RoofViews

Building Science

Key Strengths of Four Green Building Rating Systems

By Benjamin Meyer

November 23, 2020

Foggy city

Designing for Moisture Durability and Energy Efficiency, Part 2

Part 1 of our discussion of Designing for Moisture Durability and Energy Efficiency explored the driving forces that result in the increasing interactive complexity and tight coupling of roofs and other building systems in modern green buildings. Part 1 also provided an overview of the various project life-cycle phases and compared the top green rating system's scope to address or not address moisture durability in those phases.

Introduction

This Part 2 blog reviews the key strengths of the same four green building rating systems in more detail as it relates to moisture durability. The following outlines the key takeaways from this portion of the assessment:

  • To accomplish long-term durability, it's recommended to manage moisture risks when interactive complexity and tight coupling are inherent in a roof and enclosure system design (see Part 1 for more on this).
  • It is recommended to use or borrow the best features from each green building rating system to shore up any project's moisture management specifications, regardless of the actual green building certification being sought.
  • This assessment demonstrates that none of the four green building rating systems, even when combined, currently address moisture durability across all of the project life-cycle phases.
  • The building enclosure commissioning process, in addition to the green building rating systems, can help design the enclosure so that it performs across the project phases for the long-term building performance.

Key Strengths

As a reminder, the four green building rating systems being addressed are:

Below are the notable key strengths of the four green rating systems, described across the project phases - material selection, design & procurement, construction activities, performance testing, operation & maintenance, and enclosure commissioning.

Material Selection Phase

Design & Procurement Phase

Construction Activity Phase

Performance Testing Phase

Operation & Maintenance Phase

Building Enclosure Commissioning

Conclusion

Noticeably absent from most of the categories above, the LBC™ v4.0 doesn't provide specific or prescriptive moisture mitigation requirements for many elements discussed.

To accomplish long-term durability with respect to moisture, it's recommended to manage risk when interactive complexity and tight coupling are inherent in a roof and enclosure system design. It is recommended to use or borrow the best features from each system to shore up any project's specifications. And if the owner is seeking a specific green rating system certification, be sure to look across the alternative rating systems to fill in the gaps where one may leave out elements or is vague regarding enclosure moisture durability. At the same time, be mindful that even when combined, none of the four green building rating systems currently address moisture durability across ALL of the project life-cycle phases. This is why utilizing the building enclosure commissioning process to more formally address the relevant moisture durability risks are being assessed by an enclosure professional can be an important step for green buildings. Designing the enclosure, including the roof system, to perform across the project phases can help manage risk for the long-term building performance.

For more information on designing for moisture durability considerations with green building certifications and individual credit assessments, register for the Continuing Education Center webinar, Addressing Moisture Durability and Energy Performance in Roof Assemblies: A Critical Review of Multiple Voluntary Green Building Certifications, sponsored by GAF and presented by Benjamin Meyer, AIA, LEED AP and James R. Kirby, AIA.


*Note: LEED® is a registered trademark of the U.S. Green Building Council; Green Globes® is a registered trademark of Green Building Initiative, Inc.; LBC™ is a registered trademark of International Living Future Institute; IgCC® is a registered trademark of International Code Council, Inc.

About the Author

Benjamin Meyer, AIA, LEED AP is a Roofing & Building Science Architect with GAF. Previous experience includes: enclosure consultant principal, technical management for enclosure products, commercial design, real estate development and construction management on a range of projects that included residential, educational, offices, and DuPont industrial projects. Industry positions include: Voting Member of the ASHRAE 90.1 Envelope and Project Committees, LEED Technical Committee member, past Technical Advisor of the LEED Materials (MR) TAG, and Director of the Air Barrier Association of America (ABAA).

