The Growth of Green Roof Construction
Green roofs (often referred to as “Vegetative Roofs”) are roof systems that are created by adding layers of plants and growing media on top of traditional roofing systems. They have become popular as many business owners and communities become increasing more environmentally aware.
While “going green” is considered a new concept, in reality green construction and green roofs were present as early as the sixth century BC, in Mesopotamia. The hanging gardens of Babylon included raised terraces that were covered with grasses, trees, and gardens. Archeological evidence from Ireland and Scotland indicate green roofs, in the form of sod, were commonplace since the 4th century AD. Early American settlers built their homes from sod, stacked upon each other to form walls, and then mounded over to crate sod roofs.
While green roofs can be found in America, such as Rockefeller Center in the early 1930s, it was not to until the early 70s when green roofing began to be commonplace in Germany and Switzerland. By the mid 80s, Green roofs were commonplace throughout Europe. In the last several years, a renewed interest in protecting the environment and improving living conditions spurned an increase interest in green roofs.
Green roofs are not only effective in reducing stormwater runoff, improving air quality, and reducing urban heating effect; they can provide reduced heating and cooling costs for property owners. Rooftop vegetation provides insulation that reduces the amount of heat that penetrates into the roof space. Additionally, the retained moisture in rooftop soils acts as an evaporative cooling system in warm climates. All of which has made the interest in this construction technique markedly increased.
Green roof design, construction, and vegetative cover will vary depending on the roof type, roof slope, roof accessibly, and the climate. This report provides an overview of green roof technology and provides insight into concerns related to this construction technique.
Types of Green Roofs
In general, green roof types are divided into three broad categories: extensive, semi-intensive, and intensive. The key difference in each of these is the depth of the growing medium and the degree of intended roof access.
Extensive roof systems. These are the most common form of vegetative roof. Often referred to as shallow depth, these roofs typically have a soil depth of between 3 and 6 in (7.6 and 15.2 cm), which reduces the amount of water that can be retained by the system. Extensive roofs normally will utilize low maintenance plants that have strong horizontal root systems, are resistant to drought, and survive in wide temperature extremes, such as grasses or sedum. Typically, this roof design requires less structural support, is the least costly to install and maintain, and is not intended for public access.
Intensive roofs. Here, there is typically a soil depth of between 10 and 48 in (25.4 and 121.9 cm). Intensive roof systems utilize a wider variety of vegetation than that found in extensive systems and often include large shrubs and trees. In some cases, roofs will have recessed plant wells or planter boxes to allow for vertical root growth of trees. As such, intensive roofs take on the appearance of a park or garden setting, and are maintained in a similar fashion. These roofs typically have regular public access and as such may include walking paths, benches, tables, and small recreation areas (i.e., chess tables, bocce balls, etc.). Intensive roofs require a much more complex supporting structure, and as such, they are the most expensive form of green roof.
Components of a Green Roof
All green roofs have a layered structure built upon a roofing base structure. The layered structure may be built on site or arrive at the site in preconstructed modules, which are raised to the rooftop and joined together.
Basic green roof components include the base roof deck, water proofing layer, and green roof systems. The following is a summary of the basic green roof system components.
Structural deck. All green roofs are built upon a roof deck and may be made from concrete, steel, or wood. They may be flat or sloped. Much of the design of the roof system will be dependent on the amount of load the roof structure (deck) can carry. When a vegetative roof is installed on an existing roof, attention must be given to the loads that the roof can bear. Existing roofs often do not have the weight-bearing capacity to carry the heavy loads from intensive roofs. Thus, extensive roof systems are ideal for retrofitting existing roofs. For example, a conventional ballasted roof (i.e., gravel) is roughly the same weight, 15 to 30 lbs/ft2 (73 to 146 kg/m2) as a extensive green roof using lightweight soil media.
Waterproofing layer. All green roofs will have a waterproof membrane directly above the roof decking to deflect water and prevent vapor intrusion. This layer is designed as the final barrier to water intrusion, and as such proper installation is critical to prevent property loss. Membranes may be made from any number of materials including hot-fluid-applied rubberized asphalt; atactic polypropylene (APP), or styrene butadiene styrene (SBS) modified bitumen sheets; ethylene propylene diene monomer (EPDM) rubber sheets; Polyvinyl chloride (PVC); or several other blended polymer designs. Membranes may be field formed membranes that are monolithic in nature or factory-fabricated sheets, which are assembled and seamed in the field. These membranes may be either loose laid or fully adhered.
