Accommodating Movement in Building Envelope Materials

I S S U E 4/2017  VOLUME 34  NUMBER 4

Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Accommodating Movement in Building Envelope Materials

Richard P. Kadlubowski, AIA and Christopher M. DeRosa, AIA, PE

W e may think of the building are anticipated, the design should ac- envelope as an inanimate object, but, commodate each material’s propensity really, its components can be quite for expansion and contraction, and the mobile. Building materials grow, shrink, building enclosure must allow for dif- shift, bulge, deform, and elongate in fering – and, often, opposing – move- response to stresses and fluctuations ment of adjoining materials. in the environment, and these dimen- Calculations and detailing for seem- sional changes often impose strain on ingly small movements in the building adjacent elements. envelope may seem cumbersome and Where the forces of movement are time-consuming, however the forces not foreseen during design and con- that develop from these deformations struction, evidence of the struggle will can be immense. Neglecting to include emerge, in the form of cracks, spalls, adequate expansion joints, control displacement, broken glass, warped joints, bond breaks, flexible anchorage, metal, and, eventually, breakdown of slip planes, and other means to allow the assembly. for changes in dimension will ultimate- Failure to anticipate and allow for ly expend more time and money in movement in building materials com- remediation than a prudent approach pels imparted stresses to find their would require at the outset. Where own path to release, which is nearly al- a building owner is faced with the ways an undesirable one. Not only are unfortunate discovery that such prac- cracks unsightly, they also open path- tices were not employed at the time ways for moisture penetration into the of construction, all is not lost. There building enclosure, which compounds are rehabilitative measures that can be the problem as materials swell or cor- taken after the fact, but unless the un- If expansion joints are not provided, the rode, placing further outward pressure derlying issue of restrained movement building will make its own. on adjoining components. is addressed, cosmetic fixes to cracked masonry or displaced stone will do To design for movement in the build- little to keep ahead of the problem. ing envelope is to identify the properties of the materials used in construc- With attention to the causes of tion, as well as the environmental and movement, including fluctuations in siting conditions of the building, and to ambient temperature and moisture, develop a design that either minimizes applied loads, chemical interactions, or allows for such movement. For and materials’ propensity to expand or instance, where dimensional changes shrink over time, the general behavior

Richard P. Kadlubowski, AIA, Senior Vice President and Director, Architecture, manages Hoffmann Architects’ Virginia office, where he diagnoses and treats distress in building enclosures. Christopher M. DeRosa, AIA, PE, Project Architect, brings both architecture and structural engineering to the challenges of building movement. JOURNAL