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A city view through a window pane filled with water droplets
Building Science

Designing for Moisture Durability & Energy Efficiency

There can be a perception in the market that a "green building" is a better building, and that the risks associated with "building differently" are inherently covered by the green certifications driving the industry forward from a sustainability standpoint. Both better buildings and risk mitigation can be accomplished by green buildings, and this article will discuss some of the key principles to accomplish this for building enclosures and roof assemblies.Moisture durability of enclosure systems focuses on the interaction of the materials, assemblies, and their design configurations in the building. The goal of managing moisture durability is to establish performance expectations, allow enclosures to perform as intended, continue to perform through the project lifecycle, and be serviced or maintained in a way that minimizes risk of damage to the enclosure and performance of other critical building systems. This discussion is going to focus on the moisture durability aspects of buildings and how they relate to energy performance and lifecycle expectations. While other aspects of resilience are also important, these aspects target risks that are not necessarily related to climate change, but are related to the design of enclosure and roof assemblies directly.Moisture Durability in ContextThe American Institute of Architects defines olor: #333f48;"> as "mitigating risk for hazards, shocks, and stresses and adapting to changing conditions". Resilience goes beyond the minimum code requirements to address issues that influence long-term performance (more here about Sustainability and Resilience). The "hazards, shocks, and stressors" can come from external sources as well as from the design decisions of the built environment. Some are rare extreme events such as tornadoes and wildfires, and some are common and persistent adverse events, like moisture risks in the building enclosure. This perspective of moisture durability as a risk fits within many existing terms and goals that stem from Sustainability, Resilience, Adaptability, and Mitigation initiatives; moisture durability fits within these goals and is not separate from them.Moisture durability and energy efficiency are part of resilient designEnergy Efficiency is a Moving TargetThe minimum or baseline energy efficiency performance expectation has been improving over time. The cost-effective and validated energy saving of one of the underlying national energy standards has increased in each of ANSI/ASHRAE/IES Standard 90.1-2016 (ASHRAE 90.1) 3-year publications. The ASHRAE 90.1 – 2019 version has also recently been published and was validated by the Pacific Northwest National Laboratory as an additional 5% of savings over the previous 2016 version.Compounding the energy savings, green building rating systems generally require additional savings beyond the baseline and provide points for exceeding the baseline. In addition, the energy performance requirements within green certification systems are also improving. For example, the same energy savings that would have contributed 10 points to the LEED v3 rating system, is roughly equivalent to the starting energy savings required in LEED v4.1, which is currently in the pilot phase.Increasing efficiency requirements are compounded by green rating systems.Not every local jurisdiction is adopting the same base codes and standards, which leads to additional confusion in the design and construction industry.Interactive Complexity and Tight CouplingThe book Normal Accidents by Charles Perrow explains how significant technological advancement can lead to failures. Perrow describes two main components of "normal accidents." The first component being "interactive complexity" as a function of the number and degree of system interrelationships; when this factor is high surprises are expected. The second component is "tight coupling," the degree at which initial failures can concatenate rapidly to bring down other parts of the system; the more highly-linked surprises are not easily isolated and resolved. If a