Jamb moulding components are available and DIY installation is a lot easier if you apply a few clever tricks to speed up the job.
If the walls are out of plumb or the floors aren’t level, you will need to correct these problems first or the door won’t open and shut properly.
Once the jamb is secured in position, you may need to trim the door to size before cutting housings for the hinges and hanging the door.
Use a drill with a holesaw and spade bit to bore the holes for the lockset and latch, then finish by securing the architraves.
Pack the jamb
Instead of standing the doorjamb in position while you insert wedges behind the hinge side, secure shims in the door opening first.
Measure the width of the doorway opening to calculate the thickness of the shims you will need.
Usually the opening allows for a gap of about 10mm on each side of the doorjamb.
If the opening is extra wide, you can use smaller wedges by temporarily securing offcuts of 12mm plywood at each of the hinge locations, then adding wedges or shims to plumb the jamb.
Position the shims at the top and base hinge locations using a long spirit level, or a straightedge with a shorter level, then add the centre shims if a third hinge is needed.
Allow for flooring
New flooring always looks best if it fits neatly under the doorjamb, otherwise you’ll have to cut around the intricate shapes of both the stiles and the architraves.
Save yourself time and trouble by cutting off the base of the jamb before the flooring is installed.
Measure the thickness of the floor covering and calculate how long the stiles will need to be to clear it.
If practical, use an offcut of the actual flooring as a spacer under each stile as you install it.
Plumb the opening
Doorway openings in stud walls that are out of plumb can make door installation problematic.
As long as the base of the wall isn’t locked in by flooring, the solution is simply to nudge the base plates on both sides of the opening back to plumb.
You will need to cut the nails securing the base plates using a reciprocating saw or oscillating tool, then move the walls into position using a sledgehammer.
Check for plumb and if either side is more than about 7mm out of plumb, adjust the wall before you install the door.
TIP: Once the walls are plumb, reattach the base plates to the joists by skew-screwing in place.