Long a player on roof gardens and green buildings, Tournesol Siteworks is now creating component solutions for the modular green roof marketplace.  As the country realizes the benefits that a green roof provides (see the “How it works” tab), more developers are committing to covering at least a portion of their roof with plants.

With the market still in its infancy, there are many different answers to the “right way” to set up a green roof.  The most common solutions in use now are built-in-place and modular. Tournesol is working from our years of experience manufacturing liners for plants and planters, and creating components for the modular green roof segment.  The market is currently roughly split between the two concepts. 

A modular green roof is made up of a series of trays, which hold engineered soil and plants. This allows the use of a green roof directly on existing roofing membrane, without retrofit and the associated risks and costs. It still provides the important elements associated with green roofs, including stormwater retention, insulation, and membrane protection. Tournesol Siteworks green roof trays are made of recycled HDPE material, and come in a variety of sizes for both extensive (4”) or intensive (8”) soil depths.  Custom depths and sizes are available as required.

 

A quick summary of advantages of modular green roof systems vs. built-in-place:

• Easy roof repair & maintenance – just shift the trays to the side and fix whatever is wrong with the roof.  No digging, no tearing out existing healthy plants, and less “down time” due to roof membrane problems.
• Quick & easy installation – most of the installation work can be done on the ground.  It’s safer, faster, and costs less than working on the roof.  Arranging trays is all that’s required on the roof.
• Easy green roof maintenance – if there is a problem with a section of the plantings, it can quickly be “switched out” with another tray, rather than worked on in the field.
• May be retrofitted to existing roof (depending upon structural capability), no special roof membrane required.
• Pre-engineered components mean less custom design is required.
• Lightweight – like built-in-place systems, the modular tray system retains a specific amount of stormwater prior to allowing the rest to drain.  Unlike the built-in-place systems, there aren’t heavy layers of additional water-retention fabrics, drainage layers, etc. required.
• May be pre-planted and pre-grown – a mature roof planted without waiting.

 

Characteristics of the Tournesol modular trays:

• Available in a range of sizes for both extensive and intensive applications.
• Manufactured in recycled high density polyethylene (HDPE), with 60% post-industrial recycled material.
• Drainage channels in the trays allow for normal water flow across the roof.
• Raised drain holes (on channels) allow for storm water retention and water reintroduction to water cycle.
• Trays manufactured in black material with UV stabilizers.
• A full range of edge treatments and connection options are available.
• Typical saturated weight of 4” (extensive) system – 15 lbs. per square foot.
• Sold through local distributors, keeping the overall cost to the contractor low.

 

Tournesol Siteworks can also assist with specification of engineered soil, recommended plants and project plans if requested.

Why install a green roof? 

Benefits to the Natural Environment:

• Reduction of the urban heat-island effect.  Most cities consist, to a large extent, of paved areas and building rooftops.  These absorb the heat during the day and retain it, which is then radiated back into the atmosphere.  This has been shown to increase temperatures around major cities by 3-8ºF. Green roofs are (ideally) covered with plants, which shade the building rooftop, and prevent it from absorbing the heat or reflecting it back into the atmosphere.
• Stormwater Retention.  Rainwater falling on a normal rooftop is immediately shunted into the drainage system, with little or no opportunity to be brought back into the water cycle.  Plants in green roof systems can utilize any rainwater absorbed into the planting medium, and transpire that directly back into the atmosphere. See also benefits to the built environment.
• Biodiversity.  By propagating green spaces, we are giving critical species of insects and birds locations to live.  This was one of the primary drivers of the German marketplace. This is the most “green” of the arguments.  An effort is underway in the San Francisco Bay area to create a series of green roofs in a chain throughout the area, to allow for birds and insects to be able to repopulate areas that they had been unable to reach due to massive development.

