Architectural Glazing Practices

Home , Glazing (window), Hoffmann Architects

third issue 89

Preventing problems with glazed curtain walls

By Robert G. Spindler

Aluminum curtain walls for commer- high performance reflective glasses, the materials used in the glazing chan- cial office buildings began to evolve sealants, gaskets and other materials nel are affected by ultraviolet light, in the early 1950's. Today these glass used in the glazing channel are expos- these materials most likely will and metal building facades have pro- ed to considerable temperature ex- degradg producing costly repairs on ven themselves cost-effective, tremes and high concentratíons of the project. aesthetical ly pleasing, energy efficient ultraviolet light. Temperatures of and capable of per{orming under monolithic reflective glass in spandrel Chosen glass materials must meetthe stringent environmental conditions. or nonvision areas have been architect's specifications for perfor- Architects continue to design unique measured at 1900 F. This imposes con- mance, which usually are: structures with innovative concepts re- siderable expansion and high . Glass thickness and type (an- quiring, at times, the building temperature resistance requirements nealed, heat treated) to meet materials to meet extraordinary on all materials that come in contact specified and wind load specifications. With the advent of new with the glass. Depending on the type requirements, materials and philosophies in ar- of glass, significant amounts of o Thermal efficiency requirements chitectural design concepts, the total ultraviolet light can be reflected from for both summer and winter curtain wall, including metal, glass, the glass into the glazing material. lf conditions, sealants and gaskets, has had to per- o Aesthetic requirements, form under a variety of conditions; . Class type to resist the potential namely, thermal environment, of breakage due to thermal stress negative and positive wind loads, wall conditions, and system dead loads, water penetration, o Building codes. and air infiltration. The design of a properly functioning curtain wall system requires specific consideration GIass and Shading Devices of the glass retaining system or glazing members. Draperies, blinds or other interior shading devices must be hung so as to provide space either at the top and bot- Glass Considerations tom or one side and bottom to permit natural air movement over the room With advent of heat absorbing and side of the glass, Figure 1 depicts the

volume 7 number 3 copyright Hoffmann Architects 1989 I

.10 criteria that should be metto avoid for- tion at low temperatures may impose of over pounds per inch should be mation of a heat trap. The use of heat significant stresses on glass, sealants avoided. treated glass may be necessary to off- and gaskets. set the effects of a lack of adequate vent¡lation. The metal framing system must Glazing Guideline Dimensions uniformly support the glass. The glass industry has set guidelines that the The glazing system should provide for framing needs to be within limits for minimum face clearances, edge bow, squareness, and corner offset as clearances, and nominal bite (Figure indicated: 2). Adequate edge and face clearances will properly cushion the glass, ther- o Bow - 1/16 inch in any four foot mally and mechanically isolate the length of framing; glass framing members, and prevent . Squareness - 1/B inch difference glass to metal contact. A nominal bite l-1t2" in the lengths of the diagonals of on the glass will provide adequate l-1r2 (37mm) the frame; glass retention without excessive glass Minimum o CornerOffseL-1/32 inch ateach coverage. Excessive glass coverage can Glass Clearance corner, increase thermal stresses at the glass edge. The glass industry has also set t- guidelines on glass framing member Venetian Blind deflection under design loads. This Setting Blocks 2'(50mm) Drapery or 2 guideline states that Minimum Roller Shade to minimize the Clearance potential for glass breakagg the glass Glass lights should be set on two 80 surround should not impose any ben- to 90 durometer neoprene setting ding or high concentrated com- blocks positioned the quarter 1-1t2' at pressive loads on the glass and should points. When this is impractical, the not deflect more than 1/l75th of its span under loading or 3/4 inch, Air Flow whichever is less. ln addition, the glazing system chosen should isolate the glass from other parts of the wall. à Figure 1. indoor shading and heat duct Iocations

1. Minimum 1-Vz" clearance required top and Sealant and Gasket Considerations bottom or one side and bottom between b shading device and surrounding construction. Sealants and gaskets must withstand 2. Minimum 2" clearance between glass and the anticipated shading device. movement of members