of each element in relation to others to 100°F, for which the panel would From then on, it expands as it absorbs can be predicted. To allow for factors increase in length 0.0000098 in./in./°F moisture from the atmosphere and that might impact as-built conditions, a x 120 in. x 100°F, which is 0.1176 in., precipitation. Drying the brick at nor- conservative approach to incorporat- or just under 1/8 in. Although this mal temperatures will not reverse this ing fluidity in the building envelope de- number might seem small enough to expansion process, which is greatest sign should limit movement if possible be negligible, restraining the copper in the first few weeks after firing but and accommodate material move- sheet by hard fastening it at both ends continues at a slower rate for years. ment, without imposing restraint. would lead to bowing and buckling as Just how much a given brick will ex- the temperature rises and the cop- pand depends mainly on raw materi- Types of Movement per expands, and, as the temperature als, but firing temperature is also a When designing for movement of drops, the shrinking metal would strain factor. A brick fired at lower tempera- building enclosure materials, architects at the fastening points, potentially tear- tures will expand more than the same and engineers must consider dimen- ing itself apart. brick fired at higher temperatures. sional changes that can Concrete shrinks as it cures, COEFFICIENTS OF LINEAR THERMAL EXPANSION arise from the effects of the due to the natural moisture environment, including tem- MATERIAL AVERAGE COEFFICIENT loss that occurs soon after the perature and moisture varia- OF LINEAR EXPANSION concrete is cast. As with brick, (x10-6 IN./IN./°F) tions, as well as elastic and the initial dimensional change inelastic deformation from BRICK 4.0 of concrete is irreversible and applied loads and volume CONCRETE (STRUCTURAL) 5.5 tends to be significantly greater changes due to chemical in- CONCRETE (NORMAL POURED) 8.0 than any ensuing moisture- teraction. Designers should related volume fluctuations. also take into account the STAINLESS STEEL 5.5 TO 9.6 The degree to which con- tendency of a given material TYPICAL STEEL 7.3 crete will shrink during curing to shrink or expand over its COPPER 9.8 depends on the properties service life, and the ways in ALUMINUM 12.8 of the concrete mix, including which neighboring materi- GLASS (PLATE) 5.0 water-cement ratio, cement als with opposing volume composition, and aggregate changes might pull or push GLASS (HARDENED) 3.3 type, as well as size of the con- against each other. crete unit, curing conditions, and size Temperature Movement Moisture Movement and placement of embedded reinforc- Changes in temperature cause most Porous building materials such as brick ing steel. building materials to expand and and concrete expand as they absorb Wood is the building material most contract. Unless the movement is water and contract as they dry. Like subject to dimensional changes due to restrained, the changes are generally temperature movement, moisture moisture. As part of the commercial reversible. As the temperature rises, deformation is generally reversible, seasoning process, the wood shrinks materials tend to expand, then con- except in the case of the initial shrink- as moisture content diminishes from tract again as the temperature drops. age or expansion that takes place the initial fiber saturation point, until How great these volume changes are with some building materials. Often reaching equilibrium with the environ- depends on the type of material and considerably greater than subsequent ment. After this initial shrinkage, chang- may be expressed in terms of coeffi- reversible moisture-related dimension ing moisture content in the wood will cient of thermal expansion (see table). changes, expansion or contraction due continue to cause the wood to swell Projected thermal movement is the to natural aging can yield significant and shrink. The degree of shrinkage product of the coefficient of thermal internal stresses that may manifest as differs in the radial, tangential, and expansion, the overall temperature cracks, spalls, open joints, and leaks as longitudinal directions, with the latter change, and the length of the compo- restrained elements struggle to release typically so small as to be considered nent. As an example, take a 10-foot built-up pressure. negligible from a design standpoint. sheet of copper roofing at a building Brick is smallest in size after exiting the This swelling and shrinkage can ulti- site with a temperature swing of up kiln, when it is the driest it will ever be. mately cause the lumber to crack.

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Chemical Action In the presence of moisture, chemical reactions can take place within or between building materials that impact the volume and integrity of the component. Corrosion occurs when ferrous metals are exposed to moisture, whether through direct contact with liquid water or via the condensation of Shear cracks riddle the exterior wall of At this garage, movement-related cracking this urban parking structure. worsened as embedded steel corroded. ambient humidity. As steel corrodes, it expands; the volume of rust is greater concrete. applied during erection of the struc- than that of the original steel from ture, wood and concrete members which it formed. The pressure of the A variety of other chemical reactions begin to sag permanently by a small swelling steel is then transferred to the can also cause dimensional changes amount, eventually stabilizing after the surrounding concrete, brick masonry, and deformation in building materi- first several years of the life of the glazing, or other material, causing als, which place sufficient strain on the building. Concrete, a seemingly solid movement and cracking. components to cause cracking and threaten the structural integrity of the mass, has some fluid properties, which Carbonation takes place when hy- assembly. cause deck slabs to thin and expand drated Portland cement in concrete in length. Other building materials, like reacts with carbon dioxide in the air. Structural Deflection brick, exhibit only negligible creep in Although the reaction leads to an In response to the variety of forces response to applied loads. However, if increase in the mass of the concrete, acting on the building envelope, the attached rigidly to a wood or concrete it also causes a reduction in volume. components will undergo deforma- frame, masonry may sustain stresses Not only does carbonation lead to tion and movement. In addition to from movement of the adjoining concrete shrinkage, it also reduces the the dead loads (forces that remain member. alkalinity of concrete, making the em- relatively constant, i.e. the self-weight bedded reinforcing more susceptible of the building envelope) and live loads Settlement to corrosion. (changing forces related to building us- When the soil beneath a building Alkali Silica Reaction (ASR), character- age) that should be considered as part shifts, expands, or contracts, founda- ized by fine patterns of cracking in of the design of a building, environ- tion settlement can cause displace- concrete, is an expansive reaction mental forces that can cause structural ment and cracking of the facade, espe- between minerals in some aggregates deflection include wind, soil settle- cially where settlement is nonuniform and alkali hydroxides in the cement. ment, snow loads, and the seismic and one portion of the building settles The reaction forms a gel that absorbs forces of earthquakes. Vertical dead more than another. Proper site prepa- water and expands, exerting tre- and live loads, including the weight of ration and appropriate foundation de- mendous outward pressure on the the building element itself, cause hori- sign can prevent differential movement zontal members like beams and lintels and limit uniform settlement to within to deflect vertically, while columns, an acceptable range. bearing walls, and building frames tend to shift horizontally from the lateral Other Causes of Movement forces of wind and seismic events. The Displacement and deformation of building envelope needs to be adapt- building elements is a complex topic, able to these changing forces. and much remains to be researched Sustained, excessive loading may lead regarding the inter-relationship among to irreversible deformation known as the dimensional stability characteris- Solutions for copper roofs: lapping cleats creep or plastic flow, from which the tics of materials, the external forces that allow sheets to slide (standing seam, material does not fully recover even impingent on a built structure, and right) or small sheet sections (flat seam, left). if the load is removed. Once a load is the interaction between dissimilar

