Installing a pre-hung door can be a straightforward experience when done by professionals; however, novice installers may find themselves struggling. To ensure success with their installation process, it’s crucial that their frame remains level, plumb, and flush against the drywall surface.
Use a carpenter’s level to measure and check the opening, trimming studs for plumb, and hinge side of frame at lower level than latch side; add shims under level until it centers out.
Measure the Opening
Once you have purchased a pre-hung door unit, the next step should be identifying its dimensions on your wall’s rough opening dimensions. To do this, remove any casing (or molding) around the doorway to measure.
This will expose the door studs and allow for accurate measurement. Remember to leave room for level, plumb, and square installation of your new door otherwise it won’t close correctly and may require you to slip shims between side jambs and studs for optimal operation.
Measure the Door
Once you’ve secured the door and frame in its rough opening, use a level or plumb bob to check if both wall surface and trimmer studs are level with one another. Shim the head jamb on hinge side until it meets up evenly with its respective stud.
Before taking measurements on your frame, remove any brickmould or casing that may cover it. Measure from stud to stud three times at different points across its width and use the shortest measurement as your width measurement; repeat this procedure when taking height measurements.
Measure the Jambs
Before installing your door, first verify its frame is level. Aim for an even gap of 1/8-inch between it and the wall which you will cover with casing later.
Examine the “reveal,” where the door meets the frame, to make sure that it’s even across and that its king stud is flush with the wall surface. If not, add shims under hinge and latch side jambs until they match with each wall surface exactly.
Cut the Jambs
To ensure an even reveal, use a level to check the tops of side jambs for evenness along their length and use both a level and framing square to check whether king stud and trimmer studs are plumb.
Adjust the bottom of the door frame starting about four inches up from the floor on hinge-side jamb and moving closer to strike plate until all gaps have been filled in.
Repeat for the other side of the frame. If your floor isn’t even, especially in rooms that will feature carpet, additional shims may be necessary to level it out.
Shim the Jambs
Before installing a door, make sure that its jambs are flush with the wall. Use a carpenter’s level to check that both hinge sides of the frame are level with their respective studs and latch sides are square with their strike plates; otherwise add shims underneath until your frame is level.
Maintain a 1/8 of an inch gap between the floor and bottom of the door frame to help avoid your door rubbing against it when opening and closing it. This helps avoid any unnecessary friction against it when moving it up or down.
Install the Door
An experienced contractor can typically install a prehung door within an hour. It’s much quicker than installing a slab door.
Before installing your door, apply a bead of caulk under its sill to protect it from water damage and secure its jambs to studs using screws.
Place a level on the floor at each hinge and latch side of your door frame, placing one level next to each hinge and latch side of it. If one bubble appears lower than another, simply add shims under it until its centering occurs.
Install the Hardware
Depending on the type of pre-hung door you bought, it may come equipped with trim installed or you might need to purchase and attach it yourself. If you saved the original trim piece from your old door and frame, reattaching it may also work.
To complete this project, use #8 finishing nails to attach the casing to the jambs and studs, using putty to conceal nail heads. Your finished door should open freely with perfect alignment when closing it.
Add Trim
Pre-hung doors can be heavy, so having someone help is ideal when installing them. Remove trim by prying first the side jambs then the head jamb.
Use a level to make sure the casing sits flush against the wall, and adjust hinge locations and studs as necessary if necessary. Now it is time to finish this project; with proper work completed you could install a prehung door without building a frame or mortising hinges!