system has only one of the two components then it is still a risk but is more easily managed. When "interactive complexity" and "tight coupling" are combined, accidents could be considered "normal" or expected according to Perrow.As more materials and additional requirements are added to enclosures, it is important to recognize when materials and assemblies need to change in order to achieve higher energy performance. In a broad sense, as energy efficiency is improved in building enclosures, moisture risks can increase from decreased heat flow across the assemblies. The changes in enclosures can manifest as generally lower exterior surface temperatures (during heating months) as the exterior is less dependent on the interior space conditioning. As we improve energy efficiency, we may also be increasing moisture risks in building enclosures. And the increased risk may be more complex than the historical designs and more tightly coupled to the building's HVAC operations, structural elements, and occupant-use conditions.Energy efficiency improvements can lead to increased moisture risks in a building enclosureMoisture Management in Green Building Rating Systemsis tempting to assume that the building enclosure will work perfectly and water won't get where it doesn't belong. Such a belief can lead to a lack of risk mitigation from a very likely hazard (water) throughout the useful life of the building. A more realistic mindset is: moisture intrusion cannot be completely avoided, it must be managed. Enclosures should be designed to manage incidental water with minimal long-term impact. The key is for the enclosure design to have a greater capacity for drying than its risk of wetting.This moisture durability assessment looks at six primary categories for an enclosure. Roughly working across the project life-cycle, they are shown in the figure below:Moisture durability elements and assessment project life-cycle detailsFor the moisture durability assessment, the four most common green building rating systems available for new construction projects are compared against the six categories shown in the previous figure. The green building rating systems reviewed are:Leadership in Energy & Environmental Design (LEED®), version 4.1Green Globes®, version 2019Living Building Challenge (LBC™), version 4.02018 International Green Construction Code (IgCC®)Green building rating systems moisture durability summaryThis graphic summarizes each of the six individual detailed assessments reviewed across the project life-cycle phases. There is quite a range of results across the green building rating systems assessed.Key TakeawaysWhen designing for moisture durability and energy efficiency in enclosures and roof systems, consider all project phases. This includes utilizing the building enclosure commissioning process to more formally ensure the relevant moisture durability risks are being assessed by an enclosure professional. It is important to recognize that overlooking one of the project phases may result in unmanaged risk for the long term building performance. Some of the systems have direct coverage of individual elements of moisture risk mitigation, but the certification frameworks may not be sufficient to rely on to provide comprehensive moisture durability mitigation. This is especially important knowing all four rating systems have mandatory energy efficiency improvements beyond code-minimum requirements, but none of the four have a complete set of mandatory credits to accommodate the increased moisture risk associated with the added enclosure complexity.Check back for follow-up articles on moisture durability, including notable highlights from the green building rating system detailed assessment and an example applying the elements of moisture durability to a roof system.For more information on designing for moisture durability considerations with green building certifications and individual credit assessments, register for the Continuing Education Center webinar, Addressing Moisture Durability and Energy Performance in Roof Assemblies: A Critical Review of Multiple Voluntary Green Building Certifications, sponsored by GAF and presented by Benjamin Meyer, AIA, LEED AP and James R. Kirby, AIA.