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components. Therefore, precise pre- that a brick facade could expand by some shrinkage will still occur. Weak diction of building element move- several inches flies in the face of ob- in tension, concrete that is rigidly fixed ments is not usually achievable. Factors ject permanence, the idea that objects to other parts of the structure will such as temperature at installation, age remain constant over time. Despite crack when subjected to the tensile of materials, ambient humidity, and in- evidence to the contrary, it may be stress from shrinkage or temperature- dividual variation in composition even reassuring to persist in thinking that induced contraction. Incorporating among relatively uniform materials, the concrete poured today will remain temperature reinforcement, typically as well as a range of other variables, dimensionally stable a year from now, steel bars or welded-wire fabric, into make exact calculations impossible. as opposed to facing the discomfort- the slab provides resistance to com- Fortunately, enough is known about ing fact that a solid material can shrink, pressive forces and reduces shrinkage the most common mechanisms of distort, and, even, flow. cracking. This practice is commonly building movement that conserva- The tendency to disregard changes in employed for parking garage decks, tive estimates can guide design in building materials notwithstanding, it is which are subject to large tempera- accommodating typical anticipated advantageous to avoid inadvertently ture swings, as well as for building dimensional changes. To avoid over- or constraining forces of movement, floor slabs. underestimating movement, design which can become so great under Design professionals can manipulate professionals should use the discretion restraint that they rip the building those characteristics of materials that born of experience to select appropri- apart. To prevent the adverse effects contribute to movement. Specifying ate tolerances. of restrained movement, the design light colors or shading devices reduces professional has two main strategies: temperature range at the building Strategies for Accommodating strengthen building materials to resist exterior. Allowing materials with Movement stress and limit movement, and incor- high irreversible initial shrinkage, like The principal cause of movement- porate movement joints to provide concrete or cast stone, to mature related cracking and displacement of flexibility for buildings to move ac- before use cuts down on movement building materials may be thought of cording to their natural tendencies. after installation. Seasoning of wood as a failure of imagination. Accustomed Material Strengthening limits moisture-related expansion and to thinking of our world in terms of contraction. the mobile (people, vehicles, animals) To enable materials to better resist Movement Joints and the stationary (earth, rock, build- the stress of anticipated movement, ings), it is easy to forget that these strengthening is common practice Despite construction practices that categories are imprecise at best and in building design and construction. limit shrinkage, expansion, bowing, and often inaccurate. This classification sys- For example, manufacturers aim to heaving, buildings will still move. Under tem is the reason earthquakes are so limit shrinkage in concrete by using restraint, the stress of tension or deeply unsettling (earth = stationary) the smallest amount of water that compression builds until it is released and broken-down cars so infuriating still affords the requisite strength and in the form of cracks, displacement, or (cars = mobile). It is also why buildings workability, along with adequate moist breakage. Provisions should be made tend to be under-designed as relates curing. that allow the building to readily adapt to provision for movement. Imagining However, despite these precautions, to dimensional changes and the effects