 

Benefits to the Built Enviroment:

• Energy efficiency.  A green roof on a building absorbs much of the UV radiation, preventing it from striking the roof and heating the building. The green roof also provides a layer of insulation, isolating the inside temperature from the outdoor temp. Most any commercial building will keep a consistent temperature no matter the external factors, so there are two major benefits here – the heating and cooling units won’t need to work as hard, which will save energy, and because the requirements on the system aren’t as great, a smaller heating/cooling unit can be installed, saving on building construction costs.
• Stormwater Retention.  All water that currently falls on a regular roof quickly runs into the drainage system. This is typically passed through to the municipal sewer/storm drain system.  In many municipalities, development has reached a point that major storm surges will overwhelm sewers and water treatment facilities. This may only be a problem of short duration, but the only solution is to either expand the sewer system (digging up and expanding them!), or changing the flow profile of the run-off.  Green roofs accomplish this with a water retention layer designed into the system.  In the case of Tournesol’s modular tray system, the drainage holes are raised ½” off the roofing membrane. The water accumulates in the water storage cells, where it can be used later by the plants. Exact studies demonstrating the quantifiable benefits of these systems are being carried out, and are expected to drive code requirements in the long run.
• Protection of roofing surfaces. It has been shown that a protected roofing membrane (from UV, heat, temperature fluctuations, etc.) can last two to four times longer than unprotected membrane.  The savings in re-roofing the building can help offset the cost of the green roof.

Types of Green Roof Systems

Built-in-place vs. Modular

Most flat roofed buildings in this country are covered with either single-ply membrane or fluid applied rubberized asphalt waterproofing.  Green roofs are typically done on single-ply membrane roofs, the more expensive and reliable roofing solution. Built-in-place greenroofs are what they sound like - made up of single-ply roofing membrane, which is then layered with a plastic drainage material, another non-woven layer and water retention material, then 2+ inches of an engineered soil medium poured on top.  While the built-in-place green roof has a high level of flexibility and aesthetic value, it also is expensive to install and dependent upon the long-term success of the roof membrane.  Modular systems are essentially a series of trays, each of which holds a thin non-woven drainage fabric, engineered soil, and plants.  These systems offer significant installation and maintenance advantages. They tend to be considered more functional and less aesthetic (although once the plants grow in, it can be difficult to tell modular from build-in-place apart).

Extensive vs. Intensive

Greenroof projects that require no active, ongoing maintenance are called Extensive.  These are typically 4” deep (although they can be planted in as little as 2” of engineered soil), with simple or no irrigation, drought-tolerant plants (often sedum) which require little or no care.  This is the least expensive to install here.  The “maintenance-free” aspect of the roof is attractive, although they do need seasonal maintenance..  The plants on these types of installations will not withstand being walked on.  Our 4” modular trays are made for extensive applications.

Everything else is referred to as Intensive. Intensive can be from 6” up to several feet of soil, is often irrigated, and has a richer variety of plants.  They are also much more expensive than extensive roofs, and are typically custom designed by a specialist. Most of the really high profile projects are done as intensive, although the majority of greenroofs put in are extensive. Our 8” modular trays and modular trays with AutoFill are made for intensive applications. 

Model	Description
GRT-242404	Extensive Green Roof Tray, 24”l x 24”w x 4”d,
GRT-482404	Extensive Green Roof Tray, 48”l x 24”w x 4”d
GRT-242408	Intensive Green Roof Tray, 24”l x 24”w x 8”d
GRT-482408	Intensive Green Roof Tray, 48”l x 24”w x 8”d

Design Services – Tournesol Siteworks can assist you with the details of your modular green roof, including overall design, soil specification, plant selection, and irrigation, should you need it.

Engineered Soil – Working together with experts in the industry, Tournesol has developed an engineered soil mix perfect for our system.

Edge Treatments – If people will be walking around the modular green roof, you may want to finish the edges.  We have solutions in wood, metal, and fiberglass.  Just ask your salesperson for details.

Alternate Fill Materials – the green roof tray can be used for other fill materials, either for effect (like crushed glass or pebbles), or to get the stormwater retention materials and membrane protection with no maintenance.  Ask your salesperson for information on these uses.