By Authors Benjamin Meyer

May 06, 2020

Parapets on the side of a building
Building Science

Parapets Part 3: An Example of Complexity

Part 1 of our discussion of parapets (Continuity of Control Layers) explored the many reasons continuity of water, air, thermal, and vapor control layers are necessary for long term performance. In Part 2 of our discussion of parapets (Navigating Codes) discussed the challenges involved in navigating the range of national model codes and standards that will influence your design. In Part 3, we're providing a practical example of applying the control layer continuity principles to construction trade sequencing while identifying some common challenges. Control Layer Continuity To better understand common parapet challenges, it is important to review continuity across the roof and wall systems, specifically the key four Control Layers: Water, Air, Thermal, and Vapor. These four key Control Layers should generally be continuous across all six sides of building enclosures. It is difficult–but not impossible–to achieve effective Control Layer continuity across building systems, especially at significant transitions like a parapet, where the roof system meets the wall system. When beginning to think about designing enclosures, it's helpful to start with an ideal scenario. The configuration of the ideal wall system can be considered as follows: the cladding on the outside, continuous insulation keeping the rest of the control layers tempered in the middle, and structure to the inside. This "ideal" configuration can also be applied horizontally to the roof assembly. For an example of a transition, the roof and wall meet as an "ideal" flush edge with very simple transitions. As a system moves away from these ideal configurations, including parapets or other project constraints, transition details become more challenging and trade-offs have to be made. "Ideal" Roof and Wall Transition For more complex scenarios, like parapets, there are simple design tools to connect the control layers as they transition from the wall to the roof. The "pen test" — tracing each of the control layers across the building enclosure — is a helpful tool to design and communicate to the field the intent of the critical components and functions of the building enclosure. Discussing control layers as they apply to a roof or wall alone is fairly manageable. But the process gets much more complicated when the roof meets the wall at the parapet condition (more here in Part 1 about Control Layers). The "pen test" is relatively easy in theory, but it can get complicated as we zoom in and consider the control layers at each condition, penetration, and transition. Example of breaking down a parapet detail by the four control layers In summary, the following are key points to maintain continuity of the control layers: Water Control is managed by the roof membrane and the cladding. A secondary water control layer is often found against the structure, behind or below the exterior insulation. Air Control can be managed at the deck level of the roof, which can more readily be married into the wall air barrier. The roof membrane can also be used as an air barrier as long as the detailing and transitions are done carefully. Thermal Control continuity is maintained by connecting the roof and wall insulation, which can be challenging. It's important to be mindful of cavity insulation and the potential design risks of condensation at the thermal bridges. Vapor Control can also be in the same plane as the air control layer, based on location needs, construction methodologies, and occupant use of the building. Coordinating Complexity This section provides a practical example of applying the control layer continuity principles to construction trade sequencing while identifying some common challenges. When confronted with a similar design as the example below, a general contractor may request alterations to the design in order to shorten the schedule or reduce costs. However, this value engineering process—the reduction of cost and time—may also comprise continuity of the control layers and reduce the intended long-term performance of the parapet systems (more about Value Engineering performance impacts). If unsure or designing high-performance buildings, engaging a building enclosure consultant can help anticipate continuity and constructability issues. For the purposes of this discussion, the materials applied to the parapet assembly sequence (figures a – h below) are color-coded in their application step by their primary control layer function: Water Control elements are shown in "blue" Air Control elements are shown in "red" Thermal Control elements are shown in "yellow" Vapor Control elements are not shown separately (See the Vapor Control section above for applicability) To help identify separate materials within a control layer, lighter and darker versions of the color are used to distinguish elements within the same step. Also dashed, or "hidden lines," are used to depict materials edges that may be overlapped or behind another layer in the sequence the same step. (a) Initial condition a. In the initial condition, the wall and roof deck are assembled up to their sheathing. The roof structure is a corrugated steel deck with a substrate board placed on top to provide a continuous surface for later air barrier adhesion. The exterior wall is steel framed with cavity insulation and exterior sheathing applied. (b) Pre-treated corner b: In preparation for the parapet wall construction, a strip of air barrier material is applied to the roof and wall edge with sufficient material for future integration with the remainder of the continuous air barrier. It is important to note the material on the wall side is not yet adhered to allow for future lapping to manage water in "shingle fashion" as