Loose laid membranes allow for more imperfections in the overlay material, but are subject to movement. The National Roofing Contractors Association (NRCA) recommends that, regardless of how the membrane is manufactured (e.g., field or factory), all membranes should be fully adhered to the overlay board. Full adhesion also is critical in actually locating leaks. When damaged, water can pool and move from place to place under non-adhered membranes, making a leak very hard to isolate.
Green roof system. Green roof system components found above the waterproofing layer include insulation, membrane protection, root barrier, growing media (overburden), and vegetative cover. Additional components can be added based on the specific design of the roof. The order in which the components are assembled will depend on the environment in which the roof is installed; the type of vegetation used; and the structural loading present. Extensive roof designs may have very few layers, while intensive designs may have multiple water retention and drainage layers to address the more complex root structure.
- Protection layer. The protection layer is designed to protect the membrane surface from damage that can occur while the remaining roof components are being installed. When walking paths, sitting areas, and similar public access amenities are provided, they are usually set on a series of pavers or bricks. The protection layer acts as a buffer between these pavers and the membrane to prevent damage form paver movement or repeated compacting from heavy foot traffic.
Any number of materials can be found in protection layers, depending on the membrane type. Typical protection layer materials include asphalt boards, extruded polystyrene (XPS) boards, and PVC. The protection layer is normally installed in 4 x 8 sheets of material ranging from 1/8 to ¼ in (3.2 to 6.3 mm) in thickness.
- Root barrier. As the name implies, a root barrier is design to halt vertical root travel and protect the waterproof membrane from damage. While the root barrier is usually a separate layer installed on top of the protection layer, it can be an integral part of the protection layer in some cases. Any number of materials can be used for the root barrier, depending on the membrane type. Typical root barrier materials include polystyrene sheets, high-density polyethylene (HDPE) of an asphalt bitumen membrane. Root barriers should have heat-welded seams to prevent root intrusion between sheets and allow for uniform expansion and contraction.
- Insulation. In some cases, an insulation layer may be added to the green roof assembly. When insulation is added to the topside of the roof, it should be designed for moist or damp environments and have a high resistance to compression. Materials used for above roof insulation can include polystyrene, closed cell foam, etc. The NRCA recommends using XPS insulation as the primary insulating means for green roofs, allowing XPS to be used as filler mixed in the top layer. Using XPS in this manner will aid in water retention without an increase the overall soil weight of the layer.
- Drainage layer. Proper drainage is critical to the overall life expectancy of a green roof. If too little water is retained in the roof assembly, the vegetation will wither and die. If too much water is retained, the gross weight of the roof can cause extensive deflection, or possibly collapse. Drainage systems typically use one of two designs, drainage mats or insulating drainage panels.
Drainage mats are honeycombed polyethylene mats, with a filter material laminated to the surface. The filter media is deigned to allow water to permeate, while retaining the soil. Drainage mats must be resistant to compression, from both the soil and foot traffic. Additionally, drainage mats should be selected based on the total volume of water expected and the retention level desired. The mats should be installed in conjunction with the drainage systems (i.e., bowels and pipes) to ensure that proper flows can be achieved.
Insulating drainage panels are flat, high-density insulation panels that have grooves running the length of the panel. The panels have a filter material laminated to the surface to allow water to permeate, while retaining the soil. Like drainage mats, drainage panels should be installed in conjunction with the drainage systems, (i.e., bowels and pipes) to ensure that proper flows can be achieved.
In the case of sloped roofs, drainage occurs naturally due to gravity and as such, drainage mats are not typically used. Rather, a gravel perimeter on the roof acts as a conduit to direct excess water to standard rain gutters.
