Landscape Architecture, Ecological Restoration and Planning

The Greening Series

Rain Gardens

Green Roofs & Rooftop Gardens

Up on top for a green world

By S. Edgar David, RLA, ASLA


Trail Systems (coming soon)


Neptune Elementary School Green Roof Garden


The growth of Green Roofs and Rooftop Gardens in the United States has been impressive over the past 10 years. The realization that rooftops provide great opportunity for a number of uses has lead to the very literal 'growth' of rooftops.  Urban areas in particular are seeing significant use of this pragmatic approach to utilizing every last square foot of available space. The benefits reach far beyond merely providing an added space to recreate or garden. As the greening of cities movement continues to grow we are becoming more aware of the continual benefits that stem integrating biological systems into our lives. The Green Roof can instantly remedy a number of typical homeowner concerns. Here at SED Design we strive to create spaces that are multi-functional. Whether your roof top is a shallow extensive green roof used to manage storm water or a deeper more diverse intensive rooftop garden providing outdoor living space, there are many benefits and opportunities up on the roof.

Extensive Green Roofs

Extensive green roofs are thin, 3”-4” lightweight veneers consisting of a drainage layer to assure positive drainage, engineered growth media to support plants, not to be mistaken with topsoil, and vegetation to stabilize the media. This transformation of impermeable barren rooftops with living biological systems that absorb and filter rainwater, reduce the urban heat island effect and reduce particulate matter to improve air quality, vastly improves the environment. These environmental benefits are driving todays growth in the green roof market.  When applied on a large scale green roofs can transform the quality of our urban world.


Life Expression Healing Center

Sym van Der Ryn Architects

Intensive Green Roofs

Going beyond extensive green roof systems, Intensive green roofs which involve the same basic elements offer many expanded opportunities for growing more diverse plants that is beneficial when creating usable space for private terrace gardens, public gathering areas or production gardens that require deeper media profiles.

Taylor Residence

Kennett Square

Weight, The Rule of Thumb

An engineered green roof systems, utilizing light weight growth media weighs 7 lbs. per inch per square foot in a saturated condition.  Therefore a minimum 3” system will weigh 21 lbs. per square foot while a deeper 8” system, suitable for growing a lawn, will weigh 56 lbs. per square foot and so on. Building codes create structures that can easily support the weight of extensive green roof systems while intensive systems may require some additional structural engineering.


Flat or Sloped

For the construction of green roofs flat or slightly pitched roofs are preferred for simplicity purposes. Flat roofs also have the potential as useable outdoor space. Sloped or curved roofs are often much more dramatic and allow them to be seen from the ground require some specialized slope engineering to retain the growth media.  A slope less then 1:12 or 8.3% generally does not require any specialized slope stabilization while 1:12 begins to trigger strategies to assure that the growth media stays in place. The steeper the slope the more complex the stabilization becomes all the way up to vertical slopes or Green Walls that is a matter of another discussion.

PECO Headquarters Green Roof

Creating Rooftop Terraces and Decks

With the growth and evolution of green roofs and rooftops gardens the development of new systems are continually evolving and creating many new opportunities.  Decking systems can be easily installed on specially designed pedestal systems that are adjustable to allow for level terraces and decks on otherwise slightly sloped roofs.  Pedestal systems can support both masonry terraces and wood decks while allowing rain water to drain through and across the water proofing membrane below.


In less formal applications paver's set on the media is simpler particularly for maintenance walkways and for utility access.


Installation Example

Water Proofing Your Rooftop

Although a green roof is not in itself a water proofing system, the design of the waterproofing in conjunction with the green roof is essential.  Green roofs are known to extend the life of a waterproofing membranes for many decades generating huge cost savings over the extended life of the roof.  Depending on the type of water proofing different strategies in the design of the green roof can be implemented to make sure the green roof and the water proofing membrane are compatible.

