In cities with combined storm and wastewater sewer systems, storm water dilutes the sanitary waste water, rendering treatment less efficient. They are lightweight and have a shallow build-up height. The organic matter content should be based on the manufacturer's recommendations for the climate conditions, plantings and specific application. The plants can grow through the netting, but will hold the soil together. Figure 2 shows a generic cut-away of a common type of vegetative roof assembly that utilizes a lower granular drainage layer in combination with an upper growth medium or substrate. However, there is some evidence that, over time, these chemicals will breakdown, which reduces effectiveness, and leach off the roofs into the receiving runoff. This ZinCo green roofing system is particularly suitable for regions with extended dry periods. A conventional configuration may be somewhat more desirable in warmer climates, where the addition of a vapor retarder below the insulation would not be required.

In such cases, a drilled-in moisture probe will give the relative humidity in the concrete, but it is not known at this time what relative humidity is acceptable. Plugged installations typically include ornamental varieties and mixtures of perennials. Reliable techniques for predicting the rate and quantity of runoff from vegetative roof covers have been used successfully to design integrated storm water management measures in Germany, where large zero-discharge developments that rely heavily on vegetative roofs are already operating. Provide a root barrier, as discussed elsewhere, to protect the membrane.

After establishment of the vegetation, the maintenance is limited to one or two inspections a year. At present, the most comprehensive guidelines for vegetative roof construction, especially for growth media, are those developed by Forschungsgesellschaft Landschaftentwicklung Landschaftsbau. It is prudent to include netting, or a wind blanket, at least until the plants have established themselves. This is not desirable on an extensive vegetative roof, which is not designed to support these habitats. The question is, where does the water come from? Review project requirements for solar reflectance from adjacent buildings, mechanical equipment, photovoltaic panels, etc., that may reflect sunlight onto the vegetative roof. Non-commercial organizations that can provide current lists of vegetated roof service providers and are a useful source of up-to-date information, include: In addition, some regional groups and agencies have distinguished themselves in the promotion of vegetated roofs.

In cold climates and with high humidity occupancies the need for a vapor retarder below the insulation would thereby create two vapor retarders (the waterproofing and the vapor retarder below the insulation). With our website we try to shine light into this information jungle, because we were there from the beginning. It is recommended to avoid two vapor retarders because any water that might get between them would be trapped and not be able to dry outward or inward.

In accordance with NRCA, verify that deflection allowable under the structural design does not result in ponding. ICC also provides standards for parapet heights and requirements for railings. PECO Main office Building, Philadelphia. (For Intensive Vegetative Roofs, wildlife may be desirable. For information and standards pertaining to waterproofing materials, consult the National Roofing Contractors Association (NRCA) or ASTM International (ASTM). The green roofing system Ornamental Sedum leads to an extensive green roof with sophisticated design and individual character. A second choice would be two layers of modified bituminous rubberized asphalt cold-applied self adhering (use low VOC cold adhesive or there could be adverse effect on plants) membrane, set in liquid rubberized asphalt with aromatic isocyanurate polyol liquid waterproofing membrane. When necessary, multi-level drains to capture water from both the surface of the vegetative roof or ballast or paving and from the surface of the waterproofing membrane. Many premium roofing and waterproofing materials have been used in combination with vegetative roof installations. Other materials are likely to enter the industry as their suitability is proven in certification testing and prototype installations. Some retrofit applications, however, can result in non-trivial savings of both air-conditioning and heating. Verify the integrity of the waterproofing membrane prior to installing the overburden. al., 2008, Urban Ecosystems Vol.

Because of the transient water retention capacity of vegetative roof systems, the live loads may increase as well. Hence, they do not allow an extensive vegetative roof in this configuration, because an extensive vegetative roof is less than 6 inches thick, by definition. The total thickness of the profile should not exceed the natural root depth of the plants selected for the plant community. There is usually a vegetation-free zone (often stone ballast or pavers) at the perimeter of the roof, to prevent scouring, or soil loss and damage. ANSI/SPRI RP-14 (Wind Design Standard for Vegetative Roofing Systems) can be consulted for guidance with respect to the design of these zones. Available from. Spray irrigation should be avoided, except as a temporary means of irrigation during establishment or during emergency drought conditions. A properly adjusted irrigation system (by experienced installers) will almost always be more efficient than hand watering technique, if hand water is ever done. Given the paucity of reliable data, some designers may wish to also make this assumption based on criticality of performance, expected maintenance and other criteria. The easiest leaks to find are when a membrane is fully bonded to a concrete substrate, as it is nearly impossible for the leak to travel horizontally under the membrane. Limit public access volume and accessible areas.