- Growth medium (soil). Green roofs use a blend-growing medium, which contains much more than just soil. Depending on the type of vegetation and the climates, growing mediums can include a blend of small gravel, lava rock, synthetic fibers, crushed shale, bark, peat, and earth. The growing medium should be blended to provide the necessary water retention ability, resist compacting, and remain light enough to be applied to the roof area. Mesh fabric is often layered over the growing medium during the initial installation process to reduce wind borne loss of product.
- Vegetation. As previously discussed, the type of vegetation used will depend on the roof design and the climate in which it is installed. Selected plants should be suited for the growing environment and have roots systems that survive well in horizontal growth conditions. Plant, shrubs, and trees, should be suited for windy environment, with sturdy trunks and branches.
- Accessories. In addition to the components of the green roof, there may be a number of accessory items installed to augment the functionality of the rooftop, provide for maintenance efforts, or provide public amenities. Accessories can include access boxes for water valves, electrical outlets, and roof drains; irrigation systems; maintenance lockers; dividers; and walking path, benches, and lighting.
Access boxes are usually a sealed unit, with a hinged door that can be opened by hand. In the case of an intensive roof with deep soil levels, these boxes may have extensions to bring the opening to the surface of the soil. The boxes are usually designed to blend in to the green roof environment, often by being disguised as rocks.
- Fall protection. The general contractor should develop a fall protection plan that describes the fall hazards on this job and establish procedures that are to be followed in order to prevent falls to lower levels or through holes and openings in walking/working surfaces. All workers must adhere to the plan. Fall prevention systems, such as guardrails, rather than fall protection systems, such as safety nets or fall arrest devices, provide more positive means to protect workers during the construction of a green roof.
If a railing is not installed, a minimum number of workers should work for the time necessary to actually accomplish the job of leading edge work. When working less than six (6) ft from an unprotected edge, the crew is required to be tied off at all times or have guardrails installed. Workers engaged in these activities but who are more than six (6) ft from an unprotected edge, as defined by the control zone lines, do not require fall protection but a warning line or control lines must be erected to remind the crew that they are approaching an area where fall protection is required.
Likewise, the property owner should develop controls to protect maintenance workers from fall hazards. These controls may include fall prevention or fall protection devices depending on the work environment and height of roof abutments.
See Construction Management Report CM-75-00, Fall Protection in Construction, for additional information.
- General lawn care hazards. For lawn care workers, an assessment of exposures to injuries and illnesses should focus on strains, falls, machinery, hazardous substances, and general hazards. However, in analyzing the level of safety for any organization, consideration should be given to management’s concern and actions in establishing safe work procedures, and worker involvement in creating a safe work environment. A variety of chemicals, such as fertilizers, pesticides, insecticides, fungicides, herbicides, or other chemicals, may be used that are toxic to individuals, causing either acute or chronic reactions. Some chemicals will cause harm when inhaled, others when in direct skin contact. To ensure worker safety, management should establish frequent training covering chemical hazards, precautions, use of PPE, and proper sanitary methods to reduce the exposure.
Workers may suffer illnesses and injuries caused by contact with insects (e.g., spiders, scorpions, black flies, mosquitoes, ticks, bees, wasps, etc.) and animals (e.g., snakes, wild animals, dogs, etc). Workers should be advised to avoid using scented colognes, after-shave lotion, shampoos, and other personal hygiene products that may attract insects and animals.
Workers should also be advised to wear light-colored clothing to allow for easy detection of insects, and to wear long-sleeve shirts and tuck pants into boot tops or socks. Management should consider hiring a professional exterminator to clean out discovered insect nests before work continues.
See the Workers’ Compensation Exposure Controls Section of Business Link Report BL-20-27, Lawn Care Services, for additional information.
- Fall protection. Precautions to protect visitors at a rooftop equipped with green roof design should address typical walking/working surfaces protection with special consideration for egress. Risk control efforts should address protecting visitors from the roof edge. Two methods of protection are creating physical barriers or restricting access. A physical barrier can be a guardrail. Guardrails or railing systems are used in green roof applications to reduce the hazard of falling from a rooftop. The guardrail system should be designed in accordance with local building codes. If the guardrail system is a permanent fixture, then add warning signs to the railings that remind rooftop visitors to respect the boundaries. For example, a sign stating, “DO NOT LEAN AGAINST OR OVER THE BALCONY RAILING,” clearly informs visitors to stay off the rail. Railing systems should not be installed without engineering specifications that account for the potential for damaging the roof structure.
