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. With the arrival of HVAC (Heating
3 JOURNAL
Window Replacement Project Existing Windows
Sealant failure at window exterior. Damaged flashing at window head. Water intrusion and interior damage. Replacement Process Completed Project
Window removed; wall opening ready Installation of replacement windows. for replacement window installation.
Installation of new flashing at win- Reconstruction of brick exterior wall dow head. after flashing replacement.
Ventilation Air Conditioning) systems, usually accompanied by water entry, thermally improved windows can rival windows have become only a second- can be signs of compromised glazing, the insulation value of a stud-cavity ary or emergency means of ventilation. perimeter seals, or weather stripping. wall. But rising energy costs aren’t the Moreover, in order to maintain HVAC only reason to address thermally de- system efficiency, windows need to Thermal Performance ficient windows; exposure to exterior remain air-tight to minimize heat and With the advent of Insulated Glass temperature and humidity fluctuation humidity transfer. The same seals that Units (IGUs), Low-E coatings, and other through insufficiently insulating win- protect against moisture infiltration heat-conserving developments, today’s dows carries a risk of damage to inte- also guard against unwanted air trans- window technology has become riors due to condensation. Moisture in fer. Drafts observed near windows, advanced to the point where high-end the air will condense on any surface in
4 V O L U M E 2 5 N U M B E R 3
a room colder than a specific tempera- Building location. In general, factors to ponents, such as roofs, awnings, cor- ture, or dew point, which is associated consider for the exposure of a building nices, decorative elements, or balconies. with the relative humidity. Windows include: Even the degree to which a window with poor thermal performance readily • the height of the building relative to is recessed into a wall cavity effects its conduct cold ambient temperatures, other adjacent buildings, exposure risk, because rain and snow leading to moisture condensation on will drain clear of a recessed window. windows and surrounding surfaces, and, • the density of the surrounding build- Below the window, architectural fea- eventually, water damage and possible ings, and tures such as sills, ledges, terraces, and fungal growth. • the geography and topography of other elements can contribute to the The occurrence of condensation the area, such as the climate and possibility of moisture infiltration from may merely be a sign that the inte- proximity to the coast. standing water or snow drifts at the rior is being maintained at high heat In addition to the general exposure base of the window. and humidity when it is cold outside. characteristics of the building as a Noise exposure. Especially in dense However, under normal conditions, whole, each individual window is urban areas or adjacent to noise-pro- frequently occurring condensation is a subjected to a unique set of environ- ducing equipment, windows’ level of sign that the windows are performing mental forces which impact its risk for noise control can be a critical perfor- poorly with respect to thermal insula- deterioration. mance criterion for occupants’ comfort. tion. Check the accompanying table to Window orientation. When review- Lateral forces. In some orientations determine the most likely explanation ing windows for water infiltration, the and locations, wind pressure and suc- for recurring condensation in various design team must consider the prevail- tion forces can be severe enough to locations on the window assembly. ing direction for wind-driven rain, as compromise a window’s structural Window Exposure windows in that orientation are at a integrity or capacity for air infiltration One of the most important consider- much greater risk for moisture ingress protection. Some warning signs in- ations for evaluating existing windows than are leeward facing windows. clude: cracked glass, misaligned frames, and scheduling repairs has nothing to The orientation of a window is also difficult operation, and heavy drafts. important to thermal performance do with the window itself. The loca- Fire exposure. To insure that windows evaluation, as exposed windows on tion of a window on the façade and adequately protect against the spread a south façade receive considerably its exposure to the exterior elements of fire, building codes and zoning more sunlight than do windows on the must be considered when determin- ordinances establish a fire separation north face. ing the window’s risk for damage and distance, or space between buildings. deterioration, or when assessing any Overhang protection for windows can Depending on this distance, building deficiencies in its performance. be provided by various building com- codes also dictate the allowable area of
Investigating Condensation
Moisture Location Probable Deficiency
On the interior surface of the window Inadequate thermal performance of glazing unit
Between the panes of an Insultated Failed hermetic seal Glazing Unit (IGU)
