Assessment | Waterproofing | Structure | Soil & Plants | Brands We Proudly Install

A greenroof is not simply plants placed on the rooftop, but rather a highly-engineered contiguous system of plantings designed to protect the structural integrity of the building while providing significant environmental, economic, and aesthetic benefits.

At D.C. Greenworks, we believe that no one greenroof system fits all. While every greenroof has the same general components and minimum requirements, manufacturers can vary greatly, and often include patented bells and whistles you don't really need.

Our Greenroof Meadow System is non-proprietary, and is comprised of components from different companies to save on cost. This generic system can meet or exceed nearly all greenroof component specifications in the U.S.

We also install most greenroof name brands, including modular systems like GreenGrid. This means that we will work with you to customize the greenroof specifications to fit your design and site requirements, while keeping the price low.

There are three steps to putting on a greenroof: structural assessment, waterproofing, and greenroof retrofitting.

1. Structural Assessment
Greenroofs must account for the saturated weight of the greenroof and load bearing capacity of the underlying roof deck; moisture and root penetration resistance of the waterproofing membrane; resistance to wind shear; management of drainage; and the suitability of plant material.

Loading capacity for the roof must be determined by a structural engineer or architect prior to installation. The first step in any installation is to get this done for your home or property.

Greenroof systems contain several layers of protective materials to support your greenroof and convey water away from the roof deck:

2. Waterproof Membrane
The highest priority of a greenroof installation is to keep the building watertight. First, a new waterproof membrane is installed. This membrane must be made of an inert material such as 45-90ml single-ply PVC, TPO, or EPDM. Built-up hot-applied high-polymer asphalt, 2-layers of high-polymer SBS modified bitumen with a root barrier are also acceptable. Turn-metal, slate, shingles, tar, and conventional asphalt are not compatible with greenroofing.

Because a greenroof should only be installed on a new waterproofing membrane, the most cost-effective time to greenroof is during new construction or addition, or when you need a roof replacement. Are you Roof-Ready?

The membrane should be checked thoroughly for leaks prior to greenroof installation. Some greenroof installations use EFVM technology to ensure there are absolutely no leaks (even the size of a pinhole) before the greenroof is applied over the waterproofing membrane. EFVM can cost as little as $1 per square foot, and if your waterproofing should happen to leak, it is virtually 100% accurate in pinpointing breaches with minimal disruption to your greenroof. This technology can let you sleep easy and dry, even if you don't have a greenroof! D.C. Greenworks offers EFVM as an optional upgrade on compatible greenroof projects.

Lastly, an optional insulation course can be installed over (or under) the membrane to provide even greater energy savings to your building. Polystyrene insulation can also be used to create lightweight landscape contours, hills and valleys in your greenroof design. Insulation is installed either under or over the membrane in the same way as in conventional roofing. If installed above the membrane, the insulation is ballasted by the greenroof system.

The second step in any installation is to find a qualified, competitive roofer who can install the membrane appropriate for your building and your greenroof.

3. Greenroof Structure
On top of your waterproofing (and insulation, if applicable) are the greenroof structural components, which include a drainage layer, a filter fabric for fine soils, and an additional root barrier. If the greenroof is higher than five storeys or located in a windy area, a biodegradable jute erosion blanket is placed over the new plants to stabilize establishing roots. Roofs with a slope of 20 degrees or more also require additional support to prevent shearing and erosion. Finally, aluminum, steel, stone, concrete, or wood retention curbing is used to separate the greenroof system from the outer perimeter, penetrations, and drain areas of your roof. The perimeter, penetration, and drain areas are filled with gravel or pebbles, providing additional drainage, fire control, and access to the roof for maintenance.

Modular greenroofs, such as the GreenGrid or GreenTech systems, integrate the drainage and filter layers into molded plastic planter trays no larger than 4'x4', which are installed on your rooftop like greenroof "tiles." The trays eliminate the need for curbing, though on publicly-accessible greenroofs, it is necessary to finish any exposed plastic edges with wood, stone, Trex, etc. The modules come in preset rectangular sizes, so they are not meant for curving or contoured greenroof designs. However, greenroof modules can be pre-grown, providing instant impact not possible with a layered system. Because modular systems are prefabricated, "out-of-the-box" greenroofs which are quickly installed or removed, the components cost a lot more per square foot than layered greenroof systems. However, on large-scale or tricky installations, their quick and easy installation can save a lot on labor and maintenance costs.

The third and final step in your greenroof retrofit is the installation of the greenroof system components and plantings.

D.C. Greenworks installs the traditional layered Greenroof Meadow System (shown above), as well as the two leading modular systems in the U.S. today. We do not endorse a particular system because each has advantages over the others depending on the site and the client's needs. We enjoy working with you to choose the greenroof system that is most appropriate for your site, your goals, and your budget. Get an Estimate!>>

Greenroof Soils and Plants
On top of the drainage and filter layers, the growing medium or soil substrate is installed to the depth specified for your design. This growing medium is not topsoil. In fact, it barely looks like soil at all. Greenroof media is a custom-engineered growing medium made of expanded shale, mushroom compost, and mineral components. This medium is very lightweight, erosion resistant, and contains just the right nutrients for low-maintenance plantings.

The two basic types of greenroofs are extensive and intensive greenroofs. This is determined by the depth of the media on your greenroof. Extensive greenroofs are typically only 3–4 inches deep, weigh between 15–30 lbs/sf, and are usually planted densely with sedums or similar low-maintenance species to create a meadow effect. Extensive greenroofs will survive even extreme drought, though the plants may go dormant for a while. In hot, dry summers, some irrigation may be necessary if you want your greenroof to stay lush.

Semi-intensive roofs can vary from 4–8 inches of media, supporting wildflowers and drought-tolerant, herbaceous perennials. At high elevations or in hot, dry summers, semi-intensive greenroofs may require irrigation. Intensive greenroofs vary from 8 to 12 inches (or more) of media, supporting shrubs, trees, and even fountains and ponds. Intensive greenroofs can vary from 30–150 lbs/sf or more. Intensive greenroofs usually need daily, timed irrigation during the summer, especially at high elevations.

D.C. Greenworks' Greenroof Meadow System (shown above and in Completed Projects) is an extensive system. We also install both the GreenGrid and GreenTech modular systems, which are also extensive. Extensive meadow plantings are designed to suit your taste and site requirements. For publicly-accessible, semi-intensive and intensive greenroofs, D.C. Greenworks provides custom design services. We enjoy working with you to design the greenroof that is most appropriate for your site, your dreams, and your budget. Get an Estimate!>>

We are proud to install greenroof systems and components from these industry leaders: