Hotfmann Architects
Journal of architectural technology published by Hoffmann Architects, specialists in eñedor rehabilitation
First Issue I995 Volume l3 Number I
A Primer on Deterioration in Building Envelopes
through, while preventing others from John f. Hoffmann, FAIA enterìng or exiting, as the case may be, For example, cooled air is l The building envelope as a whole is factors to premature building deterìora- tion events which open the best defìned as a f lter between the -those interior and exterior environments, floodgates, as it were - are those allowing some elements to freely pass caused by lhe humon element desìgn lnvestigation of leaks in a bronze-and-glass defciencies, poor material selection, curtain wall on a New York City building. improper construcLion, deferred lohn l, Hoffnonn, FAIA is principol of maintenance, applied forces, weight, Hoffmonn Architects, cnd ls responslb/e vibrations, pollutìon, and vandalism. for oll the flrm's octivities in the restoro- tion ond renovation of building enve/opes. ln general, building envelope problems He is o notionolly recognized exÞeft on are usually caused by the failure of the ccuses ofond solutionsfor building glazing compounds or sealants, corro- d ete rt o roti o n p ro bl e ms, sion of steel supports, clogged weep Copyright Hofmann Architects 1995 Hoffmann Architects / Journal holes, loss of sealant adhesion, dis- ln the case of the aluminum window maintenance, The following lool Thermal movement does not cause CoeffÌcient of Linear Metal curtain walls damage in and of itself The problems Expansion for 100' F These walls consist principally of metal, arise from the varying rates at which or a combination of metal, glass, and different building materials expand and other surface materials that are contract, The pressures caused by Aluminum .00 t28 supported by or within a metal these incompatible actions are what framework, "Window wall" is a lead to cracl 2 Volume l3 Number I 4 is caused by: Flashing membranes and weep tubes . Excessive moifure penetration at must also be incorporated, joints. . Successive freeze-thaw cycles. 2. Metal curtain walls typically suffer . Exposure to weather and pollution. from glozing fciiure, often caused bythe . Uneven settlement of building following design and construction foundation. errors: . Thermal movement of masonry. . Failure to properly seal miter and . Unequal expansion and contraction butt joints. between the face masonry and its . A dirty or contaminated sash rabbet, bacl<-up wall or structural support, . Lateral shifting or "walking" of glass, . Failure to properly bed, cushion, or The following illustrates the damage centerthe glass. potential of decaying mortar: Within . lmproper glazing system that is one square foot of brick wall, there are incompatible with the sash design or I 3 lineal feet of mortar-and-bricl< building conditions. A rather poorly constructed masonry wall surface. lf each brick-to.joint interface . lncorrect use of or failure to use Note the many openings in the mortar, develops a hairline crack of only I164", setting blocks. which allow water entry. the net effect on the building s water- proof ng rntegrity would be equal to a attached to the structural frame. l/4" x 8" opening ample room for 4, Anchored to a back-up wall of steel plenty of waterto get in. studs and gypsum sheathing, Deteriorated mortar joints can be The most common type of masonry repaired by repoínting, tuck pointing, ond curtain wall is defìned as a masonry Þo¡nting, These are methods of cavity wdl that consists of masonry removing and replacing old mortar with veneer on Lhe exlerior, an inner air new mortar. This complex, labor- space, and a back-up wall, Relieving intensive, and costly process is, angles at each spandrel beam or foor nevertheless, essential to preventing slab are used to support the weight of water entry and furlher building the masonry, making the masonry wall deterioratìon. a true non-load bearing curtain wdl, The brick has lost its face from water Another problem facing masonry wdls entering the wall through the back of the Curtain wdl problems is woter inftltrotion at the relieving angle ParàPet. Weal< links in the waterproof ng system that supports the weight of the are often found in curtain walls and masonry. This is usually caused by a . Out-of-plane, out-of-square, or masonry, pafticularly at intersections or failure to leave adequate room for improperly anchored window frames or joints where the roof meets the expansion under the relieving angle. surrounds. parapet, ln addition, each type of Thermal movement between the bricl< . Lack of or improper positioning of cudain wall faces its own common and the steel relieving angle will spacers or edge blocks. construction or design defects, which ultimately force the brick to bulge out . Damage to sash, rabbets, or stops. are described in more detail below: and pull away from the structural . Damage to glass edges, eventually support, The solution either during leading to large cracks, l. Masonry curtain walls: A major original design on as a major- repair . Incompatible sealants. problem in masonry curtain is the is walls effort - to re-set the bricks and deteriorotion of mortor joints (the hori- install a proper soft joint, A soft joint Joints and Sealants zontal and vertical bands of mortar consists of sealant and a backer rod set The joint is where two parts of the between bricks in a bricl< facade), which in front of the angle and empty space building strusture meet and must be Ieads to water entry. This deterioration or compressible lller unden the angle, held together. As with