Extensive roofs are an ecological alternative to conventional surface protection or ballast layers such as gravel and pavers. When joining systems of differing manufacturers, issues arise related to compatibility of products, warranty extents, long-term durability, and detailing concerns that could be avoided with a single manufacturer. Others will deliver modules with the plants fully 'grown out.' Most plugs can be safely installed after the ground is not frozen in the spring up to about one month before the anticipated first hard freeze in the fall. 1090 Vermont Avenue, NW, Suite 700 | Washington, DC 20005-4950 | (202) 289-7800 Insulation should be multi-layered extruded polystyrene (XPS) foam for PMR systems. Note 2: FM Global allows a vegetated roof over a steel deck with an appropriate FM fire test and suggests (par. There are studies that support the energy conservation aspects of vegetative roofs. These can often be purchased on short notice. If designed specifically to increase the biodiversity and attract a particular fauna and flora, they are called Biodiverse Green Roofs. If there is the desire to retain or keep a certain vegetation palette, a specific vegetation pattern or a regular full-scale flowering of its vegetation, additional maintenance efforts are necessary with an appropriate supply of nutrients. Although its principles apply to vegetative roofs in the United States, its specific recommendations apply to a central European climate. Engineered growing medium based on minerals and organic material. Suppliers of pre-vegetative mats keep standard plant selections in inventory. In other words, "green" has too broad of a connotation to be clear for use in this guide, and we recommend that the industry adopt the nomenclature "vegetative," rather than the overly broad "green. The largest share of the energy savings in the summer or warm months is from transpiration or the evaporation of water from plant leaves. A third choice would be cold liquid-applied polyurethanes. Because of the shallow profile, extensive Green Roofs also add less weight to a structure than deeper system.

In addition, the average inorganic vegetative roof medium will not support most large root systems or their nutritional requirements, further limiting plant choices to those with shallow root systems and an ability to store water.". Obtaining all components from one manufacturer ensures that all components will be covered under one warranty and that there will not be disputes over liability in case of an issue. They also preserve flexibility to re-arrange landscape designs in the future. For other climatic regions and smaller storms, vegetative roofs typically have greater capacity for runoff control. It also supplies live load requirements for maintenance-related foot traffic and for regulated pedestrian access. Acting as natural bio-filtration devices, vegetative roofs reduce this water contamination. The capacity of vegetative roofs to moderate this runoff through both retention (water holding) and detention (flow-slowing) properties has been well-documented in Europe and increasingly in the United States. In the Potsdamer Platz district of Berlin, extensive vegetative roofs have been employed on a large scale in an effort to reduce pollution of the River Spree. Typically, root barriers are in the form of HDPE (high density polyethylene) or reinforced PVC. In certain conditions such as when vapor drive is to the interior or when a concrete deck has been given a smooth finish, the results of the ASTM D4263 test procedure may not result in condensation being visible on the underside of the plastic sheet even though the concrete slab may be relatively wet. The use of electric leak detection (see below) is recommended for all systems. Trade organizations such as National Roofing Contractors Association (NRCA) are developing guidelines for waterproofing with vegetative roof installations in mind. Their conclusion is that cool roofs are better for cooling, not surprisingly, but, even in warmer climates, this benefit is overshadowed by the better performance of vegetative roofs in the heating season. Other jurisdictions offer substantial tax benefits and subsidies to promulgate vegetative roofs (Portland, Oregon, and New York for instance). Plant nourishment and support: The engineered medium must be carefully designed to provide for excellent plant growth, no wind scouring, and proper water holding capacity. al., 2004; DeNardo et. Typically, the system depth for an extensive Green Roofs rages from 4 to 6 inches (10 cm to 15 cm). This PC becomes integral with the membrane forming a very robust monolithic system. A dead roof does nothing. Many jurisdictions (i.e. On the other hand, a steep slope will provide better drainage, but can lead to slippage of materials. They are usually multifunctional and accessible. In most cases, restricting public access to extensive vegetative roofs can help to keep the building costs down, and reduce safety risk mitigation measures. Also consider compliance with the standards listed at the end of this page. For existing roof substrates, verify roof detailing exists to accommodate this test method. Combined warranty/maintenance period, and follow on warranty. At present only vegetative roofs that receive favored treatment and generous financial incentives will be able to show a positive return on investment. for 90% of the climate zones in the United States. In mild weather and with the assistance of temporary irrigation, Sedum cuttings can be relied on to generate a uniform ground cover. Accomodates a variety of vegetation based on climate, landscape design, load bearing requirements and desired benefits to building owners and communities. The growing media should be a well-drained engineered mineral soil and must be carefully designed for grain-size distribution, void ratio, moisture retention, etc. The addition of materials over the roofing/waterproofing membrane system associated with vegetative roof systems usually increases the dead load in varying amounts, based on the number, composition, and thickness of the layers of the system. 43, No. Consult with local experts on native pests and mitigation techniques, prior to pest control measures. In the winter months, there is an energy conserving benefit only if the soil remains dry.

