RoofViews

Building Science

Parapets Part 2: Navigating Codes

By Benjamin Meyer

January 24, 2020

Two men on a parapet looking at their phones

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 < perm="" ≤="" 1.0="">
  • Class III: 1.0 < perm="" ≤="" 10="">

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:

  1. Either following the prescriptive requirements within the IECC or ASHRAE 90.1, or
  2. 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.


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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Likewise, The National Energy Code of Canada for Buildings: 2020 addresses thermal bridging of a number of building components, but also explicitly excludes fasteners: "in calculating the overall thermal transmittance of assemblies…fasteners need not be taken into account" (Section 3.1.1.7.3). Admittedly, point thermal bridges are often excluded because it is challenging to assess them with simple simulation tools.Despite this, researchers have had a hunch for decades that thermal bridging through the multitude of fasteners often used in roofs is in fact significant enough to warrant study. 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The continuous cleat is typically one gauge thicker than the edge metal and coping.Why is wind design of edge metal important?The roofing industry has been investigating high-wind events, primarily through a group called the Roofing Industry Committee on Weather Issues (RICOWI). RICOWI was established in 1990 and has published numerous reports based on post-wind-event investigations of damage caused by hurricanes. RICOWI's most recent report, released November 19, 2019, covers their investigation of the damage caused by Hurricane Michael. RICOWI has published five reports covering their investigations of 6 hurricanes since 2004.One of the most consistent conclusions throughout the series of 5 reports of post-event investigations is that the majority of localized roof damage and roof system failures due to high winds commonly begin at perimeters and corners. This is not surprising as the highest wind loads are at rooftop perimeters and corners. This blog about wind design and ASCE-16, among other topics, discusses the process and factors used to determine wind loads, and it provides additional information about roof zone layout. Localized roof damage and roof system failures due to high winds commonly begin at perimeters and corners. Not recognizing the importance of edge metal design relative to the overall wind performance of a roof system can result in edge metal installations that may not have the appropriate wind-resistance capacity. This could possibly result in localized damage and/or system failures, even when the roof system (i.e., deck, insulation, membrane) is appropriately designed for design wind loads.The following information is intended to supplement the wind design concepts that were discussed in GAF's earlier blog about wind design and ASCE 7-16.Roof and Wall ZonesWind design of metal edges and copings includes an upward and an outward component, unlike the primary roof system which includes an upward component only. (The Edge Metal Testing section of this blog has more information on that topic). ASCE 7 calls the outward pressures acting on metal edges and copings Wall Zones 4 and 5. Wall Zone 4 correlates and is aligned with Roof Zone 2 (the perimeter zones), and Wall Zone 5 is aligned with Roof Zone 3 (the corner zones). The figure shows one example of a building's roof and wall zones. Case studies from this blog provide more specific information related to the figure below.What do the codes say?The International Building Code (IBC) includes requirements for determining the wind-load capacity for metal edges and copings. This requirement has been included since the 2003 version of the IBC. In other words, edge metal and copings should have wind-resistance capacities greater than the design wind pressures. This concept is just like wind design for the primary roof system—the capacity of the system needs to be greater than the anticipated loads.Chapter 15, Section 1504.5 from the 2015 IBC includes requirements for determining the capacity of metal edges and copings."1504.5 Edge securement for low-slope roofs. Low-slope built-up, modified bitumen and single-ply roof system metal edge securement, except gutters, shall be designed and installed for wind loads in accordance with Chapter 16 and tested for resistance in accordance with Test Methods RE-1, RE-2 and RE-3 of ANSI/SPRI ES-1, except Vu1t wind speed shall be determined from Figure 1609A, 1609B, or 1609C as applicable."Chapter 16 of the IBC indirectly includes requirements for determining the wind loads acting on metal edges and copings. In Section 1609.1 Applications, the IBC states "Buildings, structures and parts thereof shall be designed to withstand the minimum wind loads…" The "parts thereof" encompasses metal edges and copings. The requirement in Chapter 15 to design and install metal edges and copings means the outward pressures for Wall Zones 4 and 5 need to be determined.It's worth noting that the scope of the ANSI/SPRI ES-1 test method does not include gutters, which is why gutters are specifically excluded in the code language through 2018. However, SPRI, in 2016, published ANSI/SPRI GT-1, Test Standard for Gutters, which was first included in model codes in the 2021 IBC.Edge metal testingDetermining the design wind pressures (in pounds per square foot) for Wall Zones 4 and 5 is generally the responsibility of the design professional, such as the architect or structural engineer. On the other hand, determining the capacity of metal edges and copings is generally the responsibility of the manufacturer, which may be a manufacturing company or a roofing contractor that fabricates their own metal edges, coping, and clips and cleats.The IBC specifically lists ANSI SPRI ES-1, Test Standard for Edge Systems Used with Low Slope Roofing, as the test method to be used to determine capacity for metal edges and copings. ES-1 includes three (3) test methods (RE-1, RE-2, RE-3), each for a different edge condition.The RE-1 test method is for 'dependently terminated roof membrane systems'. Essentially, a mechanically attached or ballasted membrane is considered to be dependently terminated if a "peel stop" or row of fasteners is not included within 12" from the roof edge. Without a peel stop or a row of fasteners close to the edge of the roof, the edge metal is acting as the mechanical attachment of the perimeter of the membrane. (The RE-1 figure below is rotated clockwise 115 degrees to show the as-tested configuration of the metal edge. ES-1 presumes a ballasted or mechanically attached membrane will flutter and apply load to the metal