Adding Trim to Stain-Grade Wood Windows
After cutting out the stool ears with a jigsaw, check it in location to be sure it fits against the window frame or jamb extensions all the way across and fits the wall surface. Adjust as needed.
Preassembling the stool with the other three surround boards makes a box that can be installed in one piece.
When setting the window surround, ensure that you have consistent reveals, using shims and a straight edge to make sure everything stays in place and is even.
Measure the window stool to determine the length of the apron, which should account for the reveal to the casing as well.
After double-checking the reveal at both ends, nail the apron in place snug beneath the window stool.
The vertical casing boards can now be cut to length at the reveal mark on the horizontal surround board. Before nailing, check that the casing touches the surround all the way up and is fairly flat on the wall surface. Adjust as needed and nail into place.
The parting bead is determined by the measurement from one side of the casing to the other, plus the reveals. It will usually be the same length as the window stool.
Here Taylor leaves the parting bead a little wide and marks for scribing so it fits tightly against the window surround and against the wall surface.
Keeping in mind what will be visible after installing the header helps in the notching and scribing process. In this case, the surround protruded a little so the extra material is above the casing. Sometimes it’s the other way around, and it takes more material in the inside part to reach the surround.
Fastening the parting bead to the casing will hold it in place while you install the header.
After cutting the header and nailing it in place, a small finish nailer can be used to fasten the parting bead to the head casing.