if you're new to carpentry have never installed wood trim before then this step-by-step video is exactly where you need to start the window we're working on today is an older existing window that previously had drywall returns which we removed in last week's video but even if you're working on a new construction window all the techniques that we're going to be covering today will work on those as well the trim we're using today is 1 by 4 primes pine which will be painted and installed with no mitered corners now if you're using stain trim or a different wood that requires mitered corners no worries I'm gonna covered miter joints in this video as well the first step is to figure out the reveals around the window the reveal is the amount of space from the edge of the window jamb to where the trim begins normally between 1/4 an inch to a half an inch I personally always use a quarter inch but this window has an existing blind that needs to go back so I'm gonna have to go with a half inch reveal to make sure that this thing fits to mark the reveals on the window you can use a small piece of half-inch wood or combination square marking the side gems and the top gem in a few different places just make sure once you get to the top upper corners your reveal lines intersect making a 90-degree angle when it comes to the bottom reveal it generally needs a larger space so that the lower sash can operate more easily so in this case we're gonna go with a 1 inch reveal now that the reveal marks are all done let's move on to the sill and extension jams the sill is the flat piece at the bottom of the window and the extension gems are the pieces of trim that extend the window jambs flush to the sheet rock let's start by finding the sill measurements the simplest way to find the silve is to take a piece of casing and lay it flat against the wall then measure from the window jamb to the face of the casing here the measurement is 3 and 5/8 from there add the amount of distance you want to sill to extend beyond the casing normally that's somewhere around 3/4 of an inch giving this cell a total depth of 4 and 3/8 to find the sill length we're going to use the half-inch reveal mark that we made on the gym and this little mock-up that I made of the extension jamb and the casing put the mock up in place and line up the extension jam side with a half inch reveal mark next make a new pencil line on the right side of the trim marking the finished position on the right side the window once that's done go ahead and make a mark on the left side of the window as well before we move on I want to make sure that you see this quarter inch reveal on the mock-up and it needs to be there if you're going to make one of these and we're going to talk about making this reveal once all the extension jams are up on the window now that both sides are marked take the measurement between those two lines and transfer that to the sill then add an inch and a half to that measurement for extending the sill beyond the casing both to the right and to the left by three quarters of an inch after cutting the sill to length and width it's time to make those sill notches now I know that's a lot of information coming at you all at once but stay with me because once we get past building the sill things going to move a lot faster and be a lot less confusing to find the knotch length locate the centerline of the window and of the sill then measure from the window center line to the right stud then center line to the left stud deducting about an eighth of an inch in each direction once you have both those measurements transfer those to the sill by measuring from the sills center line to find the knotch depth measure from the jamb to the face of the drywall on the right and on the left because sometimes those measurements are different then transfer those measurements to the sill now that we have the notched lengths and depths all marked out on the cells time to move on to check the squareness of the window to the wall to do that place the speed square against the window jamb and adjust a tee bevel so that it's tight both to the wall and to the square now if I compare the tee bevel angle to the square you can see that the wall angle is actually less than 90 degrees so if I was to make a 90 degree perfect notch in the sill the sill would fit tight against the jam and the corner but open up as it gets towards the end therefore to get the sill to fit tight everywhere always use the tee bevel angle along with your layout marks to draw the notches to install the sill line up both center lines and the one-inch reveal marks on the gym double check that the sill is actually Square to the window adjust with shims if needed and fasten with finished nails now if this feels all complete and everything is laid out it's time to move on to building the extension jams but before I show you that I just want to stop and just welcome anybody who's new to the channel and said if you want to continue to lower this please consider subscribing to the channel and leave a comment below your voice is important to me so let's move on to extension jams to get the width of the extension jams measure from the window jamb to the face of the drywall in four different areas most of the time the measurements are close enough that you can split the difference and use one number for all three pieces to get the length of the two side extension jams measure from the sill to the upper window jamb reveal and add three quarters of an inch and you'll see why in a second for the top extension jamb length simply measure from the right reveal to the left reveal once the pieces are cut assemble unit with the top extension jam between the two sides and that's why we added the three quarters of an inch glue and fasten everything was finished nails to install simply place the whole assembly in the opening lining everything up to the reveal lines and fasten with finished nails as a word of caution be careful not to let the nails push the extension jams off your reveal marks you might have to use wood shims or a pry bar behind the extensions wild nailing next go around the extension jams and mark all the quarter inch reveals like you saw on the mock-up you can do this by using a piece of wood or in this case I'm actually going to use a combination square to get the length of the side casing measure from the finished sill to the upper extension jamb reveal mark once cut to that measurement install on the reveal lines nailing into this stud with finished nails and into the extension jamb with smaller finished nails or Brad nails now if you were using mitre trim you would simply measure just as you did from the sill to the extension jamb review mark but this time that measurement would be the short end of a 45 degree miter from there you could work the top piece next measuring from the short end of the mitre on the right to the left side quarter-inch reveal mark once cut install that m