3. Heating/cooling outlets must be to room with which they come in contact, be SEÍ|NG BLOCKS (2 per sill) side of shading device. compatible with other materials being

used, retain their properties after ex- WEEP YSTEIV{ {3 ær sil) posure to anticipated environmental (a) (b) (c) Metal Considerations conditions and not impose any undue OreEll Face Blte Edge Thlckness C eaËnce C ea6nce stress on the glass. Gaskets should be Because the coefficient of thermal ex- designed so Monol¡thlc that the section contacting G aas tla" elø" 14' V4 pansion for aluminum is approximate the outer glass face has a slope on it to ly 13 x 1ùe inchedinch, lnsulallng sla" ¡ls" thermal mor,e provide water runoff. Caskets should Glas Unlt3 l¿-1' 31rc" V2' 1A ment of the curtain wall metal system be designed to give a uniform contact must be properly considered. Expan- pressure of fourto six pounds per inch sion at high temperatures and contrac- to make the seal watertight. Pressures figure 2. glazing dimensions

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setting blocks can be installed to within six inches of the vertical glass edge. The setting block should be 1/10 -'l inch in length for each square foot of glass area, but no less than four inches CLEARANCE BETWEEN in length. The setting block should be CLASS AND FRAME 1/16 inch less than the full channel TOLERANCES FOR width and be of sufficient he¡ght to SQUARENESS OF GLASS provide the nominal recommended WITHIN MANUFACTURING bite and minimum glass edge LIMITS clearance (Figure 2). BITE IN ACCORDANCÊ WITH MANUFACTURERS RECOMMENDATIONS Clearances, Shims, Drainage EDGE BLOCKS RECOMMENDED FOR Tolerances for the metal frame and DRY GLAZING SYSTEMS glass must be taken into account so that the glass is free to float in the '//) V//' ALLOW FOR DBAINAGE JAMBS opening and does not directly touch @ the framing system (Figure 3). Edge SETTING BLOCK blocking should be used to limit lateral 2 REOUIRED movement or side walking of the glass WEEP HOLES 3 _ 3/8'' DIA. caused by horizontal expansion or OR EOUIVALENT contraction and building vibration. Lack of edge blocking can permit glass to framing contact on one edge that could result in glass breakage. lf the glass is permitted to move to one side of the glazing channel, air and water infiltration can result. figure 3. clearances, shims, drainage Water should not be permitted to remain in the glazing rabbet. A weep system should incorporate enough temperature differentials caused by special performance required of the weep holes to ensure adequate various adjoining material, shading rest of the glazing components. drainage; usual ly this consists of three patterns and shading devices. lt must % in. diameter holes or equivalent, also have the ability to prevent water Considerations that may influence the equally spaced at the sill (Figure 2). penetration, prevent or minimize air choice of glazing systems include the infiltration or exfiltration, and create initial and replacement costs, and the thermal barriers to prevent heat loss workmanship available, since wet Glazing System through the frame and condensation systems requi re better workmanship. Performance Consideration on the frame. The location of the glazing joints may also have an influence. These are, The glazing system must have the At the same time, the system must also from least to most demanding: com- capability of transferring wind and im- present an appearance consistent with pletely interior, interior joint or ex- pact loads to the surrounding struc- design goals and retain its appearance terior light, protected interior and ture while cushioning the glass. lt and function over the anticipated life exposed exterior. must accommodate thermal expan- span of the building, given the sion and contraction of the frame and maintenance program planned. Final- The choice oÍ glazingsystem can also glazing materials and accommodate ly, the glazing system must match any be influenced by the glazing or

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preformed tape; ureather resistance under the bottom edge of the glass is less critical but adhesive and and spacer shims to ensure proper movement capabilities remain clearance between the face of the important. glazing material and the framing . Heel bead - applied on interior channels. side after glazing material is installed; provides a seal at removable stop; same considerations as those Common Causes of for toe beads. Glazing Failures