These systems are fully bonded to the deck. Encourages wildlife to remain within build-up areas. The use of the trays greatly increases the plastic surfaces areas that retain heat. Construction oversight must find constructed leaks.

They are engineered, fabricated systems and thus present unknowns for most landscape designers, architects and installers.". In some instances it will make sense to establish a stable ground cover before introducing other plants. Our highly sophisticated green roofing system with Georaster elements even enables the installation of steep pitched roofs up to 35. Although modern vegetative roof systems have not yet been in place longer than 40 years, many researchers expect that these installations will last 50 years and longer before they require significant repair or replacement. The most common 4 extensive vegetative roof cover in temperate climates is a single un-irrigated 3 to 4inch layer of lightweight growth media vegetative with succulent plants and herbs.

If it is rainfall and not from a city's potable water, then there is a benefit. National Institute of Building Sciences Note 1: FM Global requires 8 inches of growth media with a PMR configuration (see section 2.2.3.2.2 of FM 1-35). Many vegetative installers will only warranty roof with this type of maintenance policy. If there are laps they should be thermally fused. Modules may be established at the nursery using the direct seeding or plug installation method. Vegetative roof assembly design must consider important additional factors such as the loads of saturated growing media and mature plants on building structure, the effect of wind and erosion on lightweight growing media elevated above normal grade, the temperature of the growing media around plant root systems, the depths of the growing media appropriate for plant root systems, and the risk of brush fire posed by seasonal or drought-condition dieback of some plant varieties if they are unattended.

These include: As a result vegetative roofs may be appropriate as an addition to many types of buildings, including commercial, industrial, institutional, and residential settings. If the project is insured under FM Global, then also comply with FM Data Sheet 1-28. Green Roof design by Roofmeadow. Vegetative roofs have important acoustical benefits, especially for higher frequency sounds. Stone ballast or pavers are also used around roof access and rooftop equipment. More plugs, up to about 4 plugs/square foot, will increase the rate of development of full plant coverage. Use of these systems does not relieve the designer from responsibility for considering the integrity of the underlying waterproofing system, nor does it make location of damaged waterproofing easier, it does provide cleaner and simplified access and vegetative roof replacement in the case of potential leak repairs. Different ground-covering plants that may appropriate in other climates include species of: Potentilla, Carex, Phlox, Delosperma, Crassula, Portulaca, and Aloe. There are four methods for establishing plants: direct seeding, plug planting, pre-grown mats, and modular systems.