It cannot be assumed that rooftop visitors will respect implied rooftop boundaries and walk only where the design plan anticipates. The consideration for roof access and walking surfaces is essential for green roof applications when public rooftop access is permitted. The architectural design must adhere to the life safety code. Access must be restricted so that persons cannot accidentally walk near skylights, pipes, fixed machinery, equipment, etc. The path of egress must meet life safety requirements and alternative exit paths must be accessible. The exit access paths and exits should be free of debris and equipment to allow unobstructed egress travel from the rooftop to the street level in accordance with the life safety code.
Some property owners install green roofs that will not be open to the public. Even if regular visitors are not anticipated, protecting service technicians and others who access the finished roof is essential. Equipment, service, and maintenance operations should not be performed within ten feet from the edge of the green roof. If work must be performed closer to the edge, then the property owner is responsible for providing anchors for fall protection equipment. Rooftop maintenance programs will need to incorporate inspection and repair as necessary to reduce the chance of loss.
- Security. It is essential to restrict access to the rooftop during construction. The roof access restrictions should include protecting any openings in the building envelope as well as staircases and exit paths. Consider that skylights or other openings could be used to access the rooftop by uninvited visitors. Adding mounted cameras to record rooftop activity is another security measure. Security controls can be modified to include the necessary patrol activities during and after the green roof installation. For example, the security detail responsible for monitoring the parking areas can be assigned to make rounds that include rooftop observation. Ongoing communication regarding safe access, coordination of services and documentation of activity is essential.
If there will be rooftop access once the construction phase is completed, then the property owner must consider hours of operation, lighting, and security precautions to protect the public. It is unusual for a green roof project to be designed without goals to reduce energy use, conserve water resources, and provide a comfortable environment. If the hours of operation extend past daylight, then rooftop artificial lighting must be provided. This can lead to conflicts if the property owner is seeking certain energy efficiency or certification requirements. The need for energy conservation, protection of rooftop visitors, and adequate lighting requires planning and communication during the project. If it is overlooked, lighting should be installed after discussion with the roofing contractor in order to maintain the integrity of the roof.
- Other hazards. The hazards of green roofs include the need to restrict access to sheds that contain tools, gardening products, or equipment. These should be stored under lock and key. Even though most vegetative roofs take advantage of low maintenance plantings, some activities, such as treating for pests, is required. Posting notices in advance that the treatments will take place, cordoning off areas that have been treated, or restricting access to the roof until it is safe for visitors to use the roof will protect the property and any visitors.
Codes and Standards for Green Roofs
A number of different organizations provide information and recommendations on green roof design. This section identifies key organizations.
ASTM International. Subcommittee E60.01 on Buildings and Construction has developed five standards related to green roofs, including ASTM E2400, Standard Guide for Selection, Installation, and Maintenance of Plants for Green Roof Systems. The committee is also working on a guide for green roof systems. The ASTM standards can be purchased directly from the ASTM Website.
FLL. The FLL is the German Research Society for Landscape Development and Landscape Design (Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau e.V.). The FLL Guideline for the Planning, Execution, and Upkeep of Green-Roof Sites is one of the most comprehensive guides available for green roof design, installation, and care. The guide provides in-depth recommendations for all of the components of a green roof system, including the selection of vegetations and growing medium.
The FLL Guideline for the Planning, Execution, and Upkeep of Green-Roof Sites can be purchased directly from the FLL. However, the English edition of the guideline is available from several publishers in the United States.
FM Global. FM Global’s Engineering Standards Group publishes a data sheet 1-35 on green roof systems. The data sheet was first published in 2006 and provides requirements for the location, construction, operation, and maintenance of green roof systems. FM Approvals is developing an approval standard for green roofing systems. The standard, FM Global: Approval Standard for Vegetative Roof Systems Class Number 4477, is currently in draft form.