Solvent release butyls, acrylics and These are the most common causes acetic acid liberating silicones should of glazing failures: not be used when they come in con- ¡ Installation at temperatures tact w¡th insulating glass units, as the below 40 F. sealant may not be compatible with ¡ Failure to properly seal miter and the sealing material used for the in- butt joints. sulating glass units. The sealant sup ¡ Sash rabbet not clean and free plier and the glass supplier should be of contamination. contacted to determine specific com- ¡ patibi I ity recommendations. Lateral shifting or walking of glass. o Failure to properly bed, cushion lnstallation Considerations or center the glass. sealant materials used. Tinted and . lmproper glazing system used, reflective coated glass can heat Most sealants cannot be installed one that is not suited to the sash sealants to high temperatures. Reflec- below 40 F. Silicones can be applied design or building conditions. tive glass also increases intensity of at very low temperatures F) G20 with ¡ Setting blocks used incorrectly ultraviolet radiation on exterior cap proper precautions. Acrylics may re- or not at all. beads. Polysulfides, polyurethanes, quire warming if temperatures is . Frames surrounds of and silicones are generally well suited below 60 F. lf the sealant bead is in- or out for severe conditions; acrylics and stalled on a hot day, it will be in con- plane, improperly anchored buÇls can be used in less demanding stant tension during cold weather. lf and/or out of square. locations. Polysulfides, polyurethanes, installed on a cold day, the bead will . Lack of or improper positioning and silicones can withstand more be in constant compression during of spacers or edge blocks. joint movement than acrylic or butyl hot weather. ldeally, the sealant ¡ Damage to sash, rabbet or stops. based sealants. should be installed at a temperature o lncompatibility of sealants. about halfway between the extremes. The location of sealant bead in glaz- Tack free time affects the time trt]Ttr ing joint is also important: available for tooling and clean up. lf the new sealant bead must attain pro- . Cap bead - expected to provide perties quickly to withstand wind Excerpted from 'Architectural Glazing Prac- primary weather seal, therefore its loads or thermal movement, setting or tices" which appeared in the September 1985 adhesive strength, weather resis- full cure time will be important and issue of ASTM Standardization Nans, a publica- tion of the American Society for Testing and tance, and movement capability fast curing sealants should be Materials and usd with permission. Mr. Robett will be major properties to considered. G. Spindler is Director of Sales and Marketing consider; for Cadinal lG. . Toe bead - applied on exterior The basic concept in glazing systems side of channel before glazing to deal with the requirements cited is material is installed; provides a floating the glazing material within its secondary seal under cap bead or frame þ, means of setting block placed

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Glossary of Glazed Gurtann VMa[[ ]lernns

Acrylic - A group of water white thermoplastic resins formed by removable stop before fastening the stop in place. polymerizing the esters of the acrylic acid. Butyl - Synthetic rubber formed by the co-polymerization of Adhesion - The ability ofa coating or sealant to stick or bond to the isobutylene with isoprene. surface to which it is applied. Cap Bead - Bead of compound applied so as to have a slanted top Adhesive Failure - Failure ofa compound by pulling away from the surface that will drain water away from the glass or panel. (also surface with which it is in contact. called beveled bead) Angle Bead - A bead of compound whose cross section is triangular shaped with the hypotenuse side exposed. Also called fillet. Annealed Glass - Normal glass that is basically free of residual internal stresses so that it can freely cut. Annealed glass will fracture into jagged shards when broken. Annealing - A process ofslow cooling during curing which removes internal stress inherent in the material. Anodize - To coat aluminum with an oxide coating by electrolytic BITE action. May include dye materials as colorants. Backer - A material placed into a joint primarily to control the depth ofthe sealant. Bead - Sealant after application in ajoint irrespective ofthe method of application, such as caulking bead, glazing bead.