required by the IBC. This can be accomplished by leaving a portion of the release liner in place for adhered materials. (c) Parapet wall assembled c: The parapet wall is then assembled on top of the roof deck in a platform framed configuration. If lateral bracing for the parapet is required, additional detailing and coordination would be needed. (d) Air barrier integrated d: After the parapet wall is in place, the remainder of the continuous air barrier can be applied to both the roof and wall systems. It is notable that if the air control layer is also intended to act as the WRB in the wall and parapet system (as shown in (d)), the application should start from the lowest point and work upward; this allows the subsequent layers to be lapped in shingle fashion. After the air barrier is applied to the walls (light red), the pre-applied strip of material can be lapped and secured over it (dark red in the center of the wall). The air barrier can then be applied to the roof deck (light red), up the backside and over the top of the parapet wall, and then terminate downward on the outside of the wall, lapping over in shingle fashion (dark red at the top of the wall). Lapped edges hidden behind the layers of air barrier materials are shown with dashed lines. (e) Continuous insulation installed e: The roof insulation and high-density coverboard can now be installed to the roof deck. These could be mechanically-fastened or adhered roof systems, but the use of mechanical-fasteners through the entire roof insulation can have a significant effect on the thermal performance of the building (more on optimizing roof thermal performance). Continuous insulation is also applied to the backside of the parapet wall to maintain continuity. The parapet blocking for the coping cap can now be installed. In this case, it also includes a layer of tapered insulation to provide slope back to the roof area and extend the continuous insulation to the top side of the parapet. Wood blocking is included as required to accomplish fastening to meet ANSI/SPRI ES-1 uplift requirements. After the parapet blocking is in place, a piece of counter flashing (shown in blue) is required to lap over the WRB prior to the installation of the walls continuous exterior insulation; flashing will later lap over the coping cap, but without this piece pre-installed, there would be a discontinuity in the water control layer. The bottom edge of the flashing, under the wall exterior insulation, is shown as a dashed line. (f) Roofing and terminations installed f: The roof membrane is applied to the roof area. An expansion joint may also be added at the joint between the roof and the parapet wall to allow for any expected movement between the systems. The membrane is then lapped and seams completed at the horizontal roof edge, extended up the backside of the parapet wall and terminated over the previously installed counter flashing on the face of the coping blocking. Terminating and lapping downward on the outside of the parapet wall maintains the continuity of the water control layer and provides a shingle-lap onto the secondary water control layer on the wall. The membrane over the coping blocking will also act as a secondary protection below the future coping cap. The coping cap attachment cleats and spline flashing are installed to the top edge of the parapet wall, bedding and treating the fasteners in sealant where they penetrate the membrane. (g) Coping and cladding installed g: The exterior cladding is then installed to the outside of the parapet and exterior walls (light blue). The coping cap is installed at the top of the wall, over the cleats and blocking (dark blue). The coping cap should be attached with the cleats as tested for by ASNI/SPRI ES-1, lapped over the cladding with drip edges on both sides, and maintain an overall slope towards the roof system to shed water. Caption: (h) Final parapet assembly h: The parapet assembly is now complete. During the service life of the building, regular inspections and maintenance are needed to retain the performance of the parapet. Recovering or replacement of the roof system in the future should utilize as-built documentation to understand how to continue to manage the wall and roof system control layers. Enabling Success Designing to maintain continuity of the four key control layers is important to ensure long-term performance. To get the design intent implemented in the field, detailing and identification of the control layer(s) in the drawings and specifications is critical. This can require the design to be pretty specific – more than just "or equal" or "by others". Specifying materials with known compatibility is important. And if the sequencing of components and members in the field impacts the intended continuity or performance of the control layer in the design – it should be addressed. These challenges should be considered for every project. "Standard details" aren't able to capture project complexities such as high-to-low parapet transitions, terminations into a rising wall, and curtain wall flybys. These conditions all require unique detailing that must include continuous and well-conceived transitions. It's important to remember that control layer discontinuities can lead to failures in the field. For instance, air leakage can lead to concealed condensation, which can be mistaken for roof leaks. For more information on parapet and control layer continuity, register for the Continuing Education Center webinar, Parapet Predicaments and Roof Edge Conundrums, sponsored by GAF and presented by Jennifer Keegan, AAIA and Benjamin Meyer, AIA, LEED AP. For more information on parapet and control layer continuity, read the Continuing Education Center article, Parapets—Continuity of Control Layers, sponsored by GAF and written by Benjamin Meyer, AIA, LEED AP.