International Codes Council (ICC) Prior to 2007, the International Code series had only minimal requirements that were specific to green roofs and roof designs (e.g., Chapter 16 of the 2006 International Building Code had structural requirements for special purpose roofs, including roof gardens). Because of this, green roofs had to be approved on a case-by-case basis using provisions related to alternative means, designs, and methods of construction. During the 2006-2007 code development cycles, there were several code change proposals that were accepted for the 2009 edition of the International Building Code.
In 2009, the ICC adopted changes to the next revision of the International Fire Code (IFC) that are specific to green roofs. The proposed additions to the IFC include a new Section 316 Landscaped Roofs and Roof Gardens, which established fire safety requirements for green roofs. These requirements include limitations to the size of rooftop gardens, minimum separations between vegetative areas, and requirements for supplemental irrigation of roof vegetation to ensure proper hydration of plants. The full report of actions taken on proposal for the 2012 revision of the ICC Codes can be accessed, via the ICC Website.
National Roofing Contractors Association (NRCA). The NRCA provides design recommendations for green roofs, as well as all other roof types. The NRCA is one of the oldest construction trade organizations in the United States. The NRCA “Vegetative Roof Systems Manual” provides a review of the technologies available for vegetative roof systems, including the waterproofing systems, protection layers, root barriers, drainage layers, insulations, and growing mediums. The manual can be ordered from the NRCA Website.
Single Ply Roofing Institute (SPRI). On January 29, 2010, the Single Ply Roofing Institute standard VF-1, the External Fire Design Standard for Vegetative Roofs was approved as an American National Standard by ANSI. The standard was developed in conjunction with Green Roofs for Healthy Cities and provides a method for designing external fire resistance for vegetative roofing systems. It references the FLL and FM Global standards. A second standard, RP-14, covering wind uplift, was not approved and will be reballoted.
Risk Control in Green Roof Construction
Collapse. Green roofs add both static and dynamic weight to a structure. The static weight added is the composite total of the added layers placed above the roof deck. Dynamic loading comes from the retained water on the roof and any loading caused by public access. When new roofs are designed, the supporting roof structure is designed to address these loads. However, when a green roof is added to an existing roof deck, it is imperative that a structural engineer evaluate the roof to determine what, if any, additional load the roof will bear.
Extensive roofs are the most common green roof found. When a green roof is added to an existing structure, it is normally an extensive roof system, due to the reduced weight of the design. Extensive roofs typically have a weight of 15 to 30 lb/ft2 (73 to 146 kg/m2), including retained water, which is comparable to the weight of gravel on a ballasted roof. Semi-intensive roofs typically have a weight of 30 to 60 lb/ft2 (146 to 290 kg/m2). Intensive roofs typically have a weight of 60 to 200 lb/ft2 (290 to 967 kg/m2). Designers need to calculate total roof loading based on these weights, any accessories, and retained water at super-saturation. Super-saturation is used as the water retention weight to address accidental blockage of roof drains or heavier than normal rainfalls and melting snow loads.
Care should be taken to avoid altering the static loading of the roof. Changing soil or plant type or adding accessories, such as benches and tables, can significantly alter the weight of a green roof and lead to over compression of drainage layers, membranes, and deflection of the deck. In severe cases, excessive loading can result in total roof support failure. Likewise, the dynamic loading of a roof must be closely monitored. Roofs should be designed to carry the static load of the roof plus loading created by retained water, snow, and public traffic. During periods of unusual snowfalls, it is critical that the roof structure be inspected for excessive deflection. Facilities should have a contingency plan to remove heavy snowfalls from roofs to avoid overloading. Likewise, altering the estimated human load, such as hosting an outdoor party for staff on the roof, for a roof can lead to a failure of the system.
Water instrusion. Leaks in the waterproofing system are most often caused by damage during installation of the membrane or the protection course. Roof membranes can be easily damaged by foot traffic and moving materials across the surface of the roof. Careful coordination of the project is necessary to ensure that the roof membrane is adhered, sealed, and cured before the protection layer is installed. Likewise, an excessive lapse in time between applying the membrane and insulating the protection layer can lead to damage to the membrane from windborne debris, human contact, and sun damage.
