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General industry misconceptions about vegetative green roofs and GreenGrid

There are common misconceptions across the construction industry regarding the cost, weight, installation, maintenance requirements, and performance of vegetative green roofs. Click on a subject below to find the answers to frequently asked questions that we field nearly every day.

FEATURES

- What makes GreenGrid different?

  • GreenGrid remains modular for the life of the product. With no edging requirements, it is simple to install and provides an instant vegetative green roof on day one.

- What makes GreenGrid better than other tray-type options and built-in-place systems?

  • Delivery with 70 to 90% plant coverage and installation of 3,000 to 6,000 square feet in one day makes GreenGrid the industry leader in simple installation. GreenGrid maintains its modularity for the life of the product, guaranteeing hassle-free access to the waterproofing membrane if a leak develops.

- Do you offer different soil depths?

- Are modules pre-vegetated to full coverage?

  • With sufficient lead time, modules are grown out to 70 to 100% plant coverage.

- How can I achieve my aesthetic goals with a vegetative green roof?

  • Using a mix of extensive and intensive modules with various plant mixes can create a unique, expensive-looking vegetative green roof that can be turned into an accessible space using hardscape features such as pavers, benches, and tree boxes. Specific color palettes and textures can be achieved using grasses, perennials, and sedums. If you need help with your design, WESTON offers complete landscape design services.

- How do I incorporate irrigation?

  • GreenGrid modules have an integrated irrigation line channel built into the module, so running permanent irrigation tubing beneath the modules with pop-up spray heads is intuitively designed. Temporary irrigation can also be incorporated by laying tubing on top of the modules and within the vegetation.

- How does a module drain excess water?

  • The bottom of a GreenGrid module uses a waffle-pattern design with drainage holes and water retention cups to contain some excess water for the plants to draw from in time of drought and for stormwater storage. When the retention cups are at capacity, water drains through the raised drainage holes through the drainage channels.

- What is the best application for GreenGrid and/or modular?

  • GreenGrid is most effective on flat roof surfaces (maximum slope of 1:12) using the largest continuous roof area. It can also provide green space for roof decks and accessible terraces. Slightly higher slopes up to 2:12 are feasible but may require additional engineering controls.

DESIGN

- How do I design with GreenGrid

  • Visit the Design section of our website for details on how to design your next project with GreenGrid.

- Can I choose which plants are used?

  • WESTON welcomes our clients to create their own plant mixes, which we will review for rooftop suitability based on hardiness zone and past performance. If the plants submitted are not deemed suitable, we will suggest substitutes that maintain the desired aesthetic while ensuring plant survival.

- How do I incorporate hardscape (i.e., benches, walkways, etc.)

  • GreenGrid modules can be placed on top of or next to pavers to create walkways, patterns, or designs. Benches can be integrated the same way. To make pavers level with modules or roof slopes, use shims to achieve the desired height.

- What do I do around penetrations and perimeters?

  • Because GreenGrid is fully modular, there is no need to install edging or drain boxes around penetrations and perimeters. Modules can be placed as close to the penetrations as desired and empty space can be left open for easy access or be filled with river rock for aesthetic effect. Around the perimeter of the roof, SPRI and FM Global recommend leaving a buffer of 8.5’ to ensure that wind uplift does not occur.

- Can GreenGrid accommodate curves?

  • Modules can be cut to accommodate curves, using flexible edging to contain growth media and vegetation. Empty modules will be shipped with the order to be cut on-site and filled with media and plants from pre-vegetated modules. The rest of the field will remain in 2-ft x 2-ft modules.

- What kind of waterproofing system is GreenGrid compatible with?

  • GreenGrid is compatible with nearly every kind and brand of waterproofing. For most manufacturers, all that is required to maintain the waterproofing warranty is a 12-oz geotextile slipsheet to be placed between the roof surface and the modules. Check with the waterproofing manufacturer to obtain its specific warranty information.

- Does GreenGrid work with Electric Field Vector Mapping (EFVM®) Leak Detection Systems?

  • Yes. Modules do not inhibit use of EFVM electrodes and can make it easier to pinpoint leaks because modules can be removed easily once the location of a leak has been narrow down to a specific area. Then the leak can be pinpointed. This is not as easy to do with layered and hybrid systems because it requires digging up the vegetation and growing medium to get to the waterproofing layer to pinpoint leaks.

