ISSUE 3/2008 V O L U M E 2 5 N U M B E R 3 Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Windows: An Integral Part of the Building Envelope Juan Kuriyama, AIA and Bradley Carmichael, EIT With the reports from recent tion options may be limited by any clinical research substantiating the number of factors, from landmark importance of natural lighting and regulations to structural limitations to ventilation in workplace productivity, aesthetic concerns, within these limits it health, and well-being, window design is often possible to improve energy effi- has become about more than building ciency, optimize light transmittance, and aesthetics or even energy efficiency. shape building appearance both inside From the capacity to create dramatic and out. And, because deterioration in gestures in glazing afforded by glass one building component can adversely curtain wall technology, to the im- affect interrelated components, ad- provements in thermal transfer made dressing distress or inefficiency in the possible by chemical advances in the fenestration not only will impact other glazing industry, to the race to develop building systems, but, as new research carbon-neutral strategies like “day- has touted, will shape one critical part lighting” that reduce demand on the of the building dynamic: the occupants. power grid, windows have taken on multi-faceted significance in building A Window Components Primer design. Even from humankind’s earli- est attempts at creating boundaries, Before considering rehabilitation op- we’ve found that our most successful tions for existing windows, it’s impor- efforts establish meaningful connec- tant to know the composition and tions between inside and outside, properties of the existing wall system, which establish our control over the so that an appropriate, compatible delimited structure by contextualizing repair or replacement design can be developed. An architect or engineer Whether the goal is historic preservation that order against the vastness of the experienced in window rehabilita- or an aesthetic overhaul, window rehabilita- world beyond. tion can determine the structural and tion improves appearance while optimizing While it is tempting to give little material properties of your windows, performance. thought to existing wall openings as well as their condition, through an beyond immediate maintenance investigation. To assess your options, demands, periodic window repair or the design team will consider: replacement projects are an opportu- nity to rethink the window design and Wall System Construction to determine if the existing system In contrast to a glass curtain wall, meets the needs of the structure as a which supports only its own weight, whole. Although window rehabilita- not that of the building structure, and As Senior Architect with Hoffmann Architects, Inc., Juan Kuriyama, AIA has specialized expertise in window reha- bilitation, directing projects from investigations to design through construction administration. Project Manager Bradley Carmichael, EIT has experience in all phases of window investigation, repair, and replacement. JOURNAL Double-hung Casement Sliding Awning is composed mainly of glass units carries the load of the window into dow types, classified by operability: anchored to a frame, a punch open- the wall below. Single or double hung. Two sashes ing, or exterior wall opening, is an open • Jambs. The vertical wall sections that slide vertically in adjacent planes. space in an exterior wall around which to each side of the opening, which “Single hung” refers to one oper- the weight of the wall is directed. The carry the load transferred by the lin- able sash, “double hung” to two. opening can remain unobstructed, as tel into the wall below. Depending Taller openings may have triple hung on a balcony or terrace, or can be upon the size of the opening, they windows. Although familiar to many filled with a window, louver, door, or may need to be reinforced. homeowners, this window type is storefront. Whether your building is also widely used on high rises, due to constructed with load-bearing walls Window Type its ease of operation and good wind and punch openings or glass curtain If you own a home, you’ve probably resistance. walls will determine which options are heard of “double-hung” and “case- available for retrofit or rehabilitation. ment” windows, as well as “vinyl Sliding. Operate like their single- replacement windows.” These terms or double-hung cousins, but slide For the purpose of this article, we will represent two methods of classify- horizontally, rather than vertically. consider not the glazed curtain wall, ing windows: by operability and by Maintenance of track hardware to which has its own considerations and framing material. The first two terms remove dust or accumulated particles options, but the standard punch open- refer to the manner in which the is critical for proper operation. ing window. The basic components: operable panes, or framed sheets Casement. One or more sashes that • Lintel. The horizontal section