It should be noted that the National Roofing Contractors Association (NRCA) does not support the dryness testing process referenced in ASTM 5295, Standard Guide for Preparation of Concrete Surfaces for Adhered (Bonded) Membrane Waterproofing Systems, published by the ASTM International (ASTM). Rather the NRCA recommends that a small piece of membrane be adhered to a test location, allowing it to cure, and then attempting to remove it. The NRCA believes that this testing process provides a more reliable assessment of not only moisture, but also of the presence of surface containments, such as oil, that could impede adhesion.
The waterproof membrane is normally not applied directly to a metal or wood deck roof. These roof decks should have moisture-resistive gypsum (i.e., green board) or cementations (i.e., Hardi board) overlay board attached to the top surface to provide a surface for the waterproofing membrane to be adhered to. Overlay boards should be a minimum of 5/8-in (1.56-cm) thick. In some cases, such as lighter extensive wood roofs, marine-grade plywood may be used, particularly in the case of sloped roofs.
Incorrect sealing of joints and roof edges also can lead to leakage. Failure to properly seal penetrations in the membrane, such as for vent pipes, is a significant concern for water intrusion. Many installers recommend flood testing the roof before applying the protection layer. Flood testing requires sealing roof drains and applying a shallow layer of water over the entire roof surface. The underside of the roof deck is then examined for leaks. If no leaks are found, the roof is drained and the protection layer is installed. Other contractors employ electronic leak detection methods; eddy current leakage is detected at pinholes in roof coverings.
Roof anchorage. Barring structural loading concerns, any roof can be vegetative. However, as the slope of a roof increases, so too does the threat of vegetative assembly sliding from the roof. Low or no slope roofs, up to a 10-degree pitch can be installed without the need for any additional anchoring, other than what is found in a flat roof system.
Roofs with slopes greater than 10 degrees and up to 30 degrees, will require additional anchoring. This anchoring can include any combination of lath grids, ridged mesh that the system is attached to, or an eave-mounted support that prevents the assembly from sliding. Roofs with a pitch greater than 30 degrees require substantial efforts to secure the system to the roof. These systems create smaller roof surface, which increases the friction to surface ratio. This gridded type of system prevents the weight of the highest vegetation layer from adding force to the layers closest to the roof edge. In many cases, these systems are actually comprised of a series of shallow boxes in which the system is installed. Modular-designed roof systems require additional care during installation to ensure that the modules are anchored to each other and that the entire system is properly weighted to avoid wind uplift.
Roofs with a slope greater than 30 degrees warrant the use of pre-grown mats, which are fastened to the protection barrier. However, the installation and maintenance costs of this type system is often cost-prohibitive. For that reason, steep roofs are rarely designed to be a vegetative-style roof.
Benches and tables located on intensive roofs should be lightweight and tethered to the roof structure to avoid wind uplift exposures. In many cases, these benches will be placed in areas where the growing medium has been cleared and walking paths installed.
To separate green areas from paths, skylights, and roof edges, divides are installed; these dividers act as a wall between the green space and the open space. Dividers are normally L- shaped metal or plastic brackets that are attached to the protection layer and extend to just above the soil level. These dividers also must be secured to prevent strong winds from displacing them.
Fire. Fire safety for green roofs should be focused on protecting the roof from exposure fires, limiting the ability for fire to travel on the roof; and ensuring the vegetative matter does not act a fuel source. To limit fire travel on a roof, the roof vegetative cover should be limited to not more than 15,625 ft2 (1,450 m2). Additionally these areas should not have any dimension that exceeds 125 ft (39 m). Larger roof surfaces should be divided into smaller growing areas to maintain the maximum size. Growing areas, spaces adjacent to vertical walls, and combustible roof surfaces should be separated by at least a 6-ft (1.8-m) clear space, with a Class A flame spread rating.
Vegetative cover should be selected based on their growing properties and the environment in which they are to be placed. Plants that can survive for longer periods without watering are normally preferred. Routine irrigation of the plant life to maintain healthy growth is imperative to reduce the likelihood of vegetation becoming a fuel source. The roof area should be equipped with fire suppression equipment, such as a smaller fire hose, to combat vegetative fires. In areas subject to wild fires, a prevention plan should be in place to pre-wet the roof with water or water and fire retardant foam, in advance of approaching fires. Smoking should be prohibited on rooftops, and access to chemical storage and lawn care equipment should be restricted.
