How To Measure For Putting Trim Around A Window

After a window replacement, installing interior window trim puts the finishing touch on the job. If I mark the mockup of the stool here on the wall and on the other side, then I know exactly how long the stool needs to be. I can cut the casings, cut the stool, and everything will fit and come together. I could have chosen to piece the extension jamb and lower ledge together in the window opening. This house reminds me of a jack-‘-lantern with its windows appearing like holes cut out. I think the biggest difference is that you likely had to make lots of awkward angle cuts with your baseboards, these were all super easy straight cuts….I swear they were easy. The trim piece below the sill is called the apron, and it’s often made of simply a flat painted board.

I use Titebond III and find that it sets up enough in 20 minutes, enough to move the casing assy with care. Also, we’ll caulk any space between the window and the trim to make sure water doesn’t wick its way back inside and there will be an additional drip cap over the trim from that fun day I spent using the brake , but we’ll get into that when the siding fun begins.

I put up a sample piece and measure 7/8 inch to the nosing cove and make a mark on the wall. The Blinds Worksheets help you organize your window covering projects by creating a space to record window measurements, compare name brands, styles and options and to quickly view pricing, so that you can get what you need fast! Using a contrasting color, or white, on the moldings will actually make the ceiling feel lower than it is, while painting in the same color give the illusion of height. I wanted a nice, big ledge at the bottom of the window, but because I couldn’t remove the existing window sill, I had to improvise.

By designing and milling your own door and window trim, you make a style statement by controlling the size, width, wood species, and profile beyond the limited selection in home centers. I made a little mockup so that I can see exactly how this stool is going to sit in relation to the window. Draw the notch using your measurements and a pencil and cut out the notch with a jigsaw.

With an outside mount you can definitely enlarge the look of a small window by increasing the overlap around your frame or creatively dress windows that are odd sizes. If this is the case, you’ll need to use a sharp chisel and sever the stool flush with the window bottom. I carefully measured and cut the windows one at a time, and if there were two or three the same I cut the pieces all together. The rain water will roll off the drip cap onto the window sill at the bottom of the window, then roll off the window sill away from the house to the ground. Measure from the window to the wall and transfer that distance to the inner side of the stool.

Then measure to see how deep the notch needs to be. Lay this out on the stool and cut the notches with a jigsaw. Then use a straight edge to measure your window packers and bring them out flush with the tile. With the measurement marks away from the fence, it’s easy to guide the saw blade right to the mark, which you’ll see when you cut the casing legs.


You must specify the window is for a historic building even if it is for a contemporary building so you can speak to a salesperson in the right department that will understand what you are talking about. Casing a window is just like casing a door, except the casings don’t run all the way to the floor. I left 3/8 inch of the jamb extension exposed at the sides and top of the window.

The good news is that converting a window to that luxury look is very easy to do and relatively inexpensive. He holds the casing FLUSH with the inside face of jamb, scribes a pencil line along the back of the casing all the way around the opening, then beats down the drywall, coming up to the line but not crossing it. Then, when the casing slides back 1/4 in. for the reveal, all the damage is hidden.

For example, a heavy mallet helped to flatten out uneven bits where the previous owner had unsuccessfully patched and painted over lumps from (I assume) worn-out nail holes of previous window treatments. Now measure the top piece from the outside edge of one side of the MDF board to the end of the other so that your top piece will be flush with both ends of the side pieces. The windows on the left are six-over-one and the windows on the right are four-over one window designs. Remove the side casings and apply wood glue to the exposed end grain on the miters.

If you wrap the inside of the opening with 1×4 material then you’ll have enough sill for the casing to rest upon. I mainly did this because I knew that the line itself wouldn’t be straight all the way down from the top of the window to the bottom, and this gave me some wiggle room. These are small squares or rectangles of wood, often decorated with a floral pattern or a bull’s-eye, which allow you to butt the casing right up against it on both sides. Another window trim element is the cove mold, which is attached to the apron just beneath the stool, but we chose to forgo that element.

Simply measure the distance between the face of the drywall on both sides of the stool to the tip of the stools horn. Attach Top Casing to Wall: Align the top casing evenly 1/8” above the opening and nail the casing in place, leaving a 1/8” reveal between the casing and drywall opening. The size of the window opening and the window casing/trim around the window are proportional to the structure of the building they were designed to be in. Don’t destroy the architecture!

Start by measuring each side of the window from the top of the window opening to the window sill. Then reverse the angle on the saw to cut a 45-degree angle in the opposite direction. Check to make sure it’s in the right position so you have the same measurement from the tip of the horn to the jamb extension legs. As you can see, the biggest challenges that come with choosing to install your own window trim is deciphering some of the jargon. There are two methods of installing interior window trim: A) Traditional which involves installing a sill and apron, or B) Modern where the frame is picture framed involving the moulding being mitred around the entire frame.

It was actually MUCH easier than I thought it would be. I mean, I’ve stood on these things – I thought they’d be impossible to remove. If all 4 corners are within 1/8″ I will use the smallest measurement, this is so that the jamb won’t be proud of the face of the wall, when this happens the casing won’t lie flat. It should be installed 1/4-inch below the edge of the sill to provide the reveal.

You just cut away the two back corners, so the back half sits flush in the existing window sill and the front juts out in front and the sides extend just past the side pieces of trim. We decided on a trim design with a pronounced lower ledge that extended out beyond the wall with mitered casing around the top and sides and an additional piece of casing underneath the ledge to finish it off. This picture below is how the window looked, two windows placed close together sharing the same sill. I have maintained private islands in the tropics (and other places) and shoddy window installations make for tons of extra work down the line.