all else in the 3 Hoffmann Architects / Journal ¿ the movement may be cumulative and impossible to predict ln those cases, the sealant choice should be one with high movement capabilityto ensure maximum safety. Polysulfde and polyurethane sealants are recom- mended for movement rates between + 175% and t 25%, Silicone sealants are highly resistantto weathering and provide excellent flexibility and resilience for movement rates as high as + 50%, The latter would be the only choice for a butt joint with a joint width of l/8" and an expected move- ment of + l/ I 6", This completely deteriorated copper counterflashing was not replaced when the wall was re-pointed, a poor effort in itself. buildìng envelope, joint integrity is vital polyurethanes, silicones, acrylics, acrylic to building longevity and must be well latexes, butyls, and oil-based caulks, constructed and regulady maintained. For major expansion joints, a heavy- Joints must be both flexible and duty compressible material called a watertight, Use of proper sealants and compression seal can be used to correct joint size is a critical factor in accommodate building movement, every sealing situation where building Each chemical ingredient used in movement will occur. The size of the sealants has unique properties that joint is defìned as the distance from must be thoroughly investigated with one substrate to another, with joint the sealant manufacturerto ensure movement expressed as a percentage proper selection for specifìc building Adhesive failure of the sealant at the joint distance, conditions. of this connecting the brick masonry, wall flashing, and aluminum window. Temperature changes have the most One-part moisture-cured silicone and impact on joints and their sealants, polyurethane are the most commonly Cold tends to sliffen most sealants, used sealants for building envelope Sealant ioint problems reducing both their resiliency and their joints. Relatively new to the sealant lYost sealant joint failure is caused by ability to absorb the stress caused by industry, silicone worl 4 - Volume l3 Number I ¿ solved before re-sealing. lf no cause weathering, solar rad iation, water can be determined, start from scratch ponding, freeze-thaw cyclìng, flow-off by feld-testing the various cleaning and alligatoring, or damage from foot traffìc, priming combinations with the selected falling objects, and temporary place- sealant until the right mix is found. ment of equipment or tools. . Through trapping of moist air Coheslve foilure is the failure of the between plies of felts due to incom- sealant to bond to itself as evidenced plete coatings of bitumen or embed- by crack and splits in the center of the ment of felt into bitumen, Blistering applied sealant. This type of problem is occurs when moisture is trapped clear evidence that the joint's move- between orwithin the plies of felt or ment was more than the sealant could under the membrane itsell handle. . Through flsh mouths or edge wdnkes in felts where they overlap Cohesive failure of the sealant in a brick Roofing otherfelts, a problem caused by masonry expansion joint. Roof assemblies are made up of two improper membrane instal lation, principal elements: the substr¿te (framing, decl<, and insulation) and a synthetic rubber, plastic, or modifed Premature roof ng failure may also be continuous membrane barrier used to bitumen, due to: protect the substrate from water entry, . Splitting due to tensile stress (resis- Roofing problems tance depends on the strength ofthe These continuous roofìng membranes Premature failure of roolng mem- membrane and the fastening method). fall into three categories: branes is more often a problem of . Slippage due to inadequate anchor- . Buìlt-up membranes: successive layers incorrecl design decisions and im- age; using bitumen with too low of a of bitumen and felt, often with a gravel proper material installation, rather than softening point; high roof surlace or mineral granule surface, that of defects in the matedd itself temperatures; or the excessive coating . Liquid-applied membranes: sprayed or ÌYoisture damage, the leading cause of of bitumen between plies of layering or rol led-on elastomeric coatings, roof decay, usually appears fìrst as aggregate sur[acing, . Single-ply membranesi sheets of wdnlies, blisters, or ridges that show . Uplift resulting from air movement at up long before any actual leal \I felts or insulation before installation. decay. Unless those causes are found . Through migration of watervapor and fìxed, any repair effort will be ü through open joints or cracl 5 Hoffmann Architects / Journal on-site representation to monitor the The Facility Manager's Bookshelf: The Building Envelope repair work, Given the extent and expense ofthe average repair project, it A. Basic References is well worth the cost of the professional fees to make sure the job is done L AAMA Technicol Reþrence Center $450,00 correctly the fìrst time, Patching and Volume I: Windows ond Sliding G/css Doors Volume 2: Metol Cuttoin Wolls re-doing poor rehabilitation worl< is an Volume 3: Aluminum Storefront ond Entronce Monual endless cycle that only gets more Volume 4: Skylight ond Spcce Enclosures expensive over time, To orden The American Architectural lYanufacturers Association (AA|\4A) (708) 202-r 3s0 One reason owners and managers often 2. ASD Manuol of Steel Construction, 9th Edítion. $72.00 run into difficulties in solving building To order: American lnstitute of Steel Construction, Inc (AISC), decay problems is that they immediately (312) 6t0-7400. turn to a specifìc contractor who 3 B/A Technicol Notes. $75,00 specializes in the building area that's To order: Brick Institute of America (BlA), (703) 620 00 l0 leaking, For example, if the roof leal (2 | s) 29e-ssBs. Where To Start There are no simple answers to water C. Construction Specifìcations Institute infìltration and building deterioration | , Beall, Christine, "Selecting and Specifing Caulking and Sealants," problems. ln older buildings, the prob- The Construction Specifler. Yiarch 1990, p, 54. lems most often result from age or neg- 2 Dworkin, Joseph F, "Evaluating Roofs Using Non-Destructive Methods," lect, or some alteration to the water- The Constructton Specifter. November 1990, p.82. "The proofìng system, ln newer buildings, the 3. Grimm, Claylord, T, Hidden Flashing Fiasco." Ihe Construction Specifier. 