Design Guide for Parapets: Safety, Continuity, and the Building Code

I S S U E 4/2020  VOLUME 37  NUMBER 4

Journal of architectural technology published by Hoffmann Architects, Inc., specialists in the rehabilitation of building exteriors. Design Guide for Parapets: Safety, Continuity, and the Building Code

Juan Kuriyama, AIA and Eric Au, LEED Green Associate

O riginally designed to protect environmental forces by relying on the against enemy attack, the parapet in weight of the wall. Due to construc- modern construction is far removed tion failures and the development of from its antiquated roots. Though the new materials and building systems, word parapet is derived from the modern parapets, constructed of Italian parapetto, meaning to guard/ diverse materials from reinforced con- defend (papare) the chest (petto), the crete to masonry to steel, have since parapet serves many other purposes, incorporated provisions for structural foremost among these as a critical reinforcement, along with accommo- transition between the building facade dations for moisture mitigation, such and the roof. as in-wall flashings and vapor barriers. Characterized as a low wall, the para- Parapets serve not only as a functional pet projects above the roof plane and building component, but also as an typically spans around the perimeter aesthetic statement. By incorporating of the roof area. Historically, para- elements such as cornices, bands, pedi- pets were constructed of masonry, ments, balusters, and embattlements, a consisting of multi-wythe walls with parapet can provide a continuation of mortar-filled collar joints, capped with the facade, or a visual termination. a coping. Usually unreinforced, these masonry walls were built to withstand As building performance standards progress, today’s design professionals face the compound challenge of balancing stringent building codes with the needs of the building owner. As underscored by the codes and standards dictating the design detailing of the critical transition between the facade and roof, this often-overlooked building element can have a big impact on the overall performance and longevity of the structure.

Design to Meet Code Requirements

Parapets vary from plain to ornate, but all must provide stability and moisture protection. Fundamentally, the parapet serves many practical purposes beyond its

Juan A. Kuriyama, AIA, Vice President and Director, Architecture with Hoffmann Architects, leads project teams in addressing building enclosure challenges for parapets, roofs, and exterior walls. Eric Au, LEED Green Assoc., Project Coordinator, develops engineering solutions that balance rigorous design with practical considerations. JOURNAL

original function of protecting in- rest assured that Basic Parapet Components habitants from invasion. The modern the development parapet must provide fire protec- of precise details COPING tion, serve as a fall-protective guard, can promote transition and protect the roof/facade the longevity of interface, conceal rooftop equipment, a parapet and and contribute to the aesthetic char- prevent common acter of the building. As knowledge issues like freeze/ about building science has evolved, thaw deteriora- OUTBOARD CLADDING building codes have been developed tion from arising. INBOARD CLADDING to disseminate standards for the safe The goal is to di- and functional design of parapet walls, minish the impact and design professionals must consider of moisture on these regulations when designing or the wall assem- rehabilitating parapets. bly by redirecting IN-WALL FLASHING The International Code Council’s water away from International Building Code (IBC) is the the building. ROOF ASSEMBLY model code for the design of para- Copings pet wall heights, structural stability, resistance to the elements, configura- The first line of tion, and anchorage. However, each defense for a state and local municipality may adopt parapet is the coping. Somewhat different versions of the IBC, as well STRUCTURAL ROOF DECK as code requirements more stringent larger than the than or different from those found in width of the wall, the model code. the coping serves as a protective Weather Barriers and Moisture cap situated atop the parapet assem- coping in place. Other older parapet Management bly. Copings are usually constructed walls use steel anchors, which tend to of moisture-resistant materials, such corrode and expand when exposed At some point during their lifetime, as metal, terra cotta, stone, or precast to moisture. The force of the cor- parapets will experience some sort of concrete. Because moisture has an roding metal causes displacement and deterioration and will eventually face inherent cohesive property, or surface cracking in the surrounding masonry, a problems if not properly maintained. If tension, it is critical to provide ad- process known as rust-jacking. Stainless neglected, a parapet will evince com- equate slope on the top surface of the steel anchors offer an ideal solution, as mon building enclosure issues, such as coping to direct water onto the roof they resist corrosion when exposed moisture infiltration, corrosion, crack- and not the facade, and to prevent to moisture, while securely anchoring ing and spalling, displacement, open moisture from intruding into the para- joints, and failed flashings. the coping against sliding or blowing pet. Copings with drip edges break the off. For metal copings, non-corroding The central concern for parapet surface tension of water and diminish fasteners and cleats should be used walls is the mitigation and movement the risk of it running down into the in securing the sheet metal, includ- of moisture away from the building wall below. ing proper cover and under plates at facade. Older masonry walls were Insufficient or deteriorated coping an- joinery. It is important that all penetra- constructed without provisions for chors represent a potential fall hazard tions through the flashings be sealed moisture management, often leading in parapet wall assemblies. For ex- to prevent moisture infiltration. to water intrusion and freeze/thaw ample, traditional clay camelback cop- Cladding deterioration, whereby water trapped ings rely on the weight of the coping, within the wall freezes and expands, the interlocking connection between Historically, parapets were com- causing cracks, spalls, and displacement. units, and the mortar bond between posed of a single, monolithic element Concerned building owners should the coping and wall to secure the beneath the coping, serving the dual