- Does it attract wildlife? (Birds, bees, butterflies)

  • In general, the plants used on vegetative green roofs attract bees and butterflies for pollination, increasing overall biodiversity for the area and providing natural corridors for various species.

- Should I set back from vents/HVAC equipment/perimeter? Are there places to avoid?

  • Maintaining a 2-ft walkway around vents and HVAC equipment will allow for easy access to the equipment for maintenance and will ensure that the plants are not damaged by unexpected shade, wind, microclimates, or foot traffic.

- Are there any safety requirements that should be incorporated?

  • Incorporating anchor points into the roof design for maintenance activities if the parapet walls are less than 48 inches tall is recommended. Comply with all OSHA regulations as well as any local jurisdictional safety requirements.

- Do I need to use edging?

  • Edging is an aesthetic option that is not required for a fully functional system but may be used if modules are cut to accommodate for curves or other non-square areas.

- What happens in the winter?

  • The plants will go dormant during the winter and shrink slightly unless evergreen varieties are chosen. All varieties will return in the spring.

- Does it work in the shade?

  • Specific plant varieties can be chosen to accommodate for partially shaded roof areas. There is more room for native varieties to be used in shade, which also may require specialized growing media. Fully shaded areas are not recommended.

- Are there considerations to be made for accessible spaces?

  • Be sure to design the space to be compliant with 2010 ADA Standards for Accessible Design, incorporate a 42-inch parapet or railing, and use plant mixes that make use of a variety of textures, colors, and heights for visual interest.

- How do I create a rooftop garden on a budget?

  • Mixing 4-inch extensive and 8-inch intensive modules along with some hardscape creates an interesting change in height and textural aesthetic.

- What can I do to make my green roof more interesting than just using sedum?

  • Accent plants, benches, pavers, stone ballast, 8-inch modules, and edge treatments can make a standard extensive green roof have a more attractive look.

- How do I accommodate for slope?

  • If the slope is slight, the modules can either follow the slope directly by placing them atop a slipsheet, or they can be placed onto pieces of tapered insulation to make the roof appear flat. Slightly higher slopes (maximum of 2:12) can incorporate engineering controls at the bottom edge of the slope as a “stop” for the modules or within the vegetative green roof field.

- Aesthetics are a main consideration for my vegetative green roof—what do I do about the grid lines created by the modules?

  • By choosing plants that have a spreading growth habit as ground cover in addition to clumping plants, both having evergreen foliage, module lines will be nearly invisible. The all new G4 module design incoprorates zero-edge perimeter design to achieve this effect, yet remain truly modular for easy access to the underlying waterproofing throughout the life of your roof.

INSTALLATION

- What is the rate of installation?

  • Between 3,000 and 6,000 sf of GreenGrid modules per day can be installed using a crew of 6 to 8 people.

- What goes underneath?

  • A 12-oz geotextile slipsheet is all that is required by most waterproofing companies. A loose-laid layer of EPDM may also be used as a slip sheet. Check with your waterproofing company to ensure warranty coverage.

- Do the modules interlock?

  • The modules sit directly next to each other and using universal alignment notches on each side to ensure a tight fit. Modules can be zip tied together if wind is an issue.

- What equipment do I need to install the system?

  • Use a crane, lull, or boom truck to get skids or racks up to the roof. From there, a pneumatic tire roofing cart is helpful to move the modules to their desired location. Elevator installations are not uncommon, but may take longer than hoisting material directly to the roof.

- How much lead time for order placement?

  • WESTON strives to deliver modules at 75 to 90% coverage, so lead time is critical to installing a mature vegetative green roof. Lead times range depending on location, project specification, and time of year. Allow 4 to 6 months, but faster times are often available. Contact your local Weston GreenGrid representative to discuss availability for your project.

- How do the modules ship?

  • 2-ft x 2-ft x 4-inch standard extensive modules are stacked on pallets with spacers between units and shrink wrapped for delivery. Nursery racks may be used for 6-inch and 8-inch modules, or special planting selections that may require them.

- Do I need to be/use a certified installer?

  • There is no certification required to install the GreenGrid system. WESTON provides an installation guide, which gives recommendations and standard procedures for installers to follow to ensure proper installation. Contact your local representative for details.