1994, p. 134. problems arise most often from poor )une 4, Quirouette, Rick, "Rain Penetration Control." The Construction Specifler. design, poor construction, poor materi- November 1994, p.48. als, or some combination of these, 5. Raeber, John A, "Roofìng and Waterproofìng Pre-lnstallation Conferences: Wishful Thinking?" The Constructton Specifier. November 1989, p. 3l repair a Any effort should begin with 6. Rogers, Tyler Stewart. "ls lt A Leak, Or ls lt Condensation?" The Construction review of the original plans and specifìca- Specifier. September 19 66, p. 26. tions, and a physical inspection of both To order: $4 each from Speclfer Repdnt5 60 | lYadison Street, Alexandria, the building's interior and exterior. This Virginia 223 I 4- 179 i (800) 689 -2900 can help determine whether system D. Past issues of Hoffmann Architects'JOURNAL failure was due to age, poor materials, Accurso, Dominick,Jr, AIA and Alan P. Eddy, CDT. "The Care and or faulty design and installation, L Preservation of SealantJoints," Volume 12, Number2, 1994. 2. Sanders, Arthur L. "Solving Glazed Brick Deterioration Problems." A building envelope is a complex sys- Volume I l, Number 1,1993. tem of interacting components, with 3. Kadlubowski, Richard P, "Avoiding Added Wear and Tearto Roofìng." ample opportunity for things to go Volume 10, Number 7, 1992. wrong. Expert preparation and execu- To order a complimentary .opyt call Brian W, Schafer or Emily D, Dowden at tion of the construction contract will Hoffmann Architects, (203) 739 -6660. help keep the repair project on track. I Compiled by Alan P Eddy Technical Information Specialist I 6 Volume l3 Numben I 4 R E P R E S E NTAT tV E P R O t E CT S Building Envelope Rehabilitation Hoffmann Architects specializes in the Hoffmann Architects has provided Southern Connecticut State rehabilitation of existing facilities, A building envelope rehabilitation University primary focus of the fìrm's work is on seryices to numerous corporate and Buley Library the diagnosis and resolution of building institutional clients. Among these are New Haven, Connecticut envelope problems, from roof leak to the following: (State of Connecticut DPW) curtain wall deterioration to founda- tion decay. North Point Office Complex New London C.O. # 2 Cleveland, Ohio New London, Connecticut In helping clients resolve these (North Point lYanagement/The (sNEr) problems, Hoffmann Architects Equitable) investigates existi ng conditions, Borough Hall prepares construction documents to Trinity College Staten lsland, New York guide the work, and administers the Vadous buildings (New York City, Department of construction contracts for all renova- Hartford, Connecticut General Services) tion and restoration services. (Trìnity College) Rocl The Kyesongwon Training and Education Center in Chonan, Homer D. Babbidge Library, University of Connecticut at Storrs. Korea. 7 'l Hoffmann Architects / Journal ¿ 1 o \Jar¡ Waterproofing v {^r I ÞË { v=< '- ct+ ÚIP J-a I S lt \o Þ a]- T P U o\O l Z õlûq dP C) OOY o= o: tt, Z ))> Ï" n.rt step in mal Edltor Emily D. Dowden Crophic Services: Bligh Graphics Edito riol Services: Jonel le Lawhorn H obbs Commu n ications Iroof This wall type is usually composed of vertical and For example, an aluminum window Concrete .00055 horizontal framing members (mullions) frame set in a masonry wall can expand that contain fxed vision lights and at twice the rate of masonry. This can Glass .00050 opaque spandrel panels. The mullions lead to failure of improperly designed hold the glass vision lights (glass or installed sealant joints, ultimately Marble .00045 windows) and spandrel panels in place, creating openings for water entry. and give the metal curtain wall ìts Limestone .00042 characteristic appearance of a rectangu- While most thermal action is caused by lar grid, The spandrel panels are the seasonal temperature changes, even Brick Masonry .00034 opaque panels that conceal the foors, localized variations in expansion and ceilings, and mechanical spaces. contraction can occur from something as simple as shading from direct sun. Example A: Building envelope failure can Masonry veneer A well designed building is able to often be traced directly to a failure to plan Masonry exterior facings, called veneers, accommodate these dimensional for differing rates of movement among can be installed using any one of four various building materials. changes through the use of carefully construction methods: calculated joint tolerances and flexible l. Attached directly to a masonry sealing methods. Joint tolerances are Building Envelope Components bacl<-up wall with masonry ties or the open spaces between various Each building envelope component has modar. structural components, while flexible its own inherent risks for deterioration, 2. Construcled with a cavity between sealing methods help keep water out risl