These roof designs cannot prohibit or highly discourage the entrapment of water within the roof assembly and the membrane and insulation design is not conducive to in-place reuse or recycle in future roof iterations. In the U.S., studies have been performed to monitor the performance of vegetative roofs with regard to storm water runoff. In some cases, the manufacturer of the MB Protection Course will infuse this layer with a root-inhibiting chemical, such as copper hydroxide. To account for the R-value reduction due to the minor water absorption that occurs in PMR roofs, it is recommended that the designer reduce the board's initial R-value by 10%. US materials should not be justified based on European precedents. All seams in insulation layers should be staggered from the layers above and below by a minimum of 6 inches. All vegetative roof planting plans should include drought-tolerant ever ground-covering plants. Take time to understand the installers' warranty. Many vegetative roof warranties do not cover plant survival while some include it, provided the owner also purchases a maintenance package. Thus extensive Green Roof require low maintenance and have no permanent installed irrigation system, because it would defeat the purpose. Suitable plants include various Sedum species, herbs and some grasses. An ideal slope would be somewhere around one inch per foot. Laps may be more difficult to test than with LV testing. A professional specializing in sloped roof designs should be consulted for vegetative roofs on pitches steeper than 2:12. On the other hand, the additional cost, possible water usage to irrigate the plants, and required ongoing maintenance may make them less appropriate. NOTE: Photographs, figures, and drawings were provided by the original author unless otherwise noted. Similarly, multi-unit residences and hotels will find that vegetative roof-top views substantially enhance property values. However, sufficient time for propagation must be provided when custom plant selections are desired. Flashing details. Vegetative roofs can be designed in conjunction with solar panels, and also work very well in combination with other 'low-impact' development measures, such as infiltration beds, rain gardens, bio-retention systems, cisterns and rain barrels. Vegetative roof should thereafter be maintained by trained personnel at least twice a year. Besides the Architect and the structural engineer, participation by a landscape architect and a soils consultant may be required. They can be designed to achieve specified levels of storm water runoff control, including reductions in both total annual runoff volume and peak runoff rates for storms. The wind and fire resistance standards are still under development by the vegetative roof industry and codes/standards organizations. Protects the roof membrane from UV exposure, heat, cold and hail and mechanical damage. Green Roof advisory services and Green Infrastructure consulting. Aged compost should have been covered to protect it from weed seeds. Forty years of German experience and research indicates that extensive vegetative roofs will succeed in most climates, if properly designed. In addition, the design should use a safety factor of 1.7 for wind uplift calculations based on Data Sheet 1-28. Details for penetrations. For more information on waterproofing systems, refer to the Below Grade Systems chapter of the Building Envelope Design Guide. "Structural Considerations for Green Roof Retrofits," technical memorandum prepared by Magnusson Klemencic Associates, Inc. for City of Seattle Public Utilities department, 2007. A capillary break layer is necessary on many if not most membranes to prevent water from sitting on the membrane and causing deterioration. Pitched roof systems sometimes merge into vertical facade vegetative techniques. For both the PMR configuration and the conventional roof configuration, providing at least a minimum code compliant slope to drain, typically 1/4 inch per foot (2%), is always recommended. Thank you for visiting our website from all over the world! Waterproofing materials cannot withstand decades of root and biological attack unaided. For best results, mats should be well integrated with the underlying soil (avoiding bridging of the mats and air pockets) and irrigated regularly during the first growing season. Vegetative roofs share many engineering features with conventional storm water management basins, and compared to many at-grade storm water management practices, vegetative roof covers are unobtrusive and reliable. Climate, especially temperature and rainfall patterns. may also be employed. When designing and installing a green roof, it is important to provide a growing environment as close as possible to the plant's natural environment. It is recommended that a root barrier protect all membranes. With appropriate plant selection, sufficient drainage, and adequate structural support for the additional dead weight, vegetative roofs can survive winter ice build-up and potential summer droughts. FM Global is approving vegetative roofs for fire resistance (mostly sedums), but not for wind uplift as of this writing. In the United States, vegetative roof designs are generally regulated using existing standards for ballasted roofs. Protection of underlying waterproofing systems: Vegetative roof assemblies must protect the underlying waterproofing system from human activities (including the impact of maintenance) and biological attack, and solar degradation. In Arizona, where there is the most benefit of cooling, it is like stealing from one bucket to pay for another. Figure 5. Vegetative roofs, also known as green roofs, are thin layers of living vegetation installed on top of conventional flat or sloping roofs. For instance, drainage layers may consist of plastic sheets, fabric or synthetic mats, or granular mineral layers. FM Global calls for a minimum of eight inches of vegetative roof media if it is to be used as ballast (FM Data Sheet 1-35, par.

Figure 2. This is often prescribed in the development plan.

These include Allium, Chrysanthemum, Talinum, Dianthus, Achillea, and Phlox, as well as many grass varieties. Size, slope, height, and directional orientation of the roof. Verify that local code, membrane manufacturer or owner's standards do not require steeper slope. Their use is limited to very controlled applications, due to the increased need for maintenance. Typical pre-vegetative mats are 3/4 to 11/2 inches in thickness and range in size from 2 square feet to 25 square feet in area. Insulation should be located above the membrane, at least in cold climates or with high-humidity occupancies. Even though this climatic region is characterized by a long rainy season where soils and media are frequently saturated, storm water control capacity was demonstrated for the large storms that can cause urban flooding and sewer overflows. With respect to the vegetative overburden, this guide addresses only the more shallow extensive vegetative roofs. Electric leak detection provides the precise location of leaks, but is generally not acceptable for use with black EPDM membranes due to the high conductivity of carbon black in the membrane. A minimum initial planting density, in most cases, will be two plugs per square foot. The systems used to stabilize pitched roof installations depend on the underlying structural capacity and design, and the steepness of the roof. After all, plants care about the porosity of materials, Air-to-Water Ratio, and nutrient exchange capacity to name a few. (Example: Localize burning of plants has been documented as late as September in New England.).