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Typical Brick Masonry Parapet Assembly that has softened, broken apart, or cracked is caused by thermal move- COPING ment of masonry elements and/or TRANSVERSE COPING JOINT freeze/thaw cycles. Openings in the

COPING ANCHORS joints admit further moisture and gen-

DRIP erate an ongoing problem that could MORTAR BED proliferate. SHEET METAL FLASHING Selecting an appropriate repair mortar VAPOR BARRIER that will match the existing mortar in color, profile, hardness, and tex- STEEL REINFORCEMENT BAR ture is key to long-term performance. Equally important, accurate mortar EXTERIOR FACE BRICK MASONRY matching maintains consistent appear- BRICK TIES & WIRE ance and performance, especially for REINFORCEMENT historic structures. The Brick Industry FULLY GROUTED Association (BIA) Technical Note CONCRETE MASONRY UNITS (CMU) 46, “Maintenance of Brick Masonry,” provides guidelines for formulating, STRUCTURAL ROOF SLAB testing, installing, and tooling repointing mortar. INTERIOR FACE BRICK MASONRY ROOF ASSEMBLY Though repointing mortar joints may SHEET METAL FLASHING & COUNTER-FLASHING seem like a quick fix, issues such as unmitigated exposure to weather or moisture should be resolved first, to address the root cause of persistent deterioration. Otherwise, problems function of structural support and infiltration, so it is important to iden- are likely to recur and lead to wasted weather-resistive barrier. In modern tify and replace compromised sealant money, effort, and time attempting to construction, parapets tend to have joints promptly. chase after a systemic problem with short-term repairs. a structural core, often of concrete Conversely, installation of sealant for masonry units (CMU), brick, concrete, masonry applications is not always In-Wall Flashings steel, or metal studs, with outboard the appropriate solution and should Under-coping flashings are a sec- and inboard cladding that might be used conservatively. If a parapet ondary layer to further mitigate the consist of brick, stone, stucco, metal is designed for mortar, it is usually infiltration of water into the parapet panels, or exterior insulation and fin- a good idea to stick with mortar, as wall. Sandwiched between the coping ish systems (EIFS). These compound properly designed brick masonry walls stone and wall assembly, the flashing assemblies offer more design options are intended to get wet and dry out. should be comprised of corrosion- and integrate thermal and moisture Sealant at joints intended for mortar resistant metal. Any penetrations, such control layers, but they demand skilled will trap water within and promote as anchors in the flashings, should be detailing of the various components to freeze/thaw damage. sealed. provide an uninterrupted, continuous barrier against the elements. Mortar Joints While under-coping flashings pro- Masonry construction is especially vide an effective means of preventing Sealants susceptible to moisture. In the case of moisture from entering the wall, there Sealant and backer rods are typically brick masonry parapets, architects and is a direct impact to the appearance of installed at the joints between copings, engineers will often look for signs of the parapet. In most cases, a continu- known as transverse joints. Failure of mortar joint deterioration as indica- ous, shiny drip edge is visible under- sealant at transverse joints between tors that there may be underlying is- neath the coping and may not be coping stones leads to moisture sues within the parapet. Often, mortar desirable from an aesthetic standpoint.

