RACKING AND ATTACHMENT CRITERIA FOR EFFECTIVE MEMBRANE ROOF SYSTEM INTEGRATION Public Version 1: July 9, 2012 Commercial rooftops represent the most available, sustainable and secure real estate for new solar energy Approximately 3 billion square feet of new roofs are installed on existing and new buildings in the United States each year. At a 50 percent utilization rate, the solar energy industry could leverage this rooftop space to add 5 gigawatts of photovoltaic capacity annually. In order to accelerate the deployment of properly installed, well- maintained solar energy roofing systems, the Center for Environmental Innovation in Roofing (Center) launched the Center PV Taskforce in October 2011. The Center PV Taskforce works to bridge the gap and increase communication between the roofing and solar industries. The Center PV Taskforce is publishing the first public version of PV Racking and Attachment Criteria for Effective Membrane Roof System Integration to address the critical interaction between the solar racking system and roofing system. The criteria document identifies five fundamental principles of effective roof system integration: A. External Forces B. System Integration C. Roof Drainage D. Roof and PV System Maintenance E. Roof Safety Each fundamental principle is parceled into specific examples and recommended action items. The Center PV Taskforce intends PV Racking and Attachment Criteria for Effective Membrane Roof System Integration to provide a guide to the practitioner for the design, installation and long- term maintenance of rooftop solar racking Questions/Comments Please send questions or comments regarding the document to the Center PV Taskforce by email at PVTaskforce@RoofingCenter.org, or by telephone at 202.380.3371.
Table of Contents A. External Forces...3 B. System Integration...5 C. Roof Drainage...8 D. Roof and PV System Management...9 E. Roof Safety...11 Page 2 of 11 Center PV Taskforce
Fundamental Principle A: External Forces FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO A.1. Base mounts of ballasted and self- ballasting racks may puncture, cut or abrade the roof waterproofing surface through vibration, creep or expansion / contraction. A.1.a. Include durable protection layer(s) of compatible materials between all ballasting materials and the roofing surface. Protection layer(s) shall be designed to prevent damage to the roofing membrane over the service life of the PV / roofing system. If approved by the roof system manufacturer, protection layer(s) may be directly integrated into the ballasted racking system. A. EXTERNAL FORCES. The racking and attachment system shall be designed so that external forces acting on the rack do not compromise roof waterproofing integrity. All vertical and horizontal forces should be transferred to the building structure without overloading or damaging the roofing system. Loads to be considered include wind loads, wind uplift loads, dead loads, snow loads, seismic loads as well as thermal expansion / contraction and non- specific vibratory loads from external forces or building equipment. A.2. Base mounts of mechanically attached racking systems may move laterally under load due to external forces or internal expansion / contraction, causing distortion and failure of flashing and sealing materials. A.1.b. Include expansion / contraction joints in the racking system and/or racking mounts to minimize differential movement between the roofing and racking system. A.2.a. Whenever possible, anchor the racking system directly to the building structure or structural blocking. When anchoring to the roof deck, the roof deck shall be capable of accommodating the imposed loads or reinforced with adequate blocking. In all cases, the attachment method shall provide adequate uplift/pullout resistance and resistance to lateral loads. A.2.b. Racking mounts and roof flashing details shall be designed so that lateral racking movement is accommodated without damaging the integrity of roof flashings. This may be accomplished through the use of flexible roof flashing details and materials that accommodate lateral movement of the racking mounts as well as minimization of movement of the racking mounts. Calculation of loads and sizing of base mount surface area shall be in accordance with the most recent edition of ASCE 7 and in consideration of the physical properties of the flashing materials. Ballasted and other non- mechanically attached PV racking Mechanically attached PV racking Mechanically attached PV racking systems and ballasted racking anchors. Page 3 of 11 Center PV Taskforce
FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO A.3.a. Use integrated PV and roofing systems documented for compatibility by the respective PV and roofing system manufacturers. A.3. PV systems that are fully adhered to a mechanically attached roof surface may exert stresses within the adhesives that could disbond the PV modules or alter the uplift resistance of the mechanically attached roof system. A.4. Base mounts of ballasted and other non- mechanically attached racks may overload the underlying roof surface area, causing puncture or permanent compression of the roofing system. A.5. Large arrays of sloped PV modules and racking systems may cause drifting snow build- up and possibly overload portions of the roof. A.3.b. Use integrated PV / roofing systems that have been certified for code- compliant wind uplift resistance, either through recognized third- party testing (UL, FM or equal) or an engineering analysis prepared by a licensed Professional Engineer. A.4.a. Use base mounts of sufficient surface area to distribute vertical loads without cutting or compressing the underlying roofing system. Calculation of loads and sizing of base mount surface area shall be in accordance with the most recent edition of ASCE 7 and in consideration of the compressive strength and puncture resistance of the underlying roof system components. A.4.b. Install high- density cover board beneath roofing membrane and above thermal insulation to reduce the likelihood of compression of underlying insulation. A.5.a. In areas where snow occurs, a structural analysis shall be performed by a licensed Professional Engineer to account for possible snow drift build- up in accordance with the most recent edition of ASCE- 7. In addition, consideration shall be given for large horizontal racking components, such as covered wireways and wind deflectors. PV systems directly adhered to mechanically attached roofing Ballasted and other non- mechanically attached PV racking Page 4 of 11 Center PV Taskforce