Wind. Windborne debris can be a concern in high wind areas, especially while a new roof is growing in. Material can be scoured from the roof and become a hazard to both the structure itself and to surrounding areas. The use of modular systems or pre-established vegetation mats can reduce potential exposures of new roofs.
Rooftop maintenance programs will need to incorporate inspection and repair as necessary to reduce the chance of loss. As part of the inspection process, all locations where the roof membrane is exposed to the environment should be checked for adhesion. A loose piece of membrane on a parapet wall can easily become a sail in a high wind, allowing air to create uplift in the membrane.
Benches, planters, and similar accessories should be securely attached to the rooftop using anchors that are designed to withstand high winds. Particular attention should be given to routine maintenance operations, clearing of deadfall, and other debris from the roof area. Grass clipping, branches, and similar waste vegetation should not be permitted to sit on the rooftop. A disposal process should be included in the roof care process.
Special consideration should be given to the timely removal of construction debris. Workers must follow plans for debris removal during the construction phase. For areas subject to routine windy conditions, installing safety netting to protect those below the work area from falling objects may be necessary. See Construction Management Report CM-75-01, Fall Management – Personnel & Debris, for additional information.
Occupational safety. While the occupational hazards related to green roof operations are often assessed into two distinct categories: construction hazards and maintenance hazards, the controls in many cases are more focused on the exposure and not the job classification. Fall protection is a primary concern for both construction workers and maintenance personnel. Likewise, both construction (i.e., green roof installers) and maintenance workers are exposed to hazards that mimic those of a lawn care worker.
Hazards to the public. A number of distinct concerns to public safety are present for green roof property owners, including fall protection, falling debris, and security of the premises. If the roof is open to the public after construction then roof access, hours of operation, walking surfaces, and lighting are additional hazards to public safety.
Contractual risk transfer. Green building or green roof project claims typically occur because of contractual disagreements. Three hazards in contracts as they relate to green roof projects are project delays, penalties, and handling of disputes. It is important to review these items for green roof projects in addition to the traditional contractual risk transfer clauses in agreements as they relate to insurability. It is essential that agreements include maintenance provisions for green roofs. Traditional construction agreements often include terms and conditions regarding timeframes or delay penalties. These clauses, if not modified for a green roof project, could result in disputes. Contracts should provide a method for resolving disputes.
For more information on loss control and managing business risks, check out the American Family Insurance Loss Control Resource Center.
1. Bonda, Penny and Sosnowchik, Katie. Sustainable Commercial Interiors. Hoboken, NJ: John Wiley & Sons, 2007.
2. Factory Mutual Engineering Corp. Green Roof Systems. Loss Prevention Data Sheet 1-35. Norwood, MA: FM Global, 2007.
3. Hartwig, Robert. The Insurance Economics of “Going Green”; Insurance at the Vanguard. Insurance Information Institute. 9 December 2009.
4. International Codes Council (ICC). International Fire Code (IFC). 2009 ed. Falls Church, VA: ICC, 2009.
5. Matt, Chris. Five Minutes With… Maintenance Management Magazine. Strategies for Specifying Green Roofs with Tim Pennigar. Duke, NC. 5 March 2009.
6. Morton, Steve. “The Business Case for Green Design.” Building Operations Management. November 2002.
7. National Roofing Contractors Association. Green Roof Systems Manual. 2007 ed. Rosemont, IL: NRCA, 2007
8. Single Ply Roofing Industry (SPRI), External Fire Design Standard for Vegetative Roofs. ANSI/SPRI VF-1. 2010 ed. Waltham, MA: SPRI, 2010
9. U.S. Department of Energy. “Federal Technology Alert, Green Roofs”. DOE/EE-0298. Government Printing Office, Washington, DC. 2008.
COPYRIGHT ©2010, ISO Services, Inc.
The information contained in this publication was obtained from sources believed to be reliable. ISO Services, Inc., its companies and employees make no guarantee of results and assume no liability in connection with either the information herein contained or the safety suggestions herein made. Moreover, it cannot be assumed that every acceptable safety procedure is contained herein or that abnormal or unusual circumstances may not warrant or require further or additional procedure.