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the local author- moisture, and thermal management, ity having juris- coordination among trades and ap- diction (AHJ), propriate construction sequencing are parapet walls may key considerations to avoid compro- need to meet this mising the integrity of one system requirement. through the installation of another. A continuous vapor Structural Considerations barrier behind the exterior cladding Subjected to wind and weather on of the parapet both the outboard and inboard side, should provide parapets are especially vulnerable to Unstable parapets may be secured temporarily with netting. a clear drain- rain, wind, snow, and thermal forces. age plane that These stresses, or loads, are the basis Moreover, for historic and landmark redirects water away from the build- for determining the structural capacity of a parapet. Notably, wind loads act- structures subject to review by a pres- ing and allows moisture in the form ing on the perpendicular face generate ervation commission or other author- of vapor to escape from the interior. an overturning moment, or the force ity, such an alteration may be prohib- Typically, the vapor barrier encap- attempting to topple the parapet. ited. The design professional should sulates the top of the parapet wall Therefore, it is especially important to exercise good judgement in balancing directly underneath the coping, tran- provide reinforcement that restrains the performance of the parapet with sitioning along the vertical face of the parapet walls against anticipated lateral the visual impact of under-coping wall, and down onto the horizontal loads, which act perpendicular to the flashings. face of the roof level. Self-adhered and vertical face of the wall. liquid-applied air and vapor barrier At the transition between the parapet systems prevent moisture from travel- Often, parapets require incorpora- and roof, in-wall flashings provide a ing beneath the membrane, providing tion of steel reinforcement bars to seamless transition between the vapor an additional waterproofing redun- deliver the necessary structural stabil- barrier within the parapet wall and the dancy while also allowing the wall as- ity. Alternatively, structural piers or roof assembly. The National Roofing sembly to dry if water does get in. pilasters built out from the walls can Contractors Association (NRCA) provide additional lateral support. For Depending on the climate zone, the Roofing Manual recommends posi- much taller and thinner walls, instal- International Energy Conservation Code tioning in-wall flashings at least eight lation of steel bracing secured to the (IECC) requires that the building ther- inches above the finished roof assem- structural roof deck may be neces- mal envelope be provided with a va- bly to allow adequate height for instal- sary. The bracing system should be por barrier and continuous air barrier. lation of roof flashings, insulation, and designed by a qualified engineer or membranes, and to provide protec- Energy Efficiency architect to resist the required design tion from snow accumulation. Given loads, based on the geometry and changes in energy code requirements In addition to requirements for air construction of the parapet. in recent years, it may be prudent to or vapor barriers, the IECC requires allow additional space below in-wall continuous insulation across wall and flashings to accommodate increases in roof systems, including parapets. Based insulation thickness. on the climate zone, building use, and construction materials, the energy Vapor Barriers code dictates minimum R-values, or According to IBC 1403.2, “Weather insulating effectiveness, as determined Protection,” the building enclosure by the type, thickness, and density of must provide “a weather-resistant the insulation. As with air and vapor exterior wall envelope.” Based on the barriers, continuity for insulation in code in effect at the time of original complex parapet assemblies should construction, the extent of rehabilita- be documented in the design details. Stainless steel anchors secure coping tion work, and the interpretation of With various control layers for air, stones against displacement.

