Door jambs are the vertical portions of a door frame on both the hinge and strike side of the door.
The door jambs are used to mount the door frame to the wall.
Most door jambs in homes are made from wood, and after the door trim is installed, most of the jamb surfaces are no longer visible.
In most cases the existing door jambs are of the proper thickness to match the depth of the wall that surrounds the door, but sometimes there is a discrepancy, with the wall coming out further than the door jamb.
In situations like these, extension jambs are used to bring the jamb out to the proper thickness to match that of the wall.
Measuring and Cutting the Extension Jambs The depth of the extension jambs needs to be the difference between the depth of the existing door jam and the outside face of the wall surrounding the door.
Measure carefully, because the depth might vary slightly between the two sides of the existing door jamb.
The extensions can be cut from strips of lumber, or from a spare door jamb.
For door trim that will be painted, pine is fine to use for extension jambs, but when using a stain or clear finish, woods such as maple, poplar or oak to match the door trim would be the best choice.
The extensions will be cut to the same width as the measurement between the existing jambs and the wall surface.
A piece will also need to be cut to extend the top head piece.
Safety Precautions Safety is always important when working with tools.
Be sure to wear safety goggles, and remember that doors can be heavy and difficult to manipulate, so get some help if necessary.
Installing the Extension Jambs The door will be installed even with one side of the wall, and on the other side you will install the extension jambs to bring the existing jambs out level with the wall.
The extension jambs are installed on the side of the door frame that is opposite the hinges of the door, to prevent problems when opening the door.
To attach the extension jambs, use staples or finish nails, measuring to make sure the extensions bring the jamb depth out even with the existing wall surface.
Start by installing the top piece first.
When held in place, it should fit up against the existing top head piece, with the outer edge flush with the wall.
When you are sure it is a good fit, it can be nailed in place.
Do not sink the nails, as adjustments might be necessary.
Repeat with the vertical pieces of the jamb extension.
If there are any uneven areas, shims can be used to adjust the extension jambs.
Once all pieces are in place, measure and check with a level to make sure everything is square and level.
Then, sink the nails, fill the nail holes, paint or finish, and proceed with installing the door trim.