Polyurethane products are playing a key role in many historical and contemporary renovation projects
By Beth Kraus, CSI, CDT
Whether one is trying to replicate the ornate trimwork from a 19th- Century Southern plantation or trying to restore exterior molding on a 1972 ranch-style home, polyurethane may be the material of choice. Widely used for both historical and contemporary residential and commercial renovation projects, polyurethane components have gained in popularity since their introduction several decades ago. Resistant to moisture, humidity, warping, splitting, splintering, insect infestation, and extreme temperature changes, high-density polyurethane is highly competitive with traditional materials for both indoor and outdoor applications.
Specifying the polyurethane spectrum
Polyurethane products range from louvers and moldings to columns and decorative millwork, with products in both structural (porch posts, and balustrades) and nonstructural (window and door trim, gable vents) categories. Polyurethane manufacturers offer a wide variety of solutions for residential and commercial renovation projects, from ornate brackets to faux beams to door pediments.
The main advantages of polyurethane are innate. The highdensity material is manufactured using a two-component rigid polyurethane foam system and has a closed-cell structure that can resist water penetration and absorption. Plus, polyurethane is a thermoset material; once the chemical reaction has taken place to form the material, heat cannot by itself revert it to its original components. This characteristic gives polyurethane foam a low coefficient of thermal expansion and contraction, which keeps it structurally stable within a wide range of ambient temperatures.
Furthermore, polyurethane products leave the factory with a consistent quality and finish, including an ultraviolet- (UV-) ray resistant topcoat that may be painted over with any good quality latex or oil-based paint. They also accept decorative faux finishes well, such as marbleizing, washing, and texturizing. In general, raw material costs for traditional products are lower than they are for polyurethane foam, but labor costs for product installation and maintenance are higher. Architects and designers interested in specifying polyurethane products for renovation projects can find support on the Web sites of various polyurethane manufacturers.1 Specially created design programs exist from all major suppliers, with several offering design configurators, computer-aided design (CAD) programs, and architectural binders. Additional resources include industry-standard calculators (for radius, rake, and bevel miter cuts) and the ability to create elevations and assemblies.
Capabilities of polyurethane millwork
Polyurethane millwork pieces can replicate intricate patterns on ceiling medallions or smooth lines on moldings. For renovation projects, one of the material’s chief assets is its ability to gain highly detailed, authentic-looking reproductions of historic forms. Heavy, ornate, plaster ceiling medallions can be replicated in polyurethane pieces weighing less than 0.45 kg (1 lb). For those projects requiring the look of traditional materials, many manufacturers offer stainable polyurethane moldings containing authentic wood grains.
The closed-cell structure of polyurethane products can make them suitable for high-humidity areas of the home, such as bathrooms, kitchens, and laundry rooms. Wall niches, moldings, and brackets are popular in these rooms because they neither warp nor twist when exposed to excessive moisture. Throughout the rest of the home, polyurethane products can be found as window and door trim, ceiling domes, faux beams on ceilings, and one-piece mantel surrounds. Low-maintenance polyurethane shutters, louvers, and entryway surrounds are extremely popular on the exterior of residential projects and are generally available in dozens of styles complementing all major designs.
Nonresidential renovation applications of polyurethane products are abundant. From refurbishing classic millwork in restaurants, offices, and healthcare centers, to replacing balustrade systems in college dormitories, nursing homes, and hotels, polyurethane is selected for a wide variety of commercial projects.
What once may have been an arduous task of specifying historically accurate reproductions of moldings can now be accomplished more quickly. Polyurethane companies possess profiles that can be used to custom replicate even very ornate architectural designs. Some of the most popular moldings include dentil profiles, cornice-and-cove, crowns, chair rails, and window/door trim. More elaborate egg-and-dart, crown leaf, ribbon-and-bow, Florentine, and scalloped molding profiles are also available. Special collections of styles, including Victorian, Arts-and-Crafts, Southwest, and contemporary moldings and millwork are also available, as well as accessories including miterless corners, plinth blocks/rosettes, keystones, and molding divider blocks. Upon requesting custom pieces to fit around, say, oversized door entries and windows, an in-house fabrication shop at polyurethane production facilities would fulfill the order, saving time and labor on site.