- Can I install it myself?

  • WESTON does not provide installation services, so using a roofing contractor or landscaping contractor or self-installing are the most common options for installing a green roof.

- Do you have an installation manual?

 

MAINTENANCE

- What level of maintenance is required?

  • We recommend six events per season: two major and four minor. A major event is widespread weeding, fertilizer application, replanting as necessary, and plant health evaluation. Minor events include spot weeding, watering as needed, and plant health evaluation. After about 2 years, maintenance requirements decrease significantly, but should not be stopped completely.

- Do I have to mow my green roof?

  • No. Sedum spreads outward more than upward, but it can be mowed or trimmed to create cuttings, which propagates more plants. Perennials and grasses need to be cut back either in the spring or fall maintenance event to ensure proper growth.

- What kind of fertilizer should I use?

  • You can choose a conventional slow-release fertilizer (example: Harrell’s or Miracle-Gro®) or an organic slow-release fertilizer (example: Espoma® Plant-tone®).

- Do I have to use fertilizer?

  • WESTON recommends fertilizing once per year because there is very little organic material in the growing media; fertilizing helps to keep the plants healthy.

- Do I have to irrigate?

  • If aesthetics are your main driver for purchasing a green roof, then irrigation may be a good option for you to consider in order to maintain lush plants throughout the hot dry summer months. Permanent irrigation is not required for the extensive system in most cases, however, you location and plant selection may dictate otherwise. Irrigation is highly recommended for the intensive system. Contact your local Weston GreenGrid representative to discuss further.

- Does WESTON offer maintenance services?

  • WESTON can provide cost estimates to self-perform maintenance services, or we can recommend contractors who have experience and success in maintaining our system.

- Do you have suggested maintenance activities?

- What are signs that my vegetative green roof is not being adequately maintained?

  • The presence of weeds, discolored or scorched plants, small plants, and plant loss are all signs that your vegetative green roof is not being properly maintained. Plant health cannot be evaluated until after the last frost of the spring because plants take varying amounts of time to come back from winter dormancy. All plants should look healthy and viable by May in most areas.

- Do I need to pull weeds?

  • Yes, absolutely. Weeds can become a problem when they are not regularly pulled because they can choke out the plants and take over the green roof.

- What happens if I don’t maintain?

  • Plant loss, weeds overtaking, stunted plants, discolored plants. Vegetative green roofs are living systems and require varying levels of maintenance. While we may design a LOW maintenance vegetative green roof for you, there is no such thing as a NO maintenance vegetative green roof.

 

WIND/FIRE

- Are there guidelines for windy roofs?

  • Yes, and WESTON recommends designing to SPRI and FM Global standards.

- Will the modules blow away?

  • If high wind speeds are a concern, consider zip-tying the modules together, using edging, or not incorporating a green roof at all.

- Is a green roof a fire hazard?

  • The GreenGrid system has been fire tested and is not considered a fire hazard.
 

 

PERFORMANCE

- Why is GreenGrid better?

  • The GreenGrid system is the product of over a decade of research and testing. The result is a complete vegetative green roof solution that is flexible, easy to install, and requires minimal maintenance. Because it is modular in nature, a GreenGrid rooftop design can be easily adjusted and rearranged after installation to meet a change in stylistic preferences or planting schemes. Most important, roof maintenance and repair are easily carried out with this system. Unlike hybrid modular systems, GreenGrid modules can simply be moved to address a maintenance issue and then put back in place very easily.

- What can I expect for stormwater management?

  • o Greater that 70% of a 1 inch, 1 hour rainstorm absorbed for typical extensive GreenGrid systems and in excess of 90% for our 8-inch intensive system.
  • 40 to 60% reduction of stormwater annually

- What can I expect for energy performance?

  • The GreenGrid system has been evaluated for energy performance, and third-party researchers have determined that the effective R-value for the extensive system is a 100 in the summer and a 4 in the winter.
  • Due to their superior insulating properties, vegetative green roofs have consistently been proven to reduce heating and cooling costs by up to 25% and 50%, respectively, for the floor directly below the roof. Rooftop surface temperatures impact not only the temperatures within the building, but also the amount of energy necessary to heat and cool the building to the desired temperatures.