Ceramic Frit - A colored reflective coating fused to a glass panel BEDDING (usually spandrel panels) during the heat-treating process. Channel - A three-sided, U-shaped opening in sash or frame units in which the light or panel is retained by a removable stop. Contrasted with a rabbet which is an L-shaped opening. HEEL BEAD Channel Depth - The measurement from the bottom of the channel to the top of the stop, or measurement from the sight line to the base of the channel. Channel Glazing - The sealing of the joints around lighs or panels set in a U-shaped channel employing removable stops. Channel Width - The measurement between stationary stops (or stationary stop and removable stop) in a U-shaped channel. Cladding - Material used as skin of curtain wall. Bed or Bedding - The bead ofcompound applied between light of Clips - Wire spring devices used to hold glass in rabbeted sash without glass or panel and the stationary stop or sight bar ofthe sash or frame, stops, and face glazed. and usually the first bead of compound to be applied when setting Cohesive Failure - Splitting and opening ofa compound resulting glass or panels. from over-extension of the compound. Bent Glass - FIat glass that has been shaped while hot into a cylin- drical or other curved shape. Bite - Amount of overlap between the stop and the panel or light. Block - A small piece of lead, neoprene, or other suitable material used to position the glass in the frame. Bow and Warp - The departure from flatness normally inherent in CHANNEL DEPTH tempered glass from the manufacturing process. They are measured while the glass is resting on a flat surface with the concave side down. Break Fattern - The resultant geometric pattem formed by the cracks within an individual glass light when it is broken. (also called fracture pattern) Butt Joint Glazing - Method of installing glazing where the glazing is held at the head and sill by conventional methods, and the vertical edges are sealed with a silicone sealant. No vertical framing members are used between lights. Compatibility - The ability of two or more materials to exist in close Buttering - Application of putty or sealant to the flat surface of a and permanent association for an indefinite period with no adverse member before placing the member in position, such as buttering a effect of the one on the other. I

Compound - A formulation of ingredients, usually grouped as Insulating Glass Units - Multi-paned glass units consisting of two a vehicle or polymer, pigment, and fillers, to produce caulking or more panes of glass that enclose a hermetically sealed air space. compound, elastomeric joint sealant, glazing putty, etc. Interior Glazed - Glass set from the interior of the building. Compression - Pressure exerted on a material that tends to squeeze it. Curtain Wall - A non-bearing wall built between piers or columns that carries no structural loads except its own weight. Dry Glazing - Installing lighs using extruded rubber gaskets or closed cell sponge as one or both ofthe glazing seals. Durometer - A device used to measure hardness. Also a word used RABBET to describe the hardness of a material. FACE GI.AZING Exterior Flush Glazing - Glazing installed outside the structural SPACER SHIM frame of the building and attached on all four sides to the framing system by means of sealants. (also called structural glazing or s3opless CLIP glazing.) Exterior Glazæd - Glass set from the outside of the building. Exterior Stop - The removable molding or bead that holds the light or panel when it is on the exterior side of the light. SETTING BLOCK Face Glazing - On a rabbeted sash without stops, the triangular bead of compound applied with a glazing knife after bedding, setting and Interior Stop - The removable molding or bead that holds the light clippingt the light in place. in place, when it is on the inside of the light. Jamb - The two vertical members of a window or door sash. See also Reveal. Kink - An abrupt deviation from a flat plane or normal bow contour, most commonly found near an edge of a piece of tempered glass, A kink is always localized as compared with bow or warp. Knife Consistency - Compound formulated with a degree of FILLET hardness suitable for application with a glazing knife. I¿minated Glass - Ttvo or more plies of glass sandwiched with clear or tinted polyvinyl butyl, a plastic, between them. Lateral Shims - Material used to center the light laterally within the glazing rabbet. Light - Another term for a pane of glass used in a window or curtain wall.