One innovation applauded as a time saver by both specifiers and installers is the polyurethane eave vent system, which acts as both a decorative molding profile and a functional vent that can prolong roof shingle life. Structures using these systems often contain functional louvers—a combination of polyurethane louvers featuring slats with steep 45-degree angles that also include noncorrosive screens to help keep insects out while allowing airflow. Material limitations and building codes
Although many polyurethane products are solely decorative and have little structural integrity, other applications provide a greater support role, such as porch posts, balustrade systems, and columns constructed with supporting interiors made of fiberglass, polyvinyl chloride (PVC), or steel.2
Some companies contract certified laboratories to independently test load-bearing capabilities of structural components. Although many manufacturers follow International Building Code (IBC) guidelines to test rail systems, there are no established guidelines for testing their load-bearing capabilities. Some manufacturers test these pieces to a load at which the amount of force being applied stops increasing and levels off. From that number, a safety factor of 1.75 to 2.00 is used to determine the load capacity.
Building professionals will find that most polyurethane products can be used in accordance with specifications that are in the International Code Council’s (ICC’s) I-codes and that are defined by the National Fire Protection Association (NFPA). Some balustrade systems meet the National Building Code’s (NBC’s) 1993 Criteria (1615.8.2 Guard Design and Construction, and 1622.214.171.124 In-Fill Areas), when assembled according to manufacturer guidelines. These codes are met based on the way the balustrade system is assembled, not necessarily on the polyurethane product itself. Manufacturers assemble the balustrade systems according to the installation guidelines they print in their catalogs and then test these same systems to check that the pieces comply with code rulings.
While polyurethane millwork products are suitable for varied climates, they should never be stored for long periods in extreme heat, which can cause distortion and warping. Most polyurethane millwork can withstand about 60 C (140 F), but prolonged exposure to temperatures beyond 93 C (200 F) can result in the deterioration of the polyurethane foam’s physical properties. At this point, the product will begin blistering on the surface—especially if the piece has been painted a dark, light-absorbing color. But as mentioned previously, polyurethane is a thermoset plastic and will neither melt nor revert to its original components.
As with most building products, polyurethane pieces should acclimate for approximately 24 hours to their installation environment prior to application. Due to the temperature warping described above, polyurethane millwork should never be specified in an area subject to solar temperature buildup, such as behind a storm door.
While some manufacturers are currently working toward meeting the flame-spread tests in ASTM International E 84, Standard Test Method for Surface Burning Characteristics of Building Materials, most polyurethane millwork products are not specifically formulated for fire resistance. Therefore, specifiers are encouraged to check with individual manufacturers for flameresistance restrictions and special product orders that meet Class 1 ratings. In all cases, local building codes should be consulted and followed when using polyurethane or any other building product in a project.
Case studies and examples
While the primary use of polyurethane products is for decoration, there can be cases where millwork solves design problems. For example, to help create a stately exterior for a Providence, Rhode Island, assisted-living center, the design team specified an expansive array of polyurethane balustrades, corbels, and detail work on the building exterior. The pieces added the necessary structural and decorative accents to replicate the look of the original mansion. In a similar situation in St. Louis, Missouri, a designer challenged with the replication of cracked and decaying plaster molding in a historic hotel ballroom turned to polyurethane. The manufacturer was able to create a perfect historic match to the existing millwork. Although the polyurethane product was added to the room alongside the original plaster, the difference between the materials was hard to see.
Notes 1 Specifiers interested in gaining more information on the polyurethane industry can also find weekly updates from Urethane Update—Polyurethane Abstracts. This online newsletter, available at www.pu2pu.com, offers information on the latest patents, technical papers, product information, and technical aspects affecting the polyurethane industry. 2 Since there is no distinct advantage of any of these structural materials when used in conjunction with polyurethane, the support material is determined by the application and manufacturer.
Beth Kraus is district sales manager for polyurethane millwork manufacturer, Fypon.