Restoration Guide: Exterior Wall Trim

Editor's Note: This is article 16 of 18 in Chapter 2:Exterior Walls of the Old House Web Restoration Guide. This guide was developed and edited for old homes from original material in the U.S. Housing and Urban Development (HUD) Rehab Guide.

16. EXTERIOR TRIM

Section 1--Overview

In addition to dressing up a home, exterior trim provides vital waterproofing at inside and outside corners, around doors and windows, along roof edges, and at other building components. There are many different types of exterior trim on the market, such as:

• Solid wood
• Laminated wood
• Thermoplastic composites
• Engineered wood
• Fiber cement

Some of the new manufactured types of trim offer longer product life than traditional wood trim because they better withstand shrinkage and expansion associated with weatherization, ultraviolet rays from the sun, insect infestation, and rot.

Section 2--Repairing Old Wood Trim With Epoxy

Oftentimes when performing a home renovation, it's possible to salvage slightly damaged trim pieces by filling deteriorated sections with epoxy. However, before attempting any preservation of existing trim, the underlying causes that led to its degradation should be addressed and corrected.

Most decayed wood can be reconstituted using a liquid epoxy sealant that penetrates the wood's fibers and hardens. When the epoxy has set, it can be sawn, drilled, sanded, and painted. When finished, if the paint matches the rest of the trim piece, the repair may not be noticeable.

Most forms of epoxy weather well over time. Certain epoxy putties can be used with liquid epoxy to fix severely damaged sections of decorative trim--especially important in historical preservation work, where old trim pieces typically must be salvaged rather than replaced to maintain historical integrity.

Section 3--Installing New Trim

If the exterior trim has rotted to the point that it's no longer salvageable, and epoxy fillers won't prove cost effective due to extensive deterioration, the trim should be removed and replaced. Underlying causes of the deterioration, such as lack of flashing or caulking around doors or windows, need to be addressed. There are many different types of trim to choose as a replacement.

• Solid wood trim: Wood is still the builder's choice in most areas of the country for trim and fascia. The majority of wood trim is white and southern yellow pine, and Douglas and Hem fir. Western red cedar also is a popular--but more expensive--trim choice. Cedar, often sold rough-sawn, ages better than other types of wood trim. Redwood also is widely used as a fascia board. Heartwood, with its clear, vertical grain, lasts longer than other grades and takes paint extremely well. It is recommended that wood trim be primed to prevent moisture penetration. Finished sides should be protected with two coats of paint or stain.
• Laminated Veneer Lumber: South Coast Lumber, located in Brookings, Oregon, manufactures a trim with a Douglas fir core that's covered with phenolic adhesives and preservatives that protect the trim. The face of the trim is covered with a phenolic sheeting, and all edges are sealed, as well. The ClearLam trim can be used for all trim applications and fascia board.
• Engineered Wood Trim: Engineered wood trim is made from wood fibers and resins. It's manufactured similar to hardwood siding, but waxes, resins, and oils are added to the process to extend product life. Engineered wood trim can be used for corner boards, fascia, and door and window trim. Relatively inexpensive compared to wood products, engineered wood trim is an affordable choice for any cost-conscious home restoration.
• Thermoplastic trim: This trim is made from thermoplastic resins and wood fiber. It is extremely durable and is becoming a popular choice for decks, as well as for window sills and door jambs. Manufacturers such as Trex are industry leaders in thermoplastic decking and trim.
• Fiber-cement trim: Manufacturers such as James Hardie Building Products make fiber-cement trim that's often used in conjunction with fiber-cement siding (read more about fiber-cement siding in section 14 of the Old House Web Exterior Wall guide). Fiber-cement trim can be used anywhere regular wood trim is specified, and it comes in a variety of styles. Fiber-cement siding manufacturers often offer 50-year warranties against chipping, cracking, and delamination.
• Polymer trim: Made from high-density polyurethane, this trim is a cost-effective choice to replace decorative trim found in columns, balustrades, trellises, and shutters.

A house only looks as good as its trim. Damaged and deteriorated trim detracts from the natural aesthetic beauty of a home. Trim should be painted regularly to protect the material, and rotted trim should be replaced to keep a home looking its best.