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Wind Loads to assess whether parapets meet the height requirements of the building Parapet Construction Building components are subjected to code in effect at the time of construc- wind forces that vary based on build- tion. Should a parapet fail to meet this ing profile, orientation, and the profile standard, corrective action, such as of each building element, factors which installation of a code-compliant guard- considerably alter the pressure dif- rail or reconstruction of the parapet, ferences at various points along the may be required. Depending on the building exterior. Studies have shown historical significance and construction that parapets offer some relief for roof of the building, these code-compliant assemblies in resisting wind uplift, as changes may also impact the aesthetic parapets reduce wind pressures at the of the parapet. roof perimeter. Nevertheless, parapets Steel bars reinforce the concrete themselves experience stress due to As previously discussed, evolving masonry unit core of the new parapet. wind loads, which must be considered energy codes demand increased roof in the design. insulation thickness, which directly impacts the height differential between The IBC provides structural re- the roof assembly and the top of a quirements for design wind pres- parapet wall. When planning to rebuild sures, citing the American Society of a parapet or install a new guardrail, Civil Engineers (ASCE) Standard 7, building owners should anticipate any “Minimum Design Loads for Buildings changes in the roof assembly thickness, and Other Structures,” as a basis of which impacts not only the height of reference for understanding wind the parapet itself, but also the height loads and their impact on buildings. of related flashings. Likewise, plans to Height Requirements augment roof insulation should incor- A liquid-applied air barrier provides a porate necessary extension of parapet continuous layer of moisture protection. The height of a parapet is governed and/or guardrail height, as well. by local building code. Many such codes are based on IBC 705.11.1, Accommodation for Movement “Parapet Construction,” which stipu- While it is normal to think that lates that “the height of the parapet buildings are relatively static, build- shall be not less than 30 inches above ing materials experience movement the point where the roof surface and in the form of growth, shrinkage, and the wall intersect.” However, while deformation in response to environ- a 30-inch parapet might satisfy the mental changes. As the temperature IBC model code, design professionals rises, materials tend to expand, then should check state and municipal code contract when the temperature falls. Brick ties anchor the cladding to the requirements, as some jurisdictions Inherent material properties may also CMU structural core. have stricter rules for parapets acting cause dimensional changes over time, as fall-guards. with dissimilar materials, such as con- For example, the New York City Building crete and steel, expanding or contract- Code requires buildings taller than 15 ing at different rates. feet to have parapets with a minimum Expansion joints are designed to ac- height of 42 inches. (Buildings con- commodate movement within a structed prior to 1938 are exempt wall and allow for differential move- from the requirement, provided that ment between dissimilar materials or no significant repairs are performed across large expanses of wall. These on the parapet.) New York City’s periodic breaks within the wall are Facade Inspection and Safety Program fitted with a compressible filler and With the copings and flashing in place, the parapet is nearly complete. (FISP) requires design professionals sealed at the joints. Since walls tend to

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of the problem. Corroded anchors, for instance, can be readily addressed through replacement with corrosion-resistant materials. If, however, maintenance is deferred, the outward pressure from corrosion may lead to cracking and displacement of copings and masonry, necessitating more extensive rehabilitation. Flashings are critical to moisture management. Under-coping flashings(left) direct water away Similarly, timely identification of mois- from the parapet and exterior wall, while base and counter-flashings (right) protect the roof. ture infiltration and installation of proper flashings prevents water from expand exponentially outward from parapet. To understand the original entering the parapet. If left to persist, the center, with the greatest degree design intent and confirm the details water intrusion can compromise the of movement towards their ends, it is of the assembly, access to original and structural integrity of the parapet and especially important to provide expan- record drawings is highly beneficial. will likely warrant a rebuild with struc- sion joints at or near building corners, Particularly for older structures, these tural provisions in place. as well as at offsets, setbacks, and wall drawings are not always available, or, For parapets classified as historic or intersections. Though this a general even when they are, they do not accu- architecturally significant, limiting the recommendation for brick masonry, rately reflect what was constructed in scope of intervention is often pre- the designer should take into consid- the field. However, an experienced deferred. In severe cases where a para- eration the specific building materials, sign professional can make a probable pet requires rebuilding, reconstruction the degree of expected movement, diagnosis based on common construc- necessitates coordination with historic compressibility of the specified joint tion practices. Exploratory probes into preservation offices in determining the filler, and the size of the joint relative the parapet wall may provide valuable appropriate strategy for restoration to the structure at hand. information about the overall con- and code compliance. To accommodate for vertical expan- struction, exposing deficiencies that sion, continuous horizontal joints in would otherwise be concealed. Where parapet deterioration is acute, the exterior cladding are usually locat- temporary stabilization may be neces- ed below the parapet and roof level. Repair or Replacement sary to protect the public from loose The horizontal joints generally consist While it is impossible to guarantee or unsecured materials. Nylon netting of steel relieving angle supports with that a parapet will not experience and metal straps are commonly used compressible filler pads anchored to some sort of decline over time, there to stabilize a parapet wall until a more the structural backup. are steps that can be taken to pre- permanent solution can be imple- mented. Additional public protectives, Eventually, a parapet wall will display vent, treat, and repair common issues. such as sidewalk sheds, may be man- signs of distress if provisions for ex- Depending on the extent and nature dated for certain repairs, especially in pansion and movement are not pro- of deterioration, maintenance repairs urban locations, where a deteriorated vided. This stress propagates along the may be sufficient in limiting the scope parapet poses a threat to public safety. structure and may be observable as continuous step cracks or bowing and To avoid the expense and disruption displacement. To prevent hazardous of reconstruction, routine parapet conditions, parapets must be evalu- maintenance and monitoring are vital ated routinely for initial warning signs in addressing emerging problems and of restrained movement. preventing deterioration. “Band-aid” repairs may temporarily defer issues in Assessing an Existing Parapet the short-term, but, ultimately, only a There are several tools that can assist well-designed and properly maintained the engineer or architect in determin- parapet will avoid chronic problems ing the construction of an existing Open mortar joints lead to deterioration. and stand the test of time.