By Authors Benjamin Meyer

March 23, 2020

Two men on a parapet looking at their phones
Building Science

Parapets Part 2: Navigating Codes

Part 1 of our discussion of parapets (Continuity of Control Layers) explored the many reasons continuity of water, air, thermal, and vapor control layers are necessary for long term performance. In Part 2, we're discussing the challenges involved in navigating the range of national model codes and standards that will influence your design. Codes under discussion include the 2018 International Building Code (IBC), the 2018 International Energy Efficiency Code (IECC), and the ANSI/ASHRAE/IES Standard 90.1-2016 (ASHRAE 90.1). The summary provided in this article is not intended to be an exhaustive list of requirements for exterior wall and roof systems in the referenced national model building and energy codes. Different versions of the referenced codes have additional and/or different requirements; these requirements may also vary by adoption and modification by the local authority having jurisdiction. It is important to refer to local codes for the applicable requirements. The requirements for parapets generally come from the building code (IBC) and the energy code (IECC and ASHRAE 90.1). The requirements within the building and energy codes can be mandated prescriptively, as a performance threshold, or by reference through specific key standards. The performance standards are important because they don't attempt to regulate by providing exhaustive lists and itemized component requirements, like a prescriptive method. These performance requirements establish the design benchmark and then provide a methodology to demonstrate compliance with the benchmark. The building codes and standards do not always address parapets exclusively, but many refer to "Exterior Walls" separately from "Roof Assemblies". Summarized applicable code references for parapets. Exterior Walls in the Building Code The exterior wall requirements for parapets are covered in Chapter 14 of the IBC which addresses "exterior walls, wall coverings, & components." For parapets, the requirements for weather protection, water-resistive barriers (WRBs), managing vapor, and flashing apply as they do for the rest of the exterior building walls. IBC Chapter 14: Exterior Wall applicable area highlighted in blue. Exterior Wall Flashing Flashing is very important and is generally repeated in both the wall (IBC 1404.4) and roof provisions of the code. The IBC includes the principle that "flashing shall be installed… to prevent moisture from entering the wall or to redirect that moisture to the exterior." This is an important starting point for parapet design where the sequencing can be a challenge among numerous wall- and roof-system contractors. While not an exhaustive list, IBC 1404.4 includes a minimum list of areas requiring exterior wall flashing. These are summarized below: Penetrations and terminations Intersections with roofs, chimneys, porches, decks, balconies and similar projections Built-in gutters and similar locations where moisture could enter the wall Flashing with projecting flanges, installed on both sides and the ends of copings At all of the prescriptive flashing locations listed in the IBC, the purpose is two-fold. The first is for the flashing to be installed in a way that prevents water from entering the wall system. This concept is known as "shingle fashion," or installing components of the roof, exterior wall, and parapet "such that upper layers of material are placed overlapping lower layers of material to provide for drainage via gravity and moisture control" (IBC 202). Logistically, this is best accomplished onsite by applying materials from the bottom of the building to the top, so the next progressive layer or system is then lapped correctly. The second, and more challenging flashing requirement, is to also be installed in a manner that permits water to exit the wall system if it enters incidentally. This requires the parapet to be designed with a method and pathway for water to drain from the flashing, even from behind the cladding (think weep holes at masonry shelf angles). In addition to providing a means for drainage, the IBC also includes a drainage scenario to avoid exterior wall pockets (1404.4.1). Wall pockets or crevices are locations within a wall assembly "in which moisture can accumulate." These scenarios can be common in parapets where the exterior wall, roof, and parapet wall above might not always be in alignment. In parapets, these wall pockets should be avoided or protected with appropriate flashing for the application. Exterior Wall Weather Protection The Weather protection section (IBC 1402.2) requires that the exterior wall "shall be designed and constructed in such a manner as to prevent the accumulation of water within the wall assembly". One of the methods prescribed in this section is to include a secondary water management layer, or "water-resistive barrier" (WRB), behind the exterior cladding in the exterior wall portion of a parapet. Beyond including the WRB layer, "a means for draining water that enters the assembly to the exterior" must also be provided in the parapet wall design. There are exceptions to the secondary WRB and drainage requirements provided in the IBC for concrete and specifically tested systems, but the benefits for designed water control is applicable for all construction types. Exterior Wall Vapor Retarders In exterior parapet walls, protection against condensation is also required to be compliant with the vapor retarders portion (IBC 1404.3). Vapor retarder materials are separated into three classes by ASTM E96 testing (Procedure A, desiccant method): Class I: 0.1 perm or less; Class II: 0.1 Class III: 1.0 The vapor retarder classes are