HEAD Fillet - A bead of compound whose cross section is triangular with the hypotenuse side exposed. (also called angle.) Float Glass - Glass composed of silica sand and added alkaline salts made by floating a continuous stream of molten glass onto a bed of molten tin. trTont Putty - The putty forming a triangular fillet between the surface ofthe glass and the front edge ofthe rabbet. JAMB JAMB Gasket - Pre-formed shapes of rubber or rubberlike composition, used to fìll and seal ajoint or opening either alone or in conjunction with a supplemental application of a sealant. Glazing - The act of securing ofglass in prepared openings. Gun Consistency - Compound formulated in a degree of softness SILL suitable for application through the nozzle of a caulking gun. Head - The top of a window or door. Heat Strengthened Glass - Glass strengthened by subjecting anneal- Lock-Strip Gasket - A synthetic rubber gasket designed to engage ed glass to a special heat treating process. Not considered a safety the edge of glass or other sheet material in a surrounding frame glass because it fractures in the same patterns as regular annealed by forcing an interlocking filler strip into a pre-formed groove in glass. the face of the gasket. (also called zipper or structural gasket) Heat Tleated - Indicates that the glass has been treated to create Mastic - Heavy consistency compounds that may remain adhesive compression stresses in the surface. and pliable with age. Heel Bead - Compound applied at the base of channel, after setting Methacrylate Lacquer - A temporary protective coating applied the light or panel and before the removable stop is installed. One of to aluminum panels in the factory to protect against damage during its purposes is to prevent leakage past the stop. shipping. ¿

Mitred Joint - A 45 degree joint where horizontal members meet Sealant - Compound used to fill and seal a joint or opening, vertical members in a sash. usually by means of a caulking gun but may be pourable. Mullion - A vertical member that supPorts and holds two adjacent Setting - Placement of lights or panels in a sash or frame. Also, units of sash, glass, panels or sections of curtain wall. action of a compound as it becomes firmer after application. Muntin - Bars that divide the window into smaller lights of glass or holds panes of glass within a window, window wall or glazed door. Neoprene - A synthetic rubber having physical properties closely CAP BEAD resembling those of natural rubbe¡ but not requiring sulphur for vulcanization. Panel System - A type of curtain wall system that is similar to a unit system except that panels are homogeneous ståmped or cast SHIM metal, masonry, or concrete monoliths. Plate Glass - A high quality glass sheet of the same chemical SETTING BLOCK composition as sheet glass, but both faces are ground flat and parallel and then are polished. Polycarbonate - Plastic sheet used as glazing material, often in skylights. Polysulfide - A synthetic rubber used for sealing glazing joints. Folyurethane - A synthetic rubber used for sealing building joints. Setting Block - Small block used to distribute the weight of the glass or panel to the strong points of the sash, aid in the centering of glass or panel and to prevent glass to metal contact. Shading Patterns - Shadows thrown onto partial areas of installed glass which cause differential thermal stresses in the glass. Shim - Small blocks of composition, lead, neoprene, etc. placed under the bottom edge of a light or panel to prevent its settling down onto the rabbet or channel, thus distorting the sealant. MITRED JOINT Shore Hardness - Measure of flrrmness of a compound by means of a durometer hardness gauge. Sight Line - Imaginary line along the perimeter of lights or panels corresponding to the top edge of stationary or removable stops.

Pressure Wall - A wall assembly in which the units are all held in place through pressure applied by tightening bols or clamps with gaskes. SIGHT LINE l þrolytic Deposition - A method of coating glass by applying the metallic oxide to hot glass in a heat strengthening oven or float glass line. Rabbet - A two-sided, L-shaped recess in sash or frame to receive lights or panels. When no stop or molding is added, such rabbets are face glazed. Addition of a removable stop creates a channel. Racking - Movement or distortion of sash or frames due to lack of rigidity. Rainscreen - Waterproofing system that works by negating the water driving force of wind by equalizing air pressure on either side of Silicone - A synthetic rubber used in sealing glazing joints and joints. adhering exterior flush glazed panels and lights. Rellective Glass - Clear or tinted glass coated with an extremely Sill - A horizontal closure at the bottom ofa glazed unit or assembly. thin layer of metal or metallic oxide causing it to reflect Sloped Glazing - Any glazing installed 15 degrees or more from a significant amount of the light and heat whicb strikes it. the vertical. Reveal - The side of an opening in a wall for a window or door. Spacers - Small blocks placed on each side oflighs or panels to Safety Glass - Glass so constructed, treated or combined with other center them in the channel and maintain uniform width of sealant materials as to reduce the likelihood of injuries to people when the beads. glass cracks or breaks. Spandrel - The panel of a curtain wall bétween adjacent structural Sash - The framework which holds the glass in a window or door. columns and between the window sill and the window head below Screwon Bead or Stop - Stop, molding or bead fastened by machine it. Spandrels are usually used to obscure the floor line. screws as compared to those that snap into position without Spandrel-and-Column-Cover - Custom designed curtain wall additional fastening. systems where column cover panels are attached directly to the I

