing. Generally, this will be on a relatively small surface on the top of the stair wall. You’ll also need to go down the vertical on the edge of the wall at the bottom of the stairs, and also on the riser up to the ceiling at the top of the wall.
Step 2 - Measure
Measure the length of the top of the stair wall and make a note of this. You also need to measure the height of the riser and the stair wall. Use a square or protractor to judge the angle where the wall meets the riser and where the top of the wall meets the vertical at the bottom.
Step 3 - Pick Wood
Choose suitable wood for your trim. If there is other trim in the house, try to match that. If you can’t, you can stain it to match. Be sure that the wood you buy is straight, as you don’t need to fight warps. Purchasing high-quality wood will help ensure this, but check every piece before you buy. Your trim should be 1 inch thick and ½ inch wider on each side than the wall.
Step 4 - Cut
You need to cut the wood to size. Start with the longest piece, which will be along the stair wall. Cut the width first, using a table saw. For the length, make it 1 inch longer than the wall to begin.
Your first cut should be the miter for the top of the wall where it meets the riser. Set the wood sideways in the miter box and cut. Now fit the wood into place and mark where the wall ends. You’ll make your other miter cut here for where the wood will meet the vertical trim. Repeat this for the vertical. For the bottom, the cut needs to be square. Make that cut and then the miter cut at the other end. Finish by cutting the riser. The top will be square with the wall and the bottom cut to the miter so it joins with the longest part of the trim.
Step 5 - Install
Dry fit all the pieces together first to check that your angles and measurements have been correct. Use finish nails to put the riser in first, then fit the long piece, and finish with the vertical. Countersink the nails and cover with a little wood putty, also using it on the miters if they’re not exact. Give it time to dry and then sand the wood all over with fine-grit sandpaper. To complete, stain if needed and then apply a coat or polyurethane finish to protect the trim.