referenced in the IBC to identify by climate zone if a material is permitted in the assembly in a prescriptive manner (IBC 1404.3.1 and 1404.3.2). It is important to note that all materials have vapor retarding properties to some degree and may limit vapor transmission without the addition of a dedicated vapor control layer. This is also why the IBC includes the alternate performance compliance of providing a "design using accepted engineering practice for hygrothermal analysis" as described in the initial language of 1404.3. In most cases, if a vapor control layer is needed, it is a good idea to select a vapor retarder that will allow some amount of drying from diffusion. High-humidity interior environments such as natatoriums, manufacturing facilities, and grow houses may require a vapor barrier for long-term performance. However, the decision of whether or not to add a vapor control layer to a roof assembly is normally based on risk and is best made with a building enclosure consultant. The weather protection and vapor retarding sections of the IBC apply to exterior walls, but parapets may have very different design and performance requirements than the wall assembly below the roof. That is why it is important to maintain continuity of the four control layers at this interface. Roof Assemblies in the Building Code The roofing portion for parapets is covered in Chapter 15 of the IBC which addresses Roof assemblies, specifically the "design, materials, construction and quality" of roofs. Regarding parapets, the roof system requirements impact the wall where terminations and transitions occur. The requirements include weather protection, flashing, coping, wind resistance design, edge securement, and specific requirements for various types of roof coverings. IBC Chapter 15: Roof Assembly applicable area highlighted in blue. Roof Assembly Weather Protection The requirements for weather protection (IBC 1503) are fairly broad, requiring roof decks covered with approved roof coverings. Much more detail is covered in the additional IBC sections regarding roofing and parapets. In the roofing provisions, it is important to note that compliance with "the manufacturer's approved instructions" doesn't just affect a project's eligibility for warranty, but is also required for building code compliance. Roof Assembly Flashing The requirements for flashing (IBC 1503.2) are repeated in part across the wall and roof portions of the code. This repetition highlights the importance of managing water control at the transitions. The code requirements for both roofs and walls support the water control layer principles in the pen test discussed previously. The roofing chapter in the code also directly mentions the parapet walls as a critical location for both roof system transition flashing and requirements for copings. While not an exhaustive list, IBC 1503.2 includes a minimum list of areas requiring roof flashing. These are summarized below: Flashing joints in copings At moisture-permeable materials At intersections with parapet walls At other penetrations through the roof plane Roof Assembly Coping The roof requirements for parapet wall copings are spread across many categories. One section specific to copings (IBC 1503.3) has a limited scope, requiring materials to be limited to "noncombustible, weatherproof materials" and be installed with a "width not less than the thickness of the parapet wall". Many other requirements in the code also apply to copings in the code, such as flashing, wind design loads, and edge securement performance. More will be discussed about copings in those sections. Roof Wind Resistance The wind resistance for low-slope commercial roof decks and roof coverings (IBC 1504.1) is required to be designed in accordance with IBC 1609.5, which ultimately leads to utilizing ASCE 7 for determining design wind loads. There are numerous updates to ASCE 7 – 2005, 2010, or 2016 – and each has its own nuance as to how it impacts roof design loads (more here about design wind loads). Because ASCE 7 is a performance standard, it is possible to use a version with higher performance requirements because designs do not need to be the minimum allowance. Parapets are a combination of wall and roof pressures. The exact height of the parapet is not factored into the roof wind uplift calculations, but if the parapet is 3' or higher, the perimeter values can be used at the corners, lowering the uplift requirements for that portion of the roof area. Parapets can help reduce wind uplift at the corners and perimeter Roof Edge Securement Securing the edges on low-slope roofs (IBC 1504.5) has a significant impact on preventing failure and allowing the roof system to resist loads as it was designed. In addition to designing the wind resistance performance for the entire building (i.e., walls, roofs, and parapets) per ASCE 7, metal roof edges are required to be tested for resistance in accordance with Test Methods RE-1, RE-2 and RE-3 of ANSI/SPRI ES-1. The referenced standard ANSI/SPRI ES-1 is a performance requirement that is specific to the strength of metal roof edges (more here about roof edge performance compliance). ES-1 covers the "baseline" flush roof edge as well as parapet coping caps. When designing, it is important to specify compliance with ES-1 in the construction documents. Roof Coverings The IBC provides minimum installation criteria (IBC 1507) for various roof systems, based specifically on the attributes of that roof covering. In addition to the prescriptive criteria listed within, the IBC also mandates that "Roof coverings shall be applied in accordance with the… manufacturer's installation instructions." Generally, the content of these roof covering sections address minimum substrate requirements, minimum roof