Fine Tune Your Door Installation
The first step in door installation is to measure the rough opening
to see if the prehung door will fit in the opening. The rough opening
for a door unit should be at least 2-1/4" wider than the width and the
height the door. For a 36" wide x 80" high door, the rough opening
should be at about 38-1/4" wide by 82-1/4". Anything less would be
asking for a tight fit between the framework and any thing more would be
asking for a loose fit. Meaning one would have to add shim strips
to the frame to have a comfortable fit for the wedge shims to work.
However, always check the door specifications for proper rough opening
size. For a door jamb which is 3/4" board thickness and 1/2" spacing
between floor and bottom of door, a two inch rule of thumb is added to
the overall door measurements to obtain a rough opening size. Let's
see how the rough opening measurement is calculated.
Door width = 36"
Door Jamb Thickness = 3/4" + 3/4" = 1-1/2"
Spacing between door and door jamb = 3/32" + 3/32" = 3/16"
Total width = 36" + 1-1/2" + 3/16" = 37-3/16"
Door Height = 80"
Door spacing between bottom of door and floor = 1"
Door spacing between top of door and header jamb = 3/32"
Head jamb thickness = 3/4"
Total height = 81-7/8 "
To continue the installation process, the floor is checked for level. Since the side door jambs rest on either side of the rough opening, it is desirable to have a level floor. If the floor slopes to the left or to the right and depending on much a slope there is, a full wedge shim may have to be cut and fastened onto the floor to compensate for the elevation difference. This will also help stabilize the sill of the door frame. However, if a prehung door without a sill is used, the lower end of hinge side of door jamb will have to be raised or lowered or cut so that the top header jamb will be parallel with the door. (Note - By lifting or cutting a jamb will adversely affect the opposite door jamb. Either way, if one side of the jamb is raised, the other jamb will have to be lowered or cut to match the difference in elevation.)
For a prehung door with a sill and brick mould finish, the frame is inserted into the rough opening and the brick mould side is pushed tight against the wall frame as one checks for a even fit all around the perimeter
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