edge at 25 degrees. The rotated configuration accommodates a hanging load.)The RE-2 test method is for essentially all metal edge types as long as the "horizontal component" is 4" wide or less.The RE-3 test method is for copings, and RE-3 includes two tests. One test includes an upward load and a 'face' load; the second test includes an upward load and the 'back leg' load.The wind-resistance capacity of metal edges and copings is provided in "pounds per square foot" (psf). This is appropriate because the design wind pressures are also in PSF values which makes the comparison of design wind pressures to wind-resistance capacity simple.Where to find Approval Listings for edge metalSimilar to approval listings for roof systems, there are approval listings for metal edges and copings. Approval Listings are found on FM's RoofNav and UL's Product IQ. An account (free) is required for both. Additionally, NRCA has Approval Listings for contractor-fabricated metal edges and copings which are housed on UL's Product IQ and Intertek's Directory of Building Products.ULKnowing UL's Category Control Number is key to navigating UL's Product IQ. . For metal edges and coping, UL's Category Control Number is "TGJZ". After logging in, performing a search using "TGJZ" provides a list of the manufacturers that have Approval Listings with UL. Clicking on GAF's Approval Listings allows users to easy find rated Roof-edge Systems, Metal, for Use with Low-slope Roofing Systems.Within UL's TGJZ category, GAF has 16 metal-edge products rated using the RE-2 test method and 8 coping products rated using the RE-3 test method. For example (as shown in item 3 in the screen capture above), GAF's M-Weld Gravel Stop MB Fascia B made with aluminum is rated "190 psf". That means this product can be used when the design wind pressures, which include a safety factor, for Wall Zones 4 and 5 are less than or equal to 190 psf.FM's RoofNavWithin RoofNav, Approval Listings for metal edges and copings can be found under "Product Search" using the "Flashing" category. Most likely, users of RoofNav are familiar with the "Assembly Search" function which is regularly used to locate roof systems based on their wind-uplift ratings.The search can be further refined within "Subcategory" by selecting Expansion Joint, Gutter, or Perimeter Flashing.Currently, GAF has 59 Approval Listings in RoofNav: 12 for Coping, 41 for Fascia, and 6 for Gutter products. A screen capture from RoofNav shows GAF's first 20 products.Looking closely at the Listing, the EverGuard EZ Fascia AR – Steel provides detailed information about the product itself and the installation requirements. As shown below, the listing includes multiple Ratings (i.e., wind-uplift capacity) based on material type and thickness, and face height.While the Listing is for a steel fascia, an aluminum fascia is also shown in the detailed information. It's important to note that the chart with the "steel" listing's detailed information is the same chart that is available for EverGuard EZ Fascia AR – Aluminum, as well. Therefore, it's prudent for designers and specifiers to provide appropriate information in the specification to avoid mis-communiction about intended product use.Take note of the material and gauge of the "retainer" (i.e., the continuous cleat). The continuous cleat is required to be 0.50 aluminum, regardless of fascia material type for this Listing. Because the strength of the cleat is a significant factor to the overall wind-uplift capacity of the metal edge (or coping), increasing the thickness of the cleat proves to be an effective method to increase performance.FM RoofNav and Edge SecurementFM announced on its website on October 28, 2021 that "The Wind Ratings Calculator has been updated to return separate flashing ratings for roofs." The red-highlighted area shows the required capacity for Fascia, Coping, and Gutter products.Comparison of the Minimum Wind Uplift Approval Ratings Needed (1-75, 1-90) to the Perimeter and Corner Ratings of the EverGuard EZ Fascia shows that each product type provides the required capacity, and in most cases the required capacity greatly exceeds the required rating.Load PathThe 3 test methods included in ANSI/SPRI ES-1 standard determine the wind-resistance capacity of edge metal attached to a substrate. In other words, the measured capacity (Rating) is of the metal edge or coping attached to the wood blocking; the tests do not measure the capacity of the attachment of the wood blocking to any substrate. The National Roofing Contractors provide information on this topic. The NRCA Roofing Manual: Membrane Roof Systems—2019, on page 289 states:"Wood Nailers and Blocking: Many of the construction details illustrated in this manual depict wood nailers and blocking at roof edges and other points of roof termination. Wood nailers must be adequately fastened to the substrate below to resist uplift loads. This especially is true at parapet walls/copings and roof edges where edge-metal shapes are fastened to wood blocking.Among other advantages, the nailers provide protection for the edges of rigid board insulation and provide a substrate for anchoring flashing materials. Wood nailers should be a minimum of 2 x 6 nominal-dimension lumber. To provide an adequate base, nailers should be securely attached to a roof deck, wall and/or structural framing. In the design of specific details for a project, a designer should describe and clearly indicate the manner in which wood nailers and/or blocking should be incorporated into construction details. A designer should specify the means of attachment, as well as the fastening schedule for all wood nailers and blocking."To that end, FM Global Property Loss Prevention Data Sheet 1-49, Perimeter Flashings, provides a number of recommendations for anchoring wood blocking to various types of walls and structural framing. One example of a roof/wall intersection shows the bottom nailer bolted to the bar joists to ensure an adequate load path.In SummaryArchitects, specifiers, and roof system designers are required by code (always check specific local requirements) to determine wind loads not only for the primary roofing system, but for the metal edges and copings as well. Manufacturers and fabricators are responsible for determining the wind-uplift capacity of their metal edge and coping products, as well as their primary roofing systems.Given the relatively new requirements in the IBC for edge securement, designers, consultants, and specifiers should become familiar with both UL's and FM's approval listings for metal edges and copings. Manufacturers of metal edge and coping products are available to assist designers with selection of edge securement.

By Authors James R Kirby

April 24, 2023

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