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Parapet Rehabilitation The Broad Exchange Building New York, New York Exposed to the elements on all sides, Pediment Parapet Reconstruction, parapets are keenly susceptible to the Facade Restoration effects of time and weather. Moreover, their orientation perpendicular to Barnard College, 600 West 116th St. wind means they must endure lateral New York, New York forces without structural failure. The Facade Repairs, Parapet Reconstruction integrity of the building enclosure St. John’s University, Newman Hall depends on the soundness of Queens, New York parapets, and Hoffmann Architects has Parapet Restoration Design spent more than 40 years investigating, Bullard-Havens Technical High School designing, and rehabilitating a wide Bridgeport, Connecticut variety of parapet types and materials. Parapet Rehabilitation and Roof Our parapet projects include: Replacement Kings County Hospital Center Solow Residences, 265 East 66th St. Columbia University, 44 Morningside Dr., New York, New York New York, NY, Building Envelope and Parapet Brooklyn, New York Rehabilitation. Facade, Clay Tile Roof, and Parapet Parapet Reconstruction Rehabilitation SUNY Purchase College Middlesex Hospital Verizon Building, 95 William Street Purchase, New York Outpatient Center Newark, New Jersey Parapet Reconstruction and Roof Middletown, Connecticut Facade and Parapet Replacement Replacement Parapet Leak Repairs Jolly Hotel Madison Towers Fountain Terrace Condominiums Columbia University New York, New York Stamford, Connecticut Dodge Physical Fitness Center Parapet, Facade, and Roof Investigation Parapet Reconstruction New York, New York and Repair Park City Plaza, 10 Middle Street Parapet Reconstruction Bridgeport, Cohen and Wolf Law Offices Connecticut Bridgeport, Connecticut Parking Garage Facade Investigation and Parapet Parapet Investigation Rehabilitation and Repair Queensborough Community College Interchem Building Medical Arts, Sciences, and 1133 Avenue of the Administration Buildings Americas Bayside, New York New York, New York Roof and Parapet Replacements Facade and Parapet Schering-Plough Headquarters Investigation and Kenilworth, New Jersey Smithsonian Institution, Freer Gallery of Art, Washington, DC, Repair Mortar and Parapet Leak Investigation. Roof, Parapet, and Coping Rehabilitation

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(continued from page 6) Diverse Materials, Diverse applicable to a stainless-steel-clad Solutions parapet on a recently constructed JOURNAL is a publication of Hoffmann condominium. Architects, Inc., specialists in the Developing the best plan to prevent rehabilitation of building exteriors. The and treat the underlying issues with Whether the scope of work involves firm’s work focuses on existing struc- repairing an existing parapet or de- tures, diagnosing and resolving prob- parapets follows a proven strategy: in- signing and building a new one, design lems within roofs, facades, windows, vestigation of existing conditions, con- professionals have the responsibil- waterproofing materials, structural sys- sideration of construction quality, as- tems, plazas/terraces, parking garages, ity of developing a comprehensive sessment of historical significance and and historic and landmark structures. approach that balances the needs of We also provide consulting services for design intent, and evaluation of other building owners, the stipulations of new building construction, as well as factors specific to the structure and code requirements, the material and litigation and claim support. situation. A rehabilitative approach that structural properties of the wall con- works for a masonry parapet on an For address changes, free subscriptions, struction, and the aesthetic qualities of or information on the topics discussed 18th century church is not necessarily the building. in this issue, contact our Marketing Department at 800-239-6665, [email protected], or:

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Historic parapets, such as this brick masonry parapet with stone copings and ornamental Editor/Production: Alison Hoffmann railings, demand historically appropriate strategies that balance preservation with performance.

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