- How does this help with LEED?

  • o If the system is installed on 50% of the roof area or more, GreenGrid virtually assures 2 points under SS Credit 6.2 – Storm Water Design: Quality Control and SS Credit 7.2 – Heat Island Effect: Roof., and GreenGrid can contribute to 7 or more points in conjunction with other sustainable products and practices being used.

- Are all vegetative green roofs the same?

  • There are different types, styles, and depths to consider for a green roof. Modular, built-in-place, or hybrid are the predominant versions of vegetative systems, and ultra-extensive, extensive, semi-intensive, and intensive are the main depth categories, ranging from 2.5 inches of soil media to 2 feet or more. Why GreenGrid?

- Why would I want to retain water in my vegetative green roof?

  • Stormwater retention is a driving factor for vegetative green roof incentives across the country, and a little extra water storage during the summer months can help plants to stay viable during harsh seasonal conditions. The occurrence of root rot is negligible in a properly designed system.

- Is a contained system healthy?

  • Sedum varieties are used to growing out of the rocky terrain of alpine environments with few extra nutrients, so growing in a modular system does not inhibit growth or take away from nutrient sharing across the system. It is a common misconception that interconnection between modules is needed or required.

- What can I expect from the plants during the year?

  • Winter: Non-evergreen plant varieties will be dormant and appear dead, but evergreen varieties will keep foliage.

  • Spring: Some plants flower in early spring, others stay dormant longer. All will be out of dormancy by May.

  • Summer: All plants should look healthy and colorful. Greens, blues, reds, yellows, and purples will cover the roof.

  • Fall: Plants will start to go dormant. Evergreen varieties will turn orange/red.

- Is it really going to make my roof last longer?

  • Because your roof membrane will not be subjected to extreme changes in temperature, expansion and contraction, and UV rays, it will last at least twice as long as an exposed membrane.

- What if I have a leak?

  • The beauty of the modular system allows for easy removal of the overburden layer without disturbing plants or layers. The modules can be moved to another area until the repair is completed, and can then be placed back into position. Compare this to the excessive work necessary to excavate and uncover the waterproofing layer in hybrid and built-in-place layered systems.

- What is the warranty?

  • Modules (plastic) are warranted for 20 years. Media is warranted for 15 years, and plants are warranted for 30 days (plants and labor) and 90 days (plants only), unless an extended warranty is purchased and documented proof of maintenance is provided to WESTON. WESTON also includes the plant warranty if we are contracted to do the maintenance.

- Does it stay in the tray?

  • The GreenGrid system is modular for the life of the product; media and plants stay in the tray indefinitely.

 

MISCELLANEOUS

- Can I walk on it?

  • Vegetative green roofs are not soccer fields, but they can be walked on for maintenance of the vegetative green roof. If the roof area has a lot of HVAC equipment, walkways should be built into the design so that these units can be serviced. Accessible spaces should also incorporate pavers to differentiate between the accessible area and the green roof.

- What kinds of plants are used?

  • For the extensive system, a variety of sedum plants are the most common and reliable, along with Allium, cactus, and other zone-specific accent plants. The intensive system can be planted with a host of perennials and grasses.

- Are they native?

  • Sedum plants are considered adaptive by the USGBC, but native plants can be incorporated if the site conditions allow.

- What kind of plastic are the modules made of?

  • 100% pre-consumer recycled high molecular weight polyethylene protected with UV inhibitor and stabilizers.

- What is the cost?

  • Depending on the size and depth of your vegetative green roof, cost commonly ranges from $11 to $18 per square foot. Larger projects can dip into the $10 range, while small projects can reach $20. WESTON offers free designing and estimating services, so please contact your local representative to get specific pricing for your project.

- What is the media made of?

  • GreenGrid growing medium is an engineered lightweight blend consisting of inorganic and organic components. Formulations are based on the German FLL “Guidelines for Planning, Execution and Upkeep of Green-Roof Sites,” but vary slightly from region to region to accommodate for varied climates and regional raw material resources.

- Where are the plants grown?

  • WESTON partners with local nurseries to provide the plants and labor to fill, plant, maintain during grow-out, and ship to the project site. We have these relationships across the US and Canada in all major vegetative green roof markets.

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