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<ept inside, ÏOur', building envelope is a blend while smoke is allowed to escape of complex technologies that can be through vents. The envelope acts as a barrier to: used with resourcefulness and subtlety . to achieve important benefts for the Raìn, snow, hail, wind, and humidity . Dirt, soot, pollen, dust, and debris owner and the user. The medieval . mason did a fìne job with sand-lime lnsects, spiders, and animals . Noise mortar and local stone, but today's . built environments offer a much Fire . Ultraviolet light greater potential for comfort and . effciency. The risks, however, are also Unauthorized people. greater: poor design, careless installa- tion, and neglected maintenance will The Sources of Building Decay quiclcly undermine the value, purpose, Nothing, of course, lasts forever, and and benefts of the modern building buildings are as subjectto decay and envelope, deterioration as all else. The enemy is water, along with the effects of thermal Owners and facility managers can best expansion and contractìon. While protect their building investment by these forces of nature are constant and understanding the potential of the cannot be eliminated, their effects can building envelope and its risk of be mitigated and protected against. deterioration. To do so requires an The weapon of choice? A well understanding of each building enve- designed, well constructed, and well lope component and its inherent maintained buildìng envelope. strengths and weaknesses, Unfoft unately, the primary contributing 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<s at lodged glazing gasl<ets, deterioration of described above, the damaging effects these components, their potential for mortar joints, or improper installation of thermal action are resolved by using decay, and some common causes of of f ashing membranes. a f exible joint of suffìcient width which deterioration, consists of a pre-compressed joint f ller, What all these can lead to is damage backer rod, and high-per-formance Curtain Walls from water infì[raÏon and thermal sealant. This conlruction allows the A curtain wall is an exterior building action, Waten worl<s its way into a window to comfortably expand and wail that carr¡es no vertical loads, building through any one of six natural contract within the masonry wall while commonly known as a non-load sources: gravity, kinetic energy, surface preserving the weatherproof facade. bearing wall. While there are many tension, capillary action, and air variations in curtain wall construction, currents and pressure drops. Any of Example A below shows the varying these wall types typically fall into fìve these, singly or in combination, can rates of expansion for commonly used categories: metal curtain wall, masonry tal<e theirtoll overtime. A poorly building materials, and underscores the veneer, exterior insulation lnish system designed or maintained building is importance of factoring in these (EIFS) stucco, and wall panels, Metal simply one that's all the more ready for expansion rates when designing a new curtain walls and masonry veneer are problems and one that will begin to facility the most common, and are explored in decay all that much sooner. more detail below. 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<s and openings in the Stainless Steel .00099 common term for a metal cuftain wall building envelope, paving the way for installed between floors, or between future diffìculties. Steel .00065 the foor and roof 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<s which must be guarded against the veneer and the back-up wall, ofthese spaces. both during initial design and in ongoing 3, Pre-assembled into panels and 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 .