Brick expansion leads to vertical and step Bowing and displacement in brick masonry Relieving angles and horizontal joints cracking as forces seek pathways to relief. are symptoms of restrained movement. support masonry and allow for expansion.

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of variable environmental conditions. Movement joints divide the building Design of Movement Joints into discrete segments and allow each Movement joints must not only allow for dimensional changes, but also act in- section to move relatively indepen- tegrally with the building enclosure to support necessary floor loads, maintain dently. Used in combination across the fire separations, protect against noise, thermal transfer, and air and moisture exterior envelope, the various types infiltration, and, in the case of plazas and garages, minimize tripping hazards of movement joints include construc- and carry traffic. Joints must do all this and be durable and maintainable, with- tion joints, control joints, expansion standing season after season of use without premature degradation or wear. joints, isolation joints, and sliding joints. Some joints function only in a push-and-pull manner, along one plane, while Especially for large buildings or those others accommodate shear motion. Joints must be of sufficient size to handle with a complex geometry, joints are movement, without being so large they are difficult to weatherproof or com- critical to creating simpler units that promise the building aesthetic. The anticipated direction and extent of move- can respond to tensile or compres- ment will guide joint design, as will climate, location, and building geometry. sive forces without placing stress on adjacent building areas. Placement. Typically, building movement joints are located: • At periodic intervals along a continuous wall; Construction joints are used where • At changes in wall direction, including building corners and setbacks; construction work must be interrupt- • At wall openings, such as windows and doors; ed, primarily in concrete construction. • At changes in building height; Positioned where they are least likely • At junctions between areas subjected to differing climactic conditions; to impair structural strength, construc- • Between adjoining buildings; tion joints must allow some displace- • Between dissimilar materials; ment caused by thermal and shrinkage • At penetrations; movement, while transferring flexural • Below shelf angles; stresses from external loads across • Between panels in a veneer assembly; the joint. • At structural slab intersections in a concrete parking garage; and Control joints (also called contrac- • Between sheets of metal roofing. tion joints) create a plane of weak- At the exterior side of movement joints, sealants typically provide protection ness in concrete or other brittle from air and water infiltration. For longevity, it is important to select only seal- materials that tend to shrink, allowing ants with high expansion and compression capabilities, taking into consider- cracks to form at predetermined loca- ation adhesion to the substrate and resistance to weathering. tions, rather than randomly through- Vertical Joints. To allow for horizontal expansion and contraction along an out the material. Typically, control joints exterior wall, vertical expansion joints should be positioned to break the wall are gaps or grooves that are designed area into sections that share the same support conditions, exposure, and to open as the concrete shrinks. As construction. Joint spacing should take into consideration the amount of ex- with construction joints, these must be pected movement, compressibility of joint materials, and the size of the joint. located such that the structural integ- While no single recommendation can apply to all structures, a general rule rity of the concrete is not adversely of thumb for brick masonry cavity walls suggests placing vertical expansion affected. joints at approximately 20-foot intervals along a horizontal run of brick. Expansion joints separate large surfac- Horizontal Joints. Throughout the height of a wall, brick expands and con- es of materials, such as brick masonry tracts vertically. If the masonry were supported only at the bottom of the facades, glazed curtain walls, or plaza wall, not only would the multi-story stack crush the brick at the bottom, the terraces, into discrete segments, re- top of the wall would rise and fall during thermal cycles, ultimately increasing leasing stresses from changes in tem- in height as the brick absorbs moisture. To account for expansion and prevent perature, elastic deformation, moisture cracking, brick masonry is typically supported by horizontal relieving angles expansion, settlement, chemical action, (shelf angles) at regular intervals. These steel, L-shaped members are attached creep, and other forces. Expansion and to the floor slab or structural frame, typically at each floor. Horizontal expan- shrinkage are cumulative, so regularly sion joints below relieving angles provide space for vertical expansion of the spaced expansion joints reduce the brick and allow for deformation of the metal on which the brick bears. amount of movement that any one