structural columns and spandrel panels connected to the floor slab, Ultraviolet - Short wave length light outside the visible spectrum at spanning the distance between columns. the violet end. Spandrel Glass - Heat strengthened or tempered glass with a Unit - Term normally used to refer to one single light of insulating ceramic frit color permanently fused to the interior surface. Not glass. a vision light. Unit System - Tlpe ofcurtain wall system that are prefabricated, shop Spline - A thin strip locking two panels together by being inserted assembled, one story or multi-story units designed to interlock into a groove cut into the end of each panel. vertically and horizontally. Usually shop glazed. Squareness - Measurement of the accuracy of the glass dimensions. United Inches - Total of one width plus one height in inches. Unitized Stick System - Tlpe of curtain wall system that consists of CHANNEL prefabricated vertical mullions and interlocking horizontal members that function like a unit system after installation. Vacuum lleposition - A method ofcoating glass by means ofvacuum REMOVABLE STOP chambers and electrical energy. Vent - Provide circulation of air between two partitions. Weatherstripping - A thin strip of material used to cover the joint between the sash and thejamb, casing or sill to keep out rain, air, dust, etc. Wedge - An extruded resilient dry glazing component shaped so as to develop a sloped, finished top. STATIONARY SÍOP

Stationary Stop - The permanent stop or lip ofa rabbet on the side away from the side on which lights or panels are set. Stick System - Tlpe ofcurtain wall system made up ofvertical and horizontal members that assemble in place on the building. Stile - One of the upright structural members of a frame. Stop - The stationary lip on the back of a rabbet or the removable molding at the front of the rabbet, either or both serving to hold light or panel in sash or frame.

WEEPHOLE

sroP SECTION THROUGH PI.AN VIEW HORIZONTAL MEMBER

Weep - A small opening in a wall or window to drain water to the exterior. Wet Chemical Deposition - A method of coating glass by precipitating metal from a chemical solution by means of a reagent. Wet Glazing - Insølling lights by use of preformed tape, gunnable Tempered Glass - Glass strengthened by subjecting annealed glass sealants, putty or glazing compounds. to a special heat treating process that prestresses the glass making I{ired Glass - Glass that has a welded wire netting introduced into it four times stronger than normal annealed glass. TÞmpered glass molten glass just before rolling. will f¡acture into small pebble size fragments with rounded edges. Thermal Break - A gasket system that separates the outside and inside metal surfaces to reduce the heat flow by conductance through the metal. finted Glass - Glass made by adding various colorants to the normal clear glass batch. The color reduces the solar transmittance Glossary is publishd by Hoffmann Architects, specialists in in- of the glass by frlæring out part of the color spectrum , cuts down glare, vest¡gative and rchabi litatitrc arch¡tecturdengineering. Our offìce and may be used to control ultraviolet radiation and increase heat is locatd at 432 Washington Avenue, North Haven, CI 06473, abso¡ption. Phone (203) 239-6660. Tlrc Bead - Compound applied at the base of a channel before setting the panel or light, its purpose being a secondary seal to prevent leakage past the exterior stop. f c selvtces