On the window frames Missing or insufficient framing insulation or thermal breaks
5 JOURNAL
protected and unprotected wall open- posed window meets or exceeds ing is often needed near conventional ings, taking into account additional fire the current standard for each windows, where heat loss is great- resistance measures, such as sprinkler performance criterion. est. In buildings in which thermally systems. Window assemblies and 4. Check building codes. New efficient windows have been installed, materials that have been fire tested are and rehabilitated windows must perimeter heating may no longer be considered protected openings. Your meet code regulations for the necessary, and demand on mechanical design professional can establish how performance characteristics listed systems can be reduced overall due to the building code and adjacent build- above, as well as for fire resistance, lower peak heating and cooling loads. ings affect your windows. emergency egress, energy conserva- Another reason to consider redesign- tion, and wind resistance. Minimum ing windows is to reduce electricity Window Selection Criteria performance standards and ap- consumption. A window replacement Selecting new windows can seem plicable codes vary depending upon project offers an opportunity, where daunting, as there are countless alter- the authority having jurisdiction over structurally feasible, to enlarge glass natives from which to choose, but sys- the project; consult your architect area, admitting more daylight into the tematic review of window needs and to guide you through this process. building interior. This daylighting in options can reap long-term rewards. Historic or landmark structures turn reduces the need for artificial il- may have additional restrictions on lumination, enabling some lights at the 1. Review the wall system construc- window rehabilitation options. For building perimeter to be switched off tion. Determine whether the applicable regulations, check with during the daytime. windows are to be curtain wall, the local historic preservation com- storefront, window wall, or punched mission. windows; the selection will often be Occupant Comfort determined by the window opening 5. Determine design goals. Selec- Daylighting has become a hot topic in sizes, the structural requirements for tion of new windows provides an environmentally sound building design the windows, and the cost differ- opportunity to make more dramatic not only for its reduction in energy ences between types. Evaluate the functional and aesthetic changes to consumption, but also for its impact existing conditions of the surround- the building envelope. Reconfigur- on building occupants. Attention ing building elements, such as lintels, ing the fenestration can open up has been paid in recent years in the flashings, and exterior wall materials, glass area for greater viewing range, scientific and architectural literature to determine if they are watertight. improve window operability for bet- to the positive effects of natural light ter passive ventilation and reduced 2. Select the frame materials and on health and productivity, but the drafts, and update the overall exte- window type. Consider with the importance of connecting interior rior appearance of the building. architect the pros and cons of each spaces with the cycle of the sun has material and window type that can been incorporated into building design be installed on the building. Once Energy Considerations for centuries. a selection has been made, it is Windows are the modulators of heat, More might seem to be better when important to discuss frame finishes. light, and air. At the perimeter of a it comes to visible transmittance and Today’s windows have a wide vari- building, their effect on the interior window selection, but large, non-tinted ety of available finishes, with a broad environment can be significant. High- windows on a west-facing computer color palate, as well as performance performance windows reduce both center might mean increased interior characteristics such as fade and heating and cooling costs by prevent- temperatures and closed blinds for half scratch resistance. ing heat transfer, and they also provide the day. Care must be taken to balance 3. Consider window performance more comfortable surroundings for building use with glare control, heat ratings. Generally the main criteria occupants by stabilizing the tempera- moderation, and light distribution to for the performance of a window ture throughout the interior space. achieve a pleasing indoor atmosphere. are structural capacity, ventilation, Installation of higher-insulating win- waterproofing, light transmittance, dows can mean reductions in both the A Window’s Work Is Never Done and thermal and acoustic insulating size and output of heating and cooling Windows have a greater impact on capacities. The window manufac- systems. While a majority of heating is the comfort of occupants than does turer should be able to provide test provided by central HVAC systems in results confirming that the pro- commercial buildings, additional heat- (continued on page 8)