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while allowing for dimensional changes. Where floor slabs and foundations adjoin cladding, or at intersections between banded wall materials, bond breaks, often in the form of building paper or flashing, allow independent movement of the different elements. Differences in temperature or mois- Shattered glass and displaced concrete Metal cladding displacement and ture between the top and bottom of a block due to building enclosure movement. exposure of underlying structural steel. concrete slab may cause deflection of the concrete called curling, which can joint must accommodate. At corners, little more than score marks in the crack facade materials directly sup- offsets, and setbacks in the facade, material, or they may be filled with an ported by or bonded to the slab. In cladding materials like brick masonry inelastic compound. Others, like ex- addition to construction practices that will expand horizontally toward the pansion joints, contain flexible foam or minimize concrete shrinkage, such as corner, forming long, vertical cracks pads. Selecting the appropriate type, limiting water content and increasing and displacement if expansion joints size, spacing, and location of joints can the size and proportion of course ag- are not provided. make the difference between a build- gregate, separating the structural slab Building expansion joints are to the ing that weathers the seasons and one from the exterior wall with a bond whole building what expansion joints that succumbs to premature cracking break can prevent the facade from are to a single building element: they and deterioration. cracking. Bond breaks may also prove divide the building into sections, so useful to isolate bands of different that stresses from one portion do not Differential Movement cladding materials. compromise the integrity of the entire Many brick masonry cavity walls use The main consideration for materials structure. These wide, flexible joints concrete block as back-up, a situation with different movement properties, extend through the building to create that leads to differential movement whether they be exterior wall com- smaller units that move autonomously. problems. After installation, brick tends ponents, roofing materials, or plaza to expand, while concrete shrinks. If Isolation joints allow for movement and terrace elements, is to provide the two are tied together rigidly, the between dissimilar materials or be- structural support while allowing wall will bow, deflect, and crack as tween old and new construction. For independent movement. Connectors brick and concrete pull against one an- example, building frames constructed that permit movement in one direc- other. Eventually, the ties binding face of concrete or steel will move differ- tion (e.g. along the plane of a wall) brick to concrete backup can break ently than will brick veneer, leading to and resist movement in another (e.g. under strain, rendering the brick ve- spalling and bowing if not accommo- perpendicular to the wall) and flash- neer structurally unsound and liable to dated. Similarly, concrete slabs adjoin- ings that create slip planes along lintels fall from the building. Flexible anchors ing walls, columns, or pipes will crack and angles are strategies that allow that can accommodate differential under restraint unless isolation joints for certain types of movement while movement, in conjunction with suffi- are provided at the material interface. holding the envelope system stable. cient cavity clearance, provide support Sliding joints are typical of traditional wood detailing and allow compo- Planning for Movement in Modern nents to slip past one another as they Construction expand and contract. Standing seam As advances in material technology copper roofs use this principle to al- have allowed for thinner and higher- low the sheets to slide, while still being strength building enclosure materials, secure. the science of building movement Each type of movement joint is in- has become central to the successful tended to serve a specific function, so implementation of these new exte- they may not be used interchangeably. Inadequate space for the steel relieving rior assemblies. While innovations in Some, such as control joints, may be angle has caused this wall to bow outward. extraction, fabrication, and structural