Representative Projects

Specialists in the solution of roofing, ment Corporation, Hoffmann Ar- masonry curtain wall and structural chitects prepared construct¡on Journal i s a publ icati on of Hoffman n problems, Hoffmann Architects documents and administered the con- Architects, specialists in in- recently completed work on the struction contracts for curtain wall vestigative and rehabilitative ar- fol lowing representative projects. rehabilitation at the Warner Com- ch itecture/engi neeri ng, i ncl ud i ng munications and Eastern Airlines the analysis and solution of roofing, Curtain Wall and Facade buildings. exterior wall, glazing and structural The firm prepared construction problems. documents and will assist in the bid- Another Rockefeller Center project We welcome contributions to HNJ ding process for roof and masonry involves rehabilitation of the from our clients and friends. Please restoration at the Prentice-Hall limestone facade of the Exxon send news, technical information, Building in Englewood Cliffs, New Building. Hoffmann Architects com- address changes or requests for free Jersey. pleted construction documents and subscriptions to Ann Prokop, will administer the construction con- Hoffmann ArchitectlJournal at 432 The Durst Organization, a New York tract for repair of the stonework, Washington Avenue, North Haven, City real estate owner, retained Hoff- resealing of the joints and cleaning of Connecticut 06473. mann Architects to survey the condi- the limestone. The building is owned tion of the windows, masonry and by Mitsui Fudosan (New York) lnc. W h i I e H offman n A rch i tectlJ ou rn al attempts to provide the ac- curtain wall of the Random House most curate information on general sub- Building at 825 Third Avenue in Hoffmann Architects is preparing con- jects, it is not intended to be a Manhattan. struction documents and administer- substitute for professional arch itec- ing the contract for an exterior tural and engineering services. We For the Rockefeller Center Manage rehabilitation project involving re. strongly urge you to consult a pointing, sealing, painting and win- qualified rehabilitative architec- dow repair of a Southern New tural/engineering firm (ours) for England Telephone facility in New answers to specific questions. For Haven, Connecticut. more information on the seruices we offeç please call Brian Schafer at (20Ð Roofing 239-6660. For the Schering-Plough Corporation, Hoffmann Architects surveyed the roofs of 5 buildings in Bloomfield, New Jersey.

ln White Plains, New York, the firm surveyed the condition of the roof of a General Foods Corporation facility.

For Union Carbide Corporation, Hoffmann Architects sunq,ed the roof and is preparing construction docu ments for a facility in Moorestown, New Jersey. 825 lhird Avenue in Manhattan f

Precautions in SpecityinS Glass

By Donald Vild, PE

Low emittance (Low-E) coatings offer The coating is applied to one of the a Lor¡¡-E coating is primarily a residen- major improvements in the thermal air space surfaces of the glass and tial product. lt is furnished on clear performance of insulating glass units. reduces the heat transfer by radiation glass only, except in rare cases. The But there is a potential pitfall that is across the air space of the insulating coating does little to reduce solar heat often overlooked. glass unit. Thermally, the result is gain the main concern in commer- similar to inserting a blanket of fiber cial buildings.- Low emittance coatings for glass have glass in the air space. The outboard been available for 40 years or more. glass is closer to outdoor air Regardless, its use is increasing in Unfortunately, they tended to have temperature and the inboard glass commercial buildings, principally in distinct, unpleasant colors by reflec- closer to room temperature. conjunction with reflective and heat tion, often with severe variations. absorbing glasses. This is where the \Mthin the past decade, improrcments Nominally, a double (two panel) in- problem starts. The effect of the ) harre been made in the aesthetic quali- sulating glass unit with a Low-E coating on glass thermal stresses is ty of the coatings. The color is subtle, coating will have the same insulating ignored. often unnoticed, and uniform. This value as a triple (three pane unit) has caused a rapid growth in the use without a Low-E coating. Equal in- Based on analysis and practical field of Low-E coatings in insulating glass sulating value is achieved at a markd- experience, certain types of high per- units. ly reduced cost. lnsulating glass with formance insulating glass units have most often been furnished with both panes of annealed glass. Typical are units with gray, green, or bronze tinted heat absorbing glass as the outboard pane. The maximum edge thermal stress for these types of glass in a wall with no major exterior shading is roughly 2050 psi. Breakage would not be expected. The stress might increase to 2400 to 27OO psi when there is shading from vertical or horizontal projections. At these levels, breakage would be minimized if the glass cut- ting is proper and the edges are not seriously damaged. Field experience has supported this.

