The view of your window is not always the same: Proper window installation is an investment

Similar to a chain, a building envelope is often only as strong as its weakest link. Specifiers often expend a lot of time on exterior wall detailing, more specifically with respect to the materials, drainage, flashing, etc., paying only little attention to the window product and installation requirements. The marketplace offers many varieties of windows. In practice, we see those windows installed into even more varieties of building construction, with an equal number of variations in installation practices and material selection. Divergences and variations from good practice, code requirements and accepted standards cause everything from unnecessary air infiltration to catastrophic damage to buildings as a result of underperforming windows. The attention of a specifier to Building Code requirements and accepted Standard Practices, as well as voluntary practices, can go a long way in the ultimate performance of the building envelope. There are several primary references that must be considered in window specification. These include, but are not limited to: Local Building Code, Local (city) Ordinances, ASTM E2112, ASTM E330, and AAMA Voluntary Specification. Local Building Codes must be referenced as they are often based upon a national code such as the International Building Code (IBC), but may have specific requirements in certain geographical areas that result in stricter requirements for installation/specification. Each geographic area may also have specific energy compliance requirements to follow. Specific installation may also require special structural consideration, fire resistant consideration, and unique waterproofing detailing. Most specifiers commence with the material selection. The material selection will be based upon cost, aesthetics and performance requirements. The material selection options for a single story ranch house 120 miles inland from the ocean are much greater than those of a 20 story ocean front high-rise. For example, as of the date of preparation of this article, the writer is not aware of any vinyl windows that would meet the structural requirements for an ocean front high rise; however, a residential home outside of a high wind area will have a much smaller wind load. Therefore, product options include vinyl, wood, aluminum, aluminum-clad wood, vinyl-clad wood and even fiberglass. Each of the different products has its variations in application as well as its benefits. Regardless of the material selection and the design standard, the specifier must anticipate that all windows leak. Windows are only tested and designed for specific conditions, so when the conditions exceed those design standards, there is a potential for water infiltration through the window. There are a lot of conditions that can affect whether or not the window fails under a given in-situ condition. These conditions include the exposure of the window, the loads induced on the window (noting that the geometry of the building and the location of the window in that geometry can have a significant impact on the loads induced onto one window versus another window in the building), and the exposure of the window to elements (is the window recessed into the building, or is the window flush with the building?). Yes, all windows leak; therefore, a specifier should also anticipate in the design where the water will end up after it has made its way through the window. Also important is the integration of the window with the weather resistive barrier (WRB) of the building wall, if one exists. The window flashing at the sill, head and jambs (bottom, top and sides respectively) must be properly integrated with the WRB. Finally, sealants necessary to seal the window to the adjacent building materials must be properly designed and installed. Proper design of sealants includes anticipating the width of the joint based upon the calculated thermal movement of the window and selecting a sealant material that can handle the movement. To rely on the performance of a window installation that depends solely upon use of sealant materials for moisture resistance is placing one's hope for the window's moisture resistance on the installation's weakest link. The fact that the sealant will weather and eventually fail is a given. The fact that the sealants and gaskets in the window will age and fail is also a given. By installing secondary barriers that collect and return the water to the exterior, the building will have an increased resistance to water infiltration. Proper installation as outlined herein, as well as proper selection of materials, can be a wise investment and, in some cases, a code- required investment toward a problem-free building envelope in the future. William Pyznar, P.E. is a principal at The Falcon Group, Bridgewater, N.J.