6 V O L U M E 2 5 N U M B E R 3
Windows Art and Architecture Building Hoffmann Architects specializes in Yale University remediating distress and failure at build- New Haven, Connecticut ing exteriors. Because windows are Landmark Window Replacement particularly prone to water and air in- Consultation: filtration, they require special attention. Investigated window failure and collabo- Hoffmann Architects’ design team un- rated on new design. derstands the critical interplay between Various Fairfield Public Schools windows and other façade elements. Fairfield, Connecticut As such, project teams treat windows Window Rehabilitation: not as isolated units, but rather as a Provided investigation, restoration, fenestration system which depends, replacement, and maintenance master both aesthetically and structurally, on planning services. related building components. Hoffmann Architects has worked in a Scholastic Inc. Global Headquarters variety of capacities on window projects. New York, New York A sampling: Landmark Window Rehabilitation: Restored antique windows and designed Burr Hall Former Southern New England historically accurate replacements where Eastern Connecticut State University Telephone Headquarters in New Haven, needed. Willimantic, Connecticut Connecticut. Historic Window Refurbishment: The Bank of New York Window Replacement: Restored steel windows to preserve historic New York, New York Addressed deterioration and water infil- materials and provide cost savings. tration conditions and improved efficiency. Window Investigation: Addressed heat loss from 1,500 original Rockefeller Center Complex Schering-Plough Buildings steel windows. New York, New York Summit, New Jersey Weathertightness/Air Infiltration/Cost- Window Replacement: Benefit Study: Mitigated air and water infiltration and Analyzed over 40,000 windows in 12 improved heat retention. buildings. Pfizer, Inc. World Headquarters Various New York City Public Schools New York, New York New York, New York Window Replacement: Window Failure Investigation: Upgraded lot-line windows for high- Inquired into premature deterioration of performance-demand exposure. Folger Shakespeare Library in Washing- replacement windows. ton, District of Columbia. Historic Window Verizon Communications Assessment: Evaluated eleven window types for The Sheffield New York, New York efficiency, waterproofing, and finish integrity. New York, New York Window Replacement: Window Consultation: Rehabilitated leaks and inefficiencies at Addressed recurrent water infiltration. fourteen buildings.
7 JOURNAL
(continued from page 6)
Where Is This Water Coming From? JOURNAL is a publication of Hoffmann Architects, Inc., specialists in Possible sources: the rehabilitation of building exteriors. • Misaligned or The firm’s work includes investigative corroded frames. and rehabilitative architecture and • Cracked or loose engineering services for the analysis seals. and resolution of problems within • Irregular weather roofs, facades, glazing, and structural stripping. systems of existing buildings, plazas, • Gaps in joints. terraces and parking garages. Water pooling at sill. Stains on frame. • Loose fasteners. Please send news, technical information, Possible sources: address changes or requests for free • Missing or damaged subscriptions to Editor, Hoffmann flashing. Architects JOURNAL, 2321 Whitney • Faulty perimeter Avenue, Hamden, CT 06518. sealant. • Blocked weep holes. For information on the services • Wall system failure. offered by Hoffmann Architects, Inc., contact our Marketing Coordinator at Interior finish damage. Exterior finish damage. 800-239-6665 or:
2321 Whitney Avenue Hamden, CT 06518 any other building element. Acting as Because the optimal performance of 203-239-6660 “gatekeepers,” they permit entry of windows is essential to building func- desirable exterior forces (light, air), tion, replacing improperly installed or 500 Fifth Avenue, Suite 830 while locking out undesirable ones selected windows or updating inef- New York, NY 10110 212-789-9915 (water, cold, heat, noise, pollution). ficient windows can dramatically impact They must withstand the pressures building operation overall. Whether 2611 Jefferson Davis Highway, Suite 200 of wind, ice, temperature fluctuations considering current trends in sustainable Arlington, VA 22202 and extremes, and ultraviolet radiation, design or ancient principles of interior 703-253-9800 while remaining ever beautiful, ever to exterior relationship, you’ll find that For more information on the topics youthful, ever fluidly operational. With windows provide much of a building’s discussed in this article, visit us on the such continuous and critical demands, vitality and ambiance. Making their web at www.hoffarch.com or contact windows need attentive care and proper function a priority is an invest- us at [email protected]. maintenance in order to meet these ment in the integrity and sustainability Editor: Alison Hoffmann challenges without distress or failure. of building systems—inside and out. Production: Margaret Bailey
Hoffmann Architects, Inc. 2321 Whitney Avenue Hamden, CT 06518
ADDRESS SERVICE REQUESTED