The pitfall

However, when a Low-E coating is in- cluded, the outboard sunlit glass will reach a higher maximum temperature

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d technical notes

than without the coating, all other things being equal. This increases the edge thermal stresses and the potential for thermal stress breakage.

For insulating glass units with heat aþ sorbing glass, the stress increases to roughly 2400 psi for a flush wall and to a range of 2800 to3200 for a wall with shading from projections. This assumes that the coating adds no ab. sorptance to the glass. For most types of Low-E coatings, their absorptance will add 200 to 300 psi to the stresses.

It is generally agreed that an edge thermal stress of 3000 psi is the up per working limit for annealed glass. Two basic precautions to follow: analysis be furnished by the glass Above this value, thermal breakage is manufacturer or fabricator. Be cer- possible. lf thermal breakage is to be a. Do not assume that glass products tain that the analysis addresses the prerrented, annealed glass may have to that have historically been fur- shading patterns that may occur be heat-strengthened when a Low-E nished with annealed glass will on the building. lnln coating is applied. Examples for many not be affected by a Low-E reflective coated glasses used in com- coating. Reprintd from EXTERIORS magazine, Wnter bination with a Low-E coating lead to 1988. Used with permission. Donald Vild, PE the same conclusion. b. Require that a thermal stress is with Donald J. Vild Associates, Orcgon, Ohio.

W¡ndow Standards Alert

ln 1985, the American Architectural the specifier to select windows that Wind Velocity Pressure. ln some com- Man ufaturers Association (AAMA) i n- will not have an objectionable amount binations of wind speed and height, troduced a voluntary standard for of condensation based on outside this may require changing the window aluminum prime windows. ln 1988, temperature and indoor relative specification to the next highest Pefor- AAMA updated those standards and as humidity factors, also replacing Roman mance Class designation compared to of June 30, 1989, all certification tests numeral desi gnations. A specification the old standard. Several Area Factors will be to those standards. for "Dual Action" windows has been in the Class Table have been increas- added. Dual Action windows are those ed. Area factors are factors by which Thermal transm ittance and condensa- that may be opened two different ways the tabulated maximum glass area may tion resistance have been added, but at the user's option. be multiplied to take into accountthe are optional. "U-Value Classes,, have strength of various types of glass. replaced the Roman numeral designa- ,,-Rf Wind load tables have also been revis- tions formerly used by AAMA. ed to reflect an upgrading of Design Classes" have been added to enable Pressure from 1.-l to 1.25 times the f

d staff news

Staff News Glazing o o =ò=N Ð r= m lo (t, ge Surfaces U' o=' c) _r (ã B. Beaudry and Frank B. o fane Scherr, Ð o-o9 associate members of AlA, are par- ft r> m oot< ticipating in the National Council of Which glass surface in an insulating o of glass I oo Architectural Registration Board's unit is considered the No. 1? For oz c architectural glass materials, the glass Ð o (NCARB) lntern Development m o surfaces are counted from Program. the outside co o{ in. Therefore, the No. 1 suÉace istothe m Ø exterior of the building. This becomes -l Brian W. Schafer has been appointed am extremely i mportant when specifyi ng to the Membership Development Task coated glass for multiple glazing Force of BOMA New York. ap plications, since where the coating is located affects its usefulness. Richard P. Kadlubowski and lane B. Beaudry recently completed CADD training for the firm's new CADVANCE computer aided design and drafting dfr'ßt* lJføru4 system.

Hoffmann Architects is pleased to announce the addition of three ns,v staff memben. They are Ernest E. Swanbery AlA, who joins us as senior architect, Scott D. Chamberlain, drafter/project ?- 9 4 representatiw, and Malik M. Nawaz, also d rafter/project representatir¡e. 4vÆ)4 *

We've Moved!

Hoffmann Architects is pleased to announce its move to new offices at 432 Washington Avenue, North Harren, Connecticut O6473.Our new phone is (203) 239-6660.