The first step in constructing a window frame opening in your new wall is to lay the top plate and bottom sole plate side by side on your workbench or saw horses. Use a framers pencil to mark the location of the wall studs which are the vertical 2×4’s or 2×6’s depending on the framing design of the home. For discussion purposes in this article let’s assume all measurements are from the left end of the wall plates.
Typically, the wall studs are on 16 inch centers so starting at one end place a mark every 16 inches. Then using a small framing square, draw a line across both the top plate and the bottom plate, placing an “X” adjacent to the line on the right-hand side of the line. The “X” designates the location of the vertical studs.
Determining the Rough Window Frame Opening Dimensions
To determine the rough window opening, measure the outside dimensions of your window assembly. Allow and extra ½” all around the window. For a window with overall dimensions of 48”, use 49” for the window opening.
Do the same for the door opening. Measure the door jamb assembly. If it is 36” wide allow ½” to the left and right so the gap should be 37” wide. Measure the height from bottom of sill to top and add ½”. So, if the assembly height is 81-1/2” the opening should be 82” high. For the windows, you will leave the bottom sole plate in place. For the doors, in most cases you will remove the bottom sole plate after the wall is standing and secured.
Mark the Window Location
Mark the horizontal location of the window measuring from the end of the bottom plate to the beginning of the window opening. You can find this dimension on the wall plans. Place a “TR” on the left-hand side of this mark to designate the location of the first window opening stud, known as a “Trimmer.”
Mark the location of the “Cripple” which is a short stud beneath the window sill. In this case draw a circle around your “X” to differentiate it from the regular studs.
Next you need to locate the trimmer on the opposite side of the window frame opening. So, if the first trimmer mark was at 24” and your window is 48” wide you need to add 24” plus 48” plus the ½” allowance on each side, so this mark will be at 73”. To identify the location of this trimmer, place a “TR” on the right side of the mark and a cripple mark (circled “X”) to the left of the line.
Now you need to go back and circle any “X’s” that fall between the “Trimmers” as all of these will now become “Cripple Studs” as well.
Now is a good time to pre-cut your components. You will likely have a stockpile of 2×4’s that are 8-foot-long from which you will cut the various components. In the case of the vertical studs, rather than cutting each 2×4 to length you can purchase pre-cut studs from your hardware store. These are generally 92-5/8”, which are perfect for a wall with a double top plate, and will save you a ton of time.
When cutting your cripple studs, remember that a 2×4 is actually 1-1/2” x 3-1/2”. To determine the cut length, subtract 3” from the desired height of the underside of the new window sill. So, it the underside of the sill is 24” cut your cripple studs at 21” long. To determine the length of the trimmers, add the height of the window opening. So, for our 48” window we add 48” (window overall height) plus 1” (for clearance) plus 24” (the height of underside of the sill) minus 1-1/2” for the bottom sole plate. The net in our example is 71-1/2” overall.
Before you fabricate the header, you need to confirm the requirements per your local code. The most common size for a header with a span of 48” is a pair of 2×6’s. Check out our article on how to build a header to see the most common header dimensions. In our case, to construct the header you will need (2) 2×6’s, (1) ½” x 6” filler strip, and (1) 2×4, all cut to a length of 49”. To meet code, you need rows of 3 nails every 12 to 16 inches. Nail the pieces together on both sides.
Pre-Fit the Components
Before you start nailing everything together it’s a good idea to lay all of the components on the floor to confirm that all your dimensions work out okay. The most important dimension to check is the window frame opening itself. In our example, for a window with exterior dimensions of 48” x 48” we should have a clear opening of 49” x 49” between the 2×4’s.
Once you have confirmed the overall dimensions of your wall including a triple check of the window opening you can nail the structure together. Use 2 nails per connection. With respect to the cripple studs, and the trimmers, they should be nailed together with a pair of nails every 16 inches.
Check for Square
Before you add any sheathing make sure the assembly is square. Measure corner to corner over the entire wall section. The two dimensions should be equal. Do the same for the window frame opening itself to ensure it is square as well, otherwise you will struggle immensely when it comes time to install the window assembly into the window frame opening.