slope, ballast requirements, and relative ASTM references to material standards, such as D6878 Standard Specification for Thermoplastic Polyolefin (TPO) Based Sheet Roofing. Energy Efficiency for Parapets Generally, within the IBC it is required that a building be "designed and constructed in accordance with the International Energy Conservation Code (IECC) 1301.1.1". The IECC has both residential and commercial provisions, and the commercial provisions apply to "all buildings except for residential buildings 3 stories or less in height." The IECC is structured in a way that provides the option of either complying with the prescriptive requirements within it or by complying with the alternate ASHRAE 90.1 energy standard. Compliance Alternatives The IECC has multiple compliance paths within it, including: Either following the prescriptive requirements within the IECC or ASHRAE 90.1, or Following the performance modeling requirements of ASHRAE 90.1 Appendix G. The prescriptive options within both the IECC and the reference standard ASHRAE 90.1 primarily regulate energy use by providing lists and itemized requirements. These can be helpful when the building is straightforward and tradeoffs don't need to be made. When a building is more complex, has specific energy usage demands, or if an owner wants to demonstrate energy compliance beyond code, the performance path within ASHRAE 90.1 Appendix G is the methodology required. For example, any modeling being performed to show compliance with LEED is being performed to comply with Appendix G in ASHRAE 90.1. A growing method of compliance is whole-building design energy modeling and onsite performance testing happening in new construction. When an existing building is reroofed, the designer will most likely follow the prescriptive path to determine the amount of insulation to use. Insulation The insulation requirements in the table include both cavity and continuous insulation, but vary based on the framing material (IECC C301.1 & 90.1 Annex 1). Including continuous insulation in both the walls and roof systems of the parapet helps manage thermal bridging across the assemblies. The prescriptive tables in the energy codes dictate minimum R-Values in the roofs and walls based on the climate zone of the project site, the building use, and the framing materials of the wall and roof system. As described earlier in the thermal control discussion, the framing materials matter in the prescriptive requirements, especially when insulation is placed between framing members in parapet cavities. For more complex details like a parapet, the energy code doesn't get into separate requirements for the insulation. The codes generally require that continuous insulation be depicted in the construction documents with sufficient clarity to indicate the location, extent of the work, and show sufficient detail for continuity of the thermal control layer. Per the IECC (C103.2), insulation continuity for complex conditions should be shown in the details. Air Barrier ASHRAE 90.1 defines a Continuous Air Barrier as a "combination of interconnected materials, assemblies, and sealed joints and components which together minimize air leakage into or out of the building envelope." It's a good definition and an accurate description of what is needed to have a completed building enclosure that minimizes air leakage (IECC C402.5 & 90.1 5.4.3.1). Actual air leakage for a building is measured by pressurizing the enclosure with a set of blowers and measuring the airflow through the blowers to determine the air leakage through the enclosure being tested, on all 6 sides. Materials and assemblies used as a part of the building's continuous air barrier are generally tested by the manufacturers of those materials and systems to comply when installed in accordance with the manufacturer's instructions for that application. The ultimate goal of airtightness is whole-building performance. To help accomplish that goal, the energy code also specifies aspects of air barrier design (IECC C103.2 & 90.1 5.4.3.1.1) and installation (IECC C402.5.1.1 & 90.1 5.4.3.1.2) for continuity across joints, penetrations, and assemblies. Below is a brief summary of the design and installation requirements from ASHRAE 90.1: Air Barrier Design Components, Joints and Penetrations details Extending over all surfaces, including the roof Resist pressures from wind, mechanical, stack effect Air Barrier Installation Junctions between walls and roofs or ceilings Penetrations at roofs, walls, and floors Joints, seams, and connections between planes In accordance with the manufacturer's instructions Code Summary For the various applicable codes and standards, in both roofs and walls, weather protection and flashing are important requirements at all transitions and penetrations, including parapet conditions. It is vital to specify key reference standards for wind and edge securement, in order to achieve the performance needed to keep the roof on the building as intended. In general, the energy codes require continuity of the thermal and air control layers. Detailing the thermal control and air barriers to be continuous in the design AND field installation are critical for energy code compliance. For more information on parapet and control layer continuity, register for the Continuing Education Center webinar, Parapet Predicaments and Roof Edge Conundrums, sponsored by GAF and presented by Jennifer Keegan, AAIA and Benjamin Meyer, AIA, LEED AP. For more information on parapet and control layer continuity, read the Continuing Education Center article, Parapets—Continuity of Control Layers, sponsored by GAF and written by Benjamin Meyer, AIA, LEED AP.

By Authors Benjamin Meyer

January 24, 2020

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