Fundamental Principle B: System Integration FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO B.1. Ballasting materials such as concrete pavers may deteriorate, causing increased racking movement and puncture of the roof surface. B.1.a. Use ballast pavers or other ballasting materials that have been documented for long- term durability. B. SYSTEM INTEGRATION. The components of the racking system and roofing system shall be designed for compatibility and documented to prevent or mitigate premature failure that could compromise roof waterproofing integrity. B.2. Ballasting materials installed directly over roofing systems with mechanical fasteners located directly beneath the roofing membrane may cut or puncture the roofing membrane. B.3. Ballasting materials installed directly over mechanically attached racking anchors may cut or puncture the roofing membrane. B.4. Racking and roofing system components with a service life less than either the PV system or underlying roofing system may deteriorate and compromise overall system performance and service life. B.1.b. Use racking trays / holders designed to contain deteriorated and cracked pavers. B.2.a. Avoid installing ballasted and self- ballasting racking systems over roofing systems containing mechanical fasteners directly beneath the roofing membrane. Examples of such roofing systems include mechanically attached membrane systems and fully adhered membrane systems with insulation fasteners directly beneath the roofing membrane. Alternatives to installing ballasted and self- ballasting racking systems over such roofing systems include the use of mechanically attached PV racking systems and / or the use of fully adhered roofing systems using one or more layers of adhered insulation or cover board directly beneath the roofing membrane. B.3.a. Avoid installing any ballasting materials directly over mechanically attached racking anchors. B.4.a. Use racking and roofing system components fabricated from materials that will provide an expected service life equal to or greater than the service life of the combined PV / roofing system. Execute PV racking and roof system maintenance programs recommended by the respective manufacturers to achieve the expected length of service B.4.b. Whenever there is a reasonable expectation that the racking system or roofing system may need to be replaced prior to Ballasted and self- ballasting PV racking Ballasted and other non- mechanically attached PV racking systems installed over fully adhered or mechanically attached roofing Ballasted and other non- mechanically attached racking systems with supplementary mechanical anchors. Page 5 of 11 Center PV Taskforce
FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO the end of the useful service life of the PV system, a decommissioning / recommissioning plan shall be established. At a minimum, this plan shall include a logistical plan for removal and replacement of the racking / roofing / pv system components, a projected budget for the replacement, and a financial analysis of the effect of the replacement on project return on investment B.5. PV modules adhered directly to the roofing surface will increase the heat load on the roof membrane and adhesives which may compromise roof system performance and service life. B.6. Thin- film PV adhered directly to mechanically- attached roofing systems may billow or flutter, causing additional stresses on critical components and connections and may compromise both PV and roof system performance and service life. B.7. Flashing details not reviewed and approved by the roof system manufacturer / roof warranty issuer or not in conformance with NRCA guidelines may compromise roof system performance and service life. B.8. Base mounts with complex cross- sections may be difficult to flash and subject to premature failure and moisture penetration. B.9. The roofing system may be damaged during staging and installation of the PV system. B.5.a. Use roofing membranes and adhesives that are designed and certified by the roof system manufacturer to be compatible with the additional heat loads from PV laminates and provide a projected service life equal to or greater than the PV system. B.6.a. Consider use of a fully adhered roof system in lieu of a mechanically attached system, or restrict billowing by installing a continuous air barrier. Note: The application of thin- film PV directly adhered to existing mechanically attached roofing systems is not recommended without approval and acceptance of the roof system manufacturer. B.7.a. Use flashing details that have been reviewed and approved by the roof system manufacturer / roof warranty issuer and installed by an approved applicator. B.7.b. Use flashing details in conformance with most recent edition of NRCA guidelines. B.8.a. Whenever possible, use round or tubular base mount materials which can be flashed securely and do not require penetration pockets. B.9.a. Load and store PV system components in designated staging areas. Do not overload the roofing system or the building PV systems directly adhered to the roofing surface. (Both fully adhered and mechanically attached roofing ) PV systems directly adhered to mechanically attached roofing All PV systems installed over a new or existing roof system warranted by a roof system manufacturer or other warranty issuer. All PV systems installed over a new or existing roof system NOT warranted by a roof system manufacturer or other warranty issuer. Mechanically attached PV racking Page 6 of 11 Center PV Taskforce
FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO structure. Install protection materials between the PV system components and the roofing surface to prevent compression, abrasion, cutting or puncture. Store PV system components on raised pallets to allow roof drainage. B.9.b. Whenever possible, confine installation traffic to designated walkways covered with protection materials to prevent compression, abrasion, cutting and puncture of the roofing system. Cover the roofing system with protective materials whenever field installation may require or produce sharp objects that could cut or puncture the roofing system. Bag and remove debris from the roof on a regular basis. Page 7 of 11 Center PV Taskforce
Fundamental Principle C: Roof Drainage FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO C. ROOF DRAINAGE. The racking and attachment system shall be designed so that water drainage on the roof is not compromised. C.1. Racking systems with horizontal elements (either structural elements or wireways) that block the roof drainage plane may cause water to pond on the roof and allow for debris accumulation. C.1.a. Maintain a minimum clearance between the roof surface and any horizontal element of the racking system sufficient to allow effective roof drainage. As an alternative, the racking system shall contain drainage openings or gaps that allow adequate water flow. In all cases the drainage design of the combined PV / roof shall be based on calculations derived from the most recent edition of the International Plumbing Code. Assure that all areas where debris may accumulate are accessible for cleaning C.1.b. Whenever possible, orient the racking system so that horizontal elements blocking roof drainage are parallel to roof drainage flow. Design ballast mounts to provide drainage in both directions of the mount or to redirect water around the mount. C.2. Placement of racking systems may impede access to roof drains for periodic maintenance. C.2.a. Provide access to roof drains suitable for periodic maintenance. C.3. Roof curbs greater than 30 inches wide* supporting PV equipment such as inverter and combiner hardware may block drainage and cause water to pond on the roof. (* as measured perpendicular to the slope per most recent edition of the International Building Code.) C.3.a. Whenever possible, orient roof curbs greater than 30 inches wide* supporting PV equipment so that they provide drainage in both directions or redirect water around the curb." (* as measured perpendicular to the slope per most recent edition of the International Building Code.) Page 8 of 11 Center PV Taskforce
Fundamental Principle D: Roof and PV System Maintenance FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO D.1. The PV system may obstruct safe and effective access to rooftop equipment and other openings requiring periodic inspection and maintenance. D. ROOF and PV SYSTEM MAINTENANCE. The racking and attachment system shall be designed to allow effective roof and PV system inspection, leak detection, maintenance and repair. D.2. PV racking system components may obstruct effective observation and maintenance of underlying roof surfaces by roofing workers. D.3. In the event that major roof system repairs are needed, the PV racking system may need to be temporarily disassembled and stored to allow for roof repairs. D.4. Roof maintenance may be performed by personnel with inadequate training to service roofs with PV systems or insufficient information regarding the specific rooftop PV installation. D.1.a. Provide designated walkway areas for roof inspection and maintenance. At a minimum, roof walkways should include an unobstructed pathway along the perimeter of the roof as well as unobstructed pathways leading from all roof access points to and around all rooftop equipment and other openings that may require periodic maintenance. Walkways shall be constructed of durable and compatible materials suitable for protecting the roof surface, as approved by the roof system manufacturer or roofing contractor. In all cases, design and layout of walkways shall conform to the requirements of the most recent edition of the International Fire Code. D.2.a. Whenever possible, provide clearances between the racking system and the roof surface sufficient for effective inspection and maintenance. When sufficient clearances cannot be achieved, use racking system components that can be disassembled for inspection and maintenance. D.3.a. Staging areas for PV system disassembly and removal shall be identified and provided. (See also B.7.a.) D.4.a. Assure that roof maintenance in close proximity to the PV system is conducted by roofing personnel trained to work safely and effectively around PV components. D.4.b. Whenever possible provide the building owner with maintenance manuals covering all major elements of the roofing and PV system, including a roof system manual provided by the roof system manufacturer or roofing contractor, a PV system Page 9 of 11 Center PV Taskforce
FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO maintenance manual provided by the PV manufacturer or installer, and a racking system maintenance manual provided by the racking system manufacturer or installer. D.5. PV cleaning materials may cause premature deterioration of roof membrane. D.6. Lack of electricity and water supply on rooftop increases costs for maintaining roof and PV D.5.a. Coordinate PV maintenance guidelines to ensure compatibility between PV maintenance and roof system, especially the use cleaning chemicals that are compatible with the roof system membrane. D.6.a. Provide water and electrical utilities to roof for operation and maintenance of roof and PV system. Page 10 of 11 Center PV Taskforce
Fundamental Principle E: Roof Safety FUNDAMENTAL PRINCIPLE EXAMPLE RECOMMENDED CRITERION APPLIES TO E.1. Racking system components may impinge on designated maintenance and service walkways. E. ROOF SAFETY. The racking and attachment system shall be designed to assure worker safety during roof inspection, maintenance and repair. E.2. Racking system layout may create an unnecessary fall exposure. E.1. Whenever possible, design racking systems to allow unimpeded access along all designated walkways. In all cases, design and layout of walkways shall conform to the requirements of the most recent edition of the International Fire Code. E.2. Develop and implement a long- term fall protection plan to allow safe access to the PV system both during system installation and ongoing system maintenance. (End of Document) Page 11 of 11 Center PV Taskforce