To Irrigate or Not

Due to the droughty well drained nature of extensive green roofs they are designed with plants that are adapted to those conditions.  These plants, many of which are sedum species have special mechanisms that allow them to go dormant during extended periods without rain and then spring back to life when the rains come.  Although this is acceptable for green roofs meeting storm water management requirements roof top gardens that are more active spaces will benefit from an irrigation system to supplement the season water supply.  Irrigation will keep plants looking more vibrant and will open the door to many more plants that would not survive the droughty conditions of an unirrigated green roof.

Extensive Sedum Planting

Two basic categories of irrigation systems for green roofs include surface irrigation and base irrigation.  Surface systems are adapted from ground level irrigation systems designed to deliver water to the surface of the growth media and filter down through the media profile filling the pore space and providing moisture to the roots of the plants.  Base irrigation systems flood the bottom of the green roof system which helps to draw the roots of the plants down deeper into the growth media and drainage media in deeper systems.  Deeper root systems are more tolerant of fluctuating conditions and make the plants healthier and stronger.  For this reason base irrigation systems are preferred for green roofs over surface distribution systems.

Shading and Trellising for Human Comfort

The nature of rooftop gardens, fully exposed to the sun’s radiation, often limits the comfortable use of the space.  Trellising and shade structures integrated with rooftop gardens extend the usable periods for these otherwise incredible outdoor spaces and rooms.  Unlike the green roof system shade structures require special anchoring and stabilization consideration. These structures projecting from buildings or extending above the roof plane, are susceptible to often sheering wind forces.  Shading structures need to be carefully designed to withstand such forces.  The two basic methods include anchoring the structure to the building and/or the roof structure itself.  Anchoring to the roof structure requires penetrations of the waterproofing membrane.  An option to creating more membrane penetrations is to support the shade structure with supports that are spread across the roof and ballasted by the green roof and terracing systems.


Solar Panels and Green Roofs make a dynamic partnership

Integrating Photo-voltaics and Rainwater Cisterns

Integrating solar panels to generate electricity or cisterns for rain water  harvesting are complementary technologies with green roofs.  Solar panels perform at greater efficiency when cooled by evapotranspiration from green roof plants.  Solar panels can be used to generate electricity for garden lighting or run a pump for a solar fountain that circulates water.   Rain water harvesting captures excess rainwater for future use and to reduce detrimental storm water runoff.


Whether your green roof is for personal gratification, to meet storm water management requirements or for LEED/SITES Certification and the creation of healthy sites, SED Design brings both function and beauty to your project through creative engineering and design.


Guardrails for Safety

Personal safety is always the most important factor on a green roof and there are many codes that require design details to meet those regulations.   Guardrails are always required on any rooftop that has any used space.  Green roofs that merely serve for environmental and aesthetic functions may not require a guardrail, but they do require stantions or tie-offs so that maintenance workers can tie in while performing routine maintenance visits.


Safety First

Green Roof Care

Everything takes some degree of maintenance to sustain the maximum benefits and desired aesthetics.  Green roofs are no exception.  Depending on the role of the green roof and the level of use, maintenance programs range from a few visits a years by trained green roof horticulturists to more rigorous weekly visits for important outdoors spaces.  Of course the home garden that has a green roof for the purpose of extending their horticultural endeavors will find no labor in visiting the green roof on a more regular basis to sustain the own fulfillment through gardening.


Green Roof Maintenance

About SED Design

The award winning firm SED DESIGN is dedicated to the design of distinctive and evocative spaces in the context of the regional landscape.   The firm’s public landscapes and private gardens integrate low impact and green principles of sustainability with the programmatic needs of each individual client.


The firm’s landscape architects bring innovative solutions to produce memorable work that contributes to environmental health by restoring life sustaining processes that improve the quality of our earth, air and water.   Basic to this work is the development of a scientific and aesthetic understanding of each site.    Study and evaluation of environmental conditions and natural systems, cultural influences and historical uses, as well as user needs are essential to this understanding.   The firm uses research and analysis to reveal the inherent and unique qualities of each site to inform and enhance the design process.


Teaching Background

From 1990 to 2002 Edgar David, founder of SED Design, served as a tenured Professor of Landscape Architecture in the Department of Landscape Architecture and Horticulture at Temple University where he taught courses in field ecology, landscape restoration, ecological management, and landscape architectural design.