When it comes time to change out or install an opening in a wall, like a door or a window, there are certain considerations that should be taken from the beginning. It’s a good idea to have measurements from or have the door / window and frame already purchased, so you can rely on those measurements while doing any work.
First, if this is part of any new construction project, the framework will already be exposed for easy modification of the studs. This is the easiest point in which to cut and install any opening for a passage, door, window etc.
Secondly, when the walls are finished, (drywall, plaster, exterior materials, etc.) there’s more work to be done, let alone the decision of where you would like the opening to be. Keep in mind you may have to move any plumbing or electrical if it is in your desired location of work.
We will be discussing the installation of a pre-hung door . This is a door package, like a kit, and it makes the whole install process go much easier and faster. These ‘Kits’ are sold for a variety of installs. Whether it be a glass sliding door, or a high end front entrance, with side windows and such.
When starting this project with finished walls, you will need to determine where the framework is inside the wall and cut into the wall to create an opening from top to bottom, left to right, slightly larger than what you desire. Usually by one studs span (roughly 14 1/2″ – 16″) and then replace the stud at the correct spot to receive the frame of the door. Keep in mind that working with drywall from the inside is easier and cheaper to open up the walls, than ripping into to exterior surfaces.
For strength, the opening (any opening) will need a header, which is a beam above, usually a 4×4, 4×6, or larger, set with king studs and trimmer (jack) studs. King studs run the complete height from bottom plate to top plate. Cut these snug, not loose, and tap them into place. You should see this if you opened up the wall correctly. Then the trimmer or jack 2×4′s are the movable studs that set the door or window correctly with shims. The header sits just above the trimmer or jack 2×4′s, nailed to the king studs. Cripple walls may be needed above the header, if the header does not reach the top plate. At this point you will need to rely on the measurements from the door and frame or window that you are installing. Note: The header length should be slightly longer than the width of the door frame or window.
Once you have the framework ready for the door frame, install the frame and door or window into the opening and plumb / level. Always start at the hinge side for a door, and mount the door frame to the jack/trimmer studs using shims if necessary. These particular studs are movable sideways to close up large gaps in the framework. Shims are used to fine tune the plumb-ness of the opening.
Note: If this is not done right, the door may close or open slowly on its own.
Once all the fastening is completed, test the door for latching, squareness. Replace or add drywall to the framework, and mud (drywall compound) the work to match the existing wall. Add the door casing (molding) around both sides of the frame to give it that finished look. Now all you should have left is to prime and paint.