Installing Door Trim
How to Install Door Trim like a Pro
By: Mark J. Donovan
Door trim provides a finished
dressing around a door frame. Installing door Trim is easy to do, however its
best if you have access to a miter saw. For installing door trim, you will also
need a level, hammer, nail punch, measuring tape, pencil and a square. Materials
required for installing door trim include the door casement moulding, wood
filler, stain or paint, 4 and 6/8 penny finish nails and a few shims. A nail gun
is a great alternative to the hammer and nail punch as it will automatically
countersink the nails into the door trim.
Finally, if extension jambs need to
be installed a table saw or skill saw with a fence will be necessary.
Extension jambs are only necessary if you installed, for example, a door meant
for a 2”x4” wall, into a 2”x6” wall. In this situation filler pieces of wood,
known as extension jambs, would need to be installed to extend the door frame
outwards so that it is flush with the width of the door frame. If, however, you
installed the proper width door for the particular thickness of the wall,
extension jambs are not necessary when installing door trim.
If extension jambs are required, use
1”x N” “Select” quality boards. Typically I use pine for extension jambs if I
plan to paint the door trim, however if you plan to stain or apply a clear
finish to the wood door trim you may want to use a wood material such as Oak,
Maple, or Poplar for the extension jambs.
There are numerous types of door casement moulding that can be used for
installing door trim, however for the instructions in this article I used 2-1/2”
colonial casement moulding.
Door Trim Moulding
Depending upon the door you may need 3 or 6 pieces of door trim. If it is an
exterior door that you are installing door trim, you will only need 3 pieces of
trim for the interior of the door. If on the other hand you are installing door
trim on an interior door you may need 6 pieces of trim to cover both sides of
the door. For each side of the door that needs trim you will need two long
vertical members and one shorter horizontal member to go above the top of the
I typically select 8 foot lengths for the long vertical members and 4 foot
lengths for the horizontal members to give me some safety margin and for
trimming the material square.
Pre-Paint or Stain Door Trim
Before installing door trim I find it quicker to pre-paint or stain the door
trim first. This way I only need to make a few minor touch ups to the trim after
it has been installed and thus save a lot of time.
Vertical Door Trim Pieces
Using your pencil make a couple of small cross hair marks, on each side of the
door frame, on the top extension jamb and just above the left and right side
extension jambs. These crosshair marks locate the height of the inside edge of
the vertical door trim pieces. They also specify where the door trim pieces are
to be positioned on the vertical extension jambs. Please note that the crosshair
marks should be made such that there is a door jamb reveal of 1/8th to 1/4th
After making the crosshair marks, measure the distance between the floor and the
center of the right cross hair mark and make a note of it.
Next, use the miter saw to make a 45o angle cut on a piece of door trim moulding
that is at least several inches longer than the measurement you just recorded.
Note that the thicker portion of the cut door trim (in the case of colonial
casement trim) should extend beyond the thinner portion of it.
Now, measure from the inside edge (thinner section) of the door trim piece you
just cut, to the required distance as you just measured on the door frame. Use
your pencil and make a small mark on the door trim piece and then cut it at a
After cutting the door trim piece touch up the ends with paint or stain and
place it into position up against the door jamb. The lower top edge point should
be positioned up against the crosshair mark. Use the level to make sure it runs
straight and true down the length of the door jamb edge. Once properly
positioned nail it into place with 6-penny nails on the outer portion of the
door trim piece, however do not sink the nails. If the trim piece is slightly
too long, trim it accordingly before nailing it into place.
Repeat the same process for the left side of the doorframe.
Door Trim Piece
With the vertical members tacked into position it’s now time to install the top
door trim piece.
First, measure the distance between
the inner corners of the right and left vertical trim pieces and make a note of
Then make a 45o cut on one of the 4 foot lengths of door trim stock. Again, the
thicker portion of the door trim, if using colonial casement moulding, should
extend beyond the thinner portion (inner edge) of the colonial case moulding
Now measure from the inner edge of the piece of door trim you just cut, the
distance you measured between the two vertical door trim pieces. Make a small
mark on this door trim piece. This mark represents the inside edge, or corner,
of your next cut.
To make this final cut, reposition the angle of your miter saw so that you can
make another 45o cut, but in the opposite direction of the previous cut on this
horizontal door trim piece.
After making the cut, again touch up the edges with stain or paint and then
place the piece above the doorframe and between the two vertical door trim
Make sure the corners meet up perfectly. You may need to use a few small pieces
of shims behind the corners to ensure that the joints are perfectly even along
their entire seam. Also use your level to make sure the top piece is straight
and level. Once the top door trim piece has been properly positioned nail it
into place with 6 penny nails on the outside edge.
Then go back and install 4-penny nails on the inner side of all the door trim
pieces, nailing them into the edges of the door jambs. Make sure, however, not
to position the nails too near the ends of the trim pieces to avoid any
splitting of the door trim pieces.
Sink and fill the nail holes.
Finally touch up the door trim pieces with stain or paint to complete the
process of installing door trim.
For information on Installing Interior Door Trim,
Installing Interior Door Trim Ebook
from HomeAdditionPlus.com. The Installing Interior Door Trim Ebook provides
easy to understand, detailed step-by-step instructions, on how to install interior door
trim around an interior or exterior door. Pictures are included for every
key step in the process!
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