at the of glass, move relative to the frame, swing outboard or inboard from the top of the opening, which distrib- or fixed portion of the window. vertical frames. Although common utes the load of the wall above the The frame structurally secures the on residential applications, consider- window into the vertical sections window to the perimeter of the wall ation must be taken with high-rise on both sides. To accomplish this opening, while the panes support the commercial use, because the sash and structural task, the lintel employs one glazing. Spacers, seals, gaskets, and hardware have lower wind pressure of various types of arches, or it man- other accessories used to fit the glass tolerance. ages the load via sturdy materials, within the frame are also considered such as structural pre-cast concrete, part of the glazing, not just the glass Awning. One or more sashes that reinforced cast-in-place concrete, sheet itself. Depending upon the swing outboard from the upper stone, or steel angles. The lintel style and operability of the window, frame. Their name derives from the system also serves as a water infiltra- various hardware elements, such as weather protection offered by the tion barrier by means of flashings. locks, weights, balances, handles, stops, window in the open position, when hinges, or weather stripping, complete it creates a canopy-like projection • Sill. The horizontal section at the the system. above the opening. bottom of the opening, which pro- tects against water infiltration and An overview of some common win- Hopper. Operate like the awning 2 V O L U M E 2 5 N U M B E R 3 Curtain Wall Historic Steel Fixed style, but swing outboard from the sity, and difficult maintenance (due to Identifying Problems lower frame, rather than the upper one. possible corrosion) have substantially When an architect or engineer evalu- reduced its prevalence. Nevertheless, Pivoted. A single sash that rotates ates an existing window, he or she will steel windows have found their role in around a vertical or horizontal axis first establish the style and composition the industry whenever fire resistance centered on the frame. Easy to clean, of the window system, then investigate is required. but offer little resistance to wind common sources of trouble typical stress. Wood. Also used in the past on to the type of window assembly and Fixed. Do not need operable hard- commercial applications, especially on materials. In general, the architects or ware, and so achieve the maximum large institutional or educational build- engineers will look for: glass area for a given opening. Also ings. In both replacement and new known, more familiarly, as “picture construction, aluminum windows are Water Infiltration Catching leaks early. Water infiltra- windows.” now usually specified in place of wood. When wood windows are chosen, it is tion can be as minor as small droplets Framing Material generally for aesthetic reasons, or for on the interior after a storm, or as All of the styles of windows reviewed replacement of historic windows in major as ongoing moisture intrusion above can be made from a variety residential and light commercial appli- that leads to structural degradation of materials, so it is important when cations. Wood windows have a good and mold issues. In both instances, it is critical to determine and address the assessing both existing windows and reputation for thermal and insulating root cause of the water entry, because replacement and repair options to qualities, but proper maintenance and even a minor leak over time can begin consider not only the operability of care to reduce exposure to moisture to cause serious damage. the window, but its material composi- are crucial to avoid rapid deteriora- tion, as well. tion. Wood frames can also be clad Finding the source. Moisture-related Aluminum. The most widely preferred with vinyl or aluminum. failures can occur in the window itself, in the rough opening around the material for commercial applications Vinyl. Made from polyvinyl chloride window perimeter, and sometimes due to its low cost, versatility, light (PVC), a rigid and tough material ex- in the adjacent wall assembly entirely weight, ease of maintenance, broad truded to form the window elements separate from the window. It is a availability, and variety of finishes. at a reasonable cost. Vinyl offers good idea to have a building envelope Aluminum windows have a poor good sound and thermal insulation reputation for thermal integrity, which consultant confirm the source of the properties. However, limitations on failure, so that the most appropriate has been addressed by incorporating size and finish colors, vulnerability to thermal breakers. repair program can be developed for fire, sensitivity to extreme cold and to the window or windows in question. Steel. Although broadly used before ultraviolet light, and difficulty with re- the development of its aluminum finishing have limited vinyl window use Ventilation counterparts, steel’s higher cost, den- primarily to residential applications.