Wood Doors: A Lesson in Performance

by Jim Brandt, Simpson Door Company

The building industry's increased emphasis on energy efficiency and the implementation of stricter energy codes is driving builders, architects and homeowners to find higher performing building components while maintaining aesthetic appeal. The current energy crisis in California and along the west coast has only enhanced the energy efficiency microscope.

Consumers are taught to look for special rating labels such as Energy StarÒ and to research a product's energy performance ratings. By selecting the right building product for the climate and environment, a homeowner can enjoy incredible energy cost savings. While most of the focus of energy efficiency is on products that cover a large surface area-walls, roof and windows, for example-there are also performance differences among smaller building products such as doors.

The majority of heat loss in an exterior door system occurs around the door and not through the door. Therefore the most important solutions for increasing energy efficiency lie in how well the door has been hung and the quality of the application of weatherstripping. Some of the factors responsible for door performance-materials used, construction process and the use of glass-are examined in the following paragraphs.

Fortunately, nature provides for us the most energy efficient building material: wood. According to the Temperate Forest Foundation, wood is 16 times more efficient as an insulator than concrete, 415 times as efficient as steel and 2,000 times as efficient as aluminum. Wood door panels are also much thicker today than in year's past. Door panels were once as thin as 7/16" or 9/16," but today's panels range from ¾" to 1-7/16" thick. In addition to improving efficiency, the thicker panels also improve the depth and beauty of the door's natural wood and grain characteristics.

Throughout the past decade, door manufacturers have taken great strides to take wood's natural insulating characteristics and use them to make better performing doors. They have developed more efficient manufacturing processes and better construction and engineering techniques. Before constructing their doors, for example, Simpson Door Company uses precise lumber drying techniques. Lumber drying involves much more than simply drawing the moisture out of the wood. Tensions and stresses in the lumber are also relieved in the drying process. And the drying cycle time plays a critical part in ensuring the dimensional stability of each component part of the finished door.

Other significant developments include enhancements in the construction of panels, stiles and rails. For example, wood has a natural tendency to expand and contract with changes in temperature and humidity. In the past, such fluctuation frequently created problems with surface splits or stile and rail separation. Today, manufacturers build doors with "floating" panels, held in position by grooves along the edges of the stiles and rails instead of glue. This allows for more movement and eliminates splitting and separation.

Today's wood panel is also manufactured to face challenging conditions. It is first sliced into sections and then one of the sections is rotated 180° and bonded to the other section. The opposing grain patterns and the glue reinforcement greatly strengthens the unit and results in a panel that will stay true and will not split through.

Stiles have also evolved dramatically. Rather than using a single, solid piece of wood, many manufacturers now construct a stile with several shorter pieces of lumber bonded together and covered with a fine grain veneer. The core pieces are fingerjointed and the offsetting grain patterns are glued together, providing greater resistance to warping and twisting. Consequently, the stile will retain its shape better, regardless of the climate. And when a veneered stile is placed in a panel door, it's virtually impossible to notice any difference from a stile made of a single piece of wood.

Covering the core with a veneer also allows manufacturers to control and maintain higher standards in the surface appearance of the doors. Grain flaws in the core can be hidden and the best looking wood can be stretched further, creating greater consistency in the beauty of the doors. Resource conservation is also a benefit derived from the engineering process. Manufacturers can stretch their lumber supply by utilizing each piece of lumber where it works best, whether as a core piece or veneer. This results in far less waste.

Some manufacturers have elevated their construction processes an additional step by taking on what has historically been the most challenging environmental condition that wood doors face: high exposure to tough weather elements such as rain, snow, direct sunlight and standing water. These conditions have caused problems such as swelling, splitting, rotting and warping in wood doors.

Simpson Door Company, for example, set out to enhance the performance of wood doors in extremely difficult conditions without altering the door's exterior appearance. While it is commonly known that most water damage to wood doors occurs in the bottom rail, Simpson decided to examine this issue more closely. The company set out to determine exactly how water infiltrates this portion of the door and how to block it effectively. After extensive research, Simpson discovered the infiltration pattern that leads to problems such as leaking, rotting, warping and separation. Simpson found that the source of these dilemmas were at the bottom of the stiles and then developed a solution to solve these issues.

Simpson developed a new defense system-UltraBlockä technology and an exclusive Weather Sealä process-that blocks water absorption and preserves the wood's natural appearance. UltraBlock is literally a 4" block of moisture-resistant material in the bottom of each stile that is then covered with a wood veneer. The Weather Seal process provides added moisture protection at the stile and rail joints. When the stile and rail are assembled, the joint is glued and secured with a dowel pin. A special seal is applied to the end grain of the rail in order to resist moisture penetration.

Together, UltraBlock technology and the Weather Seal process help prevent moisture from entering the stile end and seeping into the bottom rail, making the door resistant against moisture-related problems. Using this practice, Simpson developed a product line made for battling the toughest elements: Performance Seriesä doors. Performance doors are recommended for patios, waterfront doors, wet climates and areas with poor overhang protection.

Many of today's door choices include glass. Glass is immensely popular, for it can add depth and individual character to a door. In the past, using glass in doors often gave a perception of poor energy performance. Now there are a number of glazing options that make these performance concerns insignificant. Increased space between glass panes, low-emissivity film coatings and argon gas have all contributed to more energy efficient products. Additionally, manufacturers now sometimes place U-shaped steel spacers between the glass panes instead of the traditional box-shaped aluminum spacers. The change in material and new shape greatly reduces conductivity, thereby improving energy efficiency.

Some manufacturers now offer triple glazing in their leaded glass doors. The leaded glass is sandwiched between two sheets of clear, tempered glass and the edges of the glass are then sealed together to form an airtight unit. This strengthens the decorative insert and makes it more energy efficient, without compromising aesthetic appeal. The smooth surface also simplifies cleaning and maintenance.

Manufacturers continue to research and develop new processes and products. At no other time in history have doors performed so efficiently. The natural beauty of wood doors has made it popular for centuries, and with new technological developments now available that preserve this look, wood doors will continue to be a favorite for years to come.

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