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Material Movement Building materials expand, contract, stretch, deform, creep, and swell. Hoffmann Architects designs solutions to building enclosure distress due to restrained movement and unforeseen dimensional changes, and we develop design strategies that allow building materials the flexibility to move Washington Masonic Prudential Plaza Building, Southern CT State Univ., according to their natural tendencies. Memorial, Alexandria, Virginia, Newark, New Jersey, Marble West Campus, New Haven, Our projects involving movement- Earthquake Damage Evaluation. Panel Facade Consultation. Connecticut, Facade Consultation. related rehabilitation include: NYC Health+Hospitals/Kings County Morgan Stanley Georgetown University, Brooklyn, New York Purchase, New York Ryan Hall and Isaac Hawkins Hall Building Envelope Rehabilitation Garage Repair and Site Rehabilitation Washington, District of Columbia Exterior Restoration Travelers Tower The George Washington University, Hartford, Connecticut Lisner Auditorium Sikorsky Aircraft, Plaza Renovation Washington, District of Columbia Administration Building National Historic Landmark Restoration Stratford, Connecticut ARINC Headquarters Facade Replacement Annapolis, Maryland G. Fox Building Facade Investigation and Repair Hartford, Connecticut Columbia University, Mudd Hall Masonry Veneer Stabilization New York, New York Roberto Clemente and Riverbank Parapet Repairs State Parks 4 New York Plaza Mandarin Oriental Hotel New York, New York New York, New York Washington, District of Columbia Masonry Facade Consultation Facade Consultation and Repairs Earthquake Damage Assessment Pickwick Plaza Rockland Psychiatric Center Fairfield Warde High School Greenwich, Connecticut Orangeburg, New York Fairfield, Connecticut Facade Repair Facade Investigation Masonry Wall Repairs Parking Authority of Baltimore City One American Row Countee Cullen Library Baltimore, Maryland Hartford, Connecticut New York, New York Assessment and Repair of Eight Garages Pedestrian Bridge Rehabilitation Exterior Rehabilitation The Bowery Hotel Ericsson, Piscataway Campus Smithsonian Institution, New York, New York Piscataway, New Jersey Donald W. Reynolds Center for Facade and Roof Rehabilitation Roof Replacement American Art and Portraiture Aramark Tower Verizon, 95 William Street Washington, District of Columbia Philadelphia, Pennsylvania Newark, New Jersey Copper Roof Replacement Facade Rehabilitation Partial Facade Reconstruction

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(continued from page 6) framing allow for cost-effective en- considerations in the design process. closure systems, the downside is that Rehabilitation of contemporary exist- JOURNAL is a publication of Hoffmann the beneficial qualities of these new ing buildings often involves remedia- Architects, Inc., specialists in the materials come at the expense of tion of movement-related distress, in rehabilitation of building exteriors. The firm’s work focuses on existing struc- other properties. Brick masonry that is the form of cracking, displacement, tures, diagnosing and resolving prob- brittle and thin stone that tends to dis- spalling, and, even, structural failure. lems within roofs, facades, windows, tort and bow demand more aggres- Periodic evaluation should aim to waterproofing materials, structural sys- sive strategies for managing movement tems, plazas/terraces, parking garages, identify early warning signs of re- and historic and landmark structures. than did the stolid mass walls of the strained movement, from longitudinal past. We also provide consulting services for cracks at building corners to shifting new building construction, as well as Historic loadbearing mass walls were of parapet walls, with a rehabilitation litigation and claim support. not built with expansion joints, but the plan to rectify the condition before it For address changes, free subscriptions, compression from dead and live loads becomes hazardous. For new con- or information on the topics discussed tended to offset the effects of move- struction, design should consider the in this issue, contact our Marketing ment. For modern structures, judicious anticipated behavior of all proposed Department at 800-239-6665, use of movement joints, isolation of materials in relationship to one anoth- [email protected], or: materials with differing movement er and to the environment, anticipating 2321 Whitney Avenue properties, and careful selection of and allowing for dimensional and vol- Hamden, CT 06518 materials appropriate to the expo- ume changes without compromising 203-239-6660 sure and stress conditions are critical building integrity. 1040 Avenue of the Americas, Ste. 14C New York, NY 10018 212-789-9915

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Cracks at foundation-cladding interfaces (left), crumbling pavers at expansion joints (center), Editor/Production: Alison Hoffmann and displaced stone or masonry (right) point to insufficient provisions for material movement.

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