Restoration Guide: Windows and Doors Casing

Barbara Marquand

Editor's Note: This is article 8 of 12 in Chapter 4: The Windows and Doors Guide of Old House Web Restoration Guide. This guide was developed and edited for old homes from original materials in the U.S. Housing and Urban Development Rehab Guide.


Casing--the trim for windows and doors--covers the gap between the rough opening and the window frame or door jamb. Besides providing a finished look, decorative casing gives windows and doors their character and impacts the overall style of your old house.

Section 1--The Essentials

Traditionally you needed several trim parts to install a window or door--sill and drip caps for guiding water away from the opening, head and side casing or aprons to cover construction gaps, and stools or jamb extensions that covered the width of the frame. Now manufacturers typically include casing as part of the unit, or they offer pre-assembled casing and jamb extension options.

You can repair wood trim using similar methods to those discussed in the window frames section. For replacement projects, you're not limited to solid wood. A variety of new engineered products are designed to look like traditional wood trim but are less expensive, require less maintenance, and are free from imperfections. Thanks to the consistency of many of today's newest trim products, you can achieve the look of fine craftsmanship with limited carpentry skills.

Engineered wood products include:

  • Finger-jointed stock, which is made of many short pieces of solid woods glued together
  • Laminated veneer lumber, which features multiple layers of thin wood glued together, similar to plywood
  • Hardboard, made from highly compressed wood fiber
  • Fiber cement, which is made of sand, cement, and wood fiber. Although it looks like wood, it's fire, water, and insect resistant

All are available in up to 24-foot lengths and are a fraction of the cost of premium solid wood.

Factory-finished casing provides a long-lasting, consistent finish and cuts down on your labor time or costs. Corner trim now comes pre-assembled and butt jointed, for instance, and some new materials use adhesives or interlocking screws to weld parts together.

Section 2--Repair and Replacement Considerations

2.1: Repairing Wood Trim

Determine what caused the trim to deteriorate and then correct the problem before you start any preservation work. You can repair or replicate almost any trim with new epoxy and consolidant products, but it will take some elbow grease, and the effort might not be worth it unless the damage is very limited or historic preservation is a top priority.

In deciding whether to repair trim, consider the condition of the existing trim, availability of matching trim, and the potential for contamination from lead-based paints. You'll need to remove damaged portions before applying the epoxy or consolidant, and if you don't apply it correctly, the filler might come loose later because of improper bonding.

2.2: Installing Solid or Engineered Wood Trim

You can modify solid or engineered wood trim easily to fit your installation project. Consider pre-finished solid wood or veneer-wood applied trim to save time and energy. But keep in mind these types of trim products can also be hard to match when you install them, and you'll pay extra for their labor-saving benefits.

2.3: Installing Polymer, Plastic or Fiber Cement Trim

Trim made from these materials is easy to assemble and has the look of wood, without wood's vulnerability to moisture. In other words, these products don't warp, twist, or rot, and they often come with long warranties--as much as 50 years. Some are formed into complicated shapes or are flexible to accommodate odd shapes or surfaces.

You can use polymer trim, for instance, to replicate intricately designed wooden trim--a popular and affordable choice for historic projects. These materials are also insect resistant and can be painted, and some are manufactured with waste or recycled content, so they're earth friendly, too. Beware, though--they cost more than traditional materials, and some come in limited sizes and shapes.

2.4: Installing Modular or Pre-Assembled Trim

New products with prefabricated corners or built-up elements that lock together make installation a snap--literally. With modular units, you don't have to have a lot of skill to replicate the craftsmanship of a bygone era. These materials usually require no finishing and are complete once they're installed. But they are more expensive than traditional trim materials, and the selection is limited. Another downside: You can't modify them to fit out-of-square openings or other irregular conditions.


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