Victorian Remodel:

Installing The Custom Traditional
Window & Door Casing

In This Article:

Traditional window sill, apron, side casings and header (or pediment) casing are installed around a window.

Related Articles:
Skill Level: 2 (Basic) Time Taken: 1 Hours

By , Editor


Earlier in this room remodeling project we tore off all the old cracked plaster and installed 3/4" rigid foam insulation with an R-value of 5.6. What an improvement in comfort! Over that we installed 1/2" Imperial Blueboard, which is basically drywall with a special coarse textured paper. On that we had a professional plasterer apply thin-coat plaster, which is about 1/8" thick.

The net result was a considerably thicker wall than before, and the sole window in this room needed to have some material added to the jambs to make them flush with the finished plaster.

The jamb extensions are just 1x4 boards ripped to about 1" wide and nailed to the original jambs with finish nails. The old jambs were sanded and the entire assembly was given a coat of oil-based primer.


 The window sill trim was installed with 2" pneumatic-driven nails. This sill had to be widened by adding a 1" strip to the back edge.

We had to be careful to make sure the sill was level. We installed a few shims underneath, by opening the window and slipping them under the board.


 The trim under the sill, (which we call the apron), went on next. We held it in place with two Quick-Grip clamps.


We used the air nailer to nail through the sill into the apron.

But our 2" nails would not even reach the framing when driven through the face of the apron.

We normally use 2" or 1-1/2" nails to attach trim, but in this room our longest air nails would not reach the studs. Consider the thicknesses of our materials:

Trim - 7/8"
Plaster - 1/8"
Blueboard - 1/2"
Foam Insulation - 3/4"
Wood lath - 3/8"
Penetration into stud - 1"
Total nail length needed: 3-5/8"

Our 2" pneumatic nails would only reach into the foam. The longest air-driven finish nails we have seen are 2-1/2", which would not work here.

So we used 3-1/2" 16 penny hand-driven finish nails. We pre-drilled each hole to prevent splitting of the trim.

This completed the installation of the sill and apron.

 The next step was to install the side (vertical) casings. We marked the edge of the jamb to leave a 1/4" reveal.

The tool used here is an adjustable try-square, a very handy device and well worth the 8 bucks spent. We just hold the pencil against the end of the ruler and slide the square along the edge.


 We had to remove some of the plaster and blueboard at the lower part of one side. We cut a line to control how the wallboard would peel, and used a chisel to remove a thin layer of plaster.


 We drilled holes in the side casing and nailed it in place. We used a 2' level to make sure that the vertical pieces were close to plumb.

Often when installing casing there is a trade off between plumbness and consistent amount reveal.


 The next step was to pre-drill some holes in the top section. There was a big 2x6 header above the window and ample solid wood to nail into.

We set the top in place...


 And drove in some big finish nails.


After everything was nailed in place we used siliconized acrylic latex caulk to fill in the gaps and nail holes. This caulk shrinks very little.

After installation we touched-up the paint.

We normally pre-prime and pre-paint all of our trim before installation. Afterward there are nail holes and gaps to fill, which then must be touched up with paint.

Some people might view our method as too time-consuming, but there are several advantages to our approach:

1. No need to mask around the trim. The areas to touch up are often small and always well away from the edges of the board.
2. Painting takes place in a clean shop, with the boards lying flat on saw horses, so the paint does not run, drip or get dust in it.
3. After the paint touch-up, the face of our trim usually has two good coats of paint.
 This top section of casing looks so much better than the original... and it's consistent with the style found elsewhere in the house.



Tools Used:

  • 2 Foot Level
  • Torpedo Level
  • Cordless Drill
  • Hammer, Nail Set
  • Pneumatic Finish Nailer
  • Assorted Hand Tools

Materials Used:

  • Particle Board
  • Colonial Baseboard
  • Colonial Door Stop Trim
  • Bed Molding (Small Crown)
  • Decorative Trim
  • Wood Filler


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Copyright 1999, 2005

Written August 2, 1999
Revised January 10, 2005