During the installation of your carpeting, you may have exposed edges, such as at doorways or on staircases. In these cases, you need a way to conceal the exposed edges so that your carpet does not fray and looks professionally finished. Folding the carpet edges under is one solution to this situation. Because carpeting is so thick, you will have to prepare the carpet by scoring it before you fold it. Like all carpet installation procedures, this is heavy-duty work, but it is a relatively straightforward process.
Measure the area where you want to install the carpet. Add 2 ½ inches to both the width and length dimensions to allow for the folded edges.
Trim the carpet with a carpet knife so that the edges are perfectly straight. Remove any strings or ravels.
Turn the carpet facedown and place a metal straight edge along the edge of the carpet to be folded; leave 1¼ inches of the carpet showing between the straight edge and the edge of the carpet.
Hold the straight edge firmly in place. If the straight edge is wide and long enough, kneel on it with one knee to hold it down.
Score the bottom of the carpet with an awl along the straight edge. The idea is to weaken the bottom binding. Do not cut through the bottom; you only want to create a straight line that is easily folded.
Turn the carpet over and put it in place.
Fold the scored edges under before you tack the carpet down.
Install the folded carpet edges with carpet tacks every inch or so to prevent lifting. If you are using carpet padding, cut the padding 1¼ inch short of the edge so that it does not extend under the folded carpet edges. This keeps the carpet flat along the edges. Consider using self-adhesive carpet binding instead of folding under the edges for a flatter finishing technique.
Use caution with sharp carpet knives. Wear heavy-duty work gloves to protect your hands.