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Frequently Asked Questions About Roof Gardens


What do I need to know about my building to consider a roof garden installation?

You will need to know the slope, the structural loading capacity, and existing materials of the roof, as well as the nature of any drainage systems, and waterproofing. You should also consider what kind of sun and wind exposure the roof gets.

How much does a roof garden weigh?

The average Extensive Green Roof (3"-4" of growing medium ) weighs 28-30 lbs per square foot fully saturated. Intensive green roofs (4" and up) can weigh up to 100 lbs per square foot depending on the depth of the growing medium.

What are the first steps for designing and estimating a roof garden?

Measure the approximate square footage of your roof. Determine the age and type of your roof’s waterproof membrane. A green roof requires a new or recently replaced (1-5 year old) waterproof membrane. Locate the building plans that provide the structural information of how much weight your roof can withstand? If not, you will need to hire a structural engineer.


Where can I find details on Tax Incentives?
New York State currently provides a property tax incentive for building owners who install a roof garden that covers 50% or more of their building's roof. The Department of Buildings provides further details about this incentive, and also has a list of frequently asked questions and answers located here.

 

Can people walk on the roof garden?
Normally, extensive roof gardens are not designed for pedestrian traffic. Occasional foot traffic by a maintenance worker would not be a problem for most commonly used plants.

What happens to my roof garden in the winter?
The appearance of your roof garden depends on your location and the plants selected. The majority of sedums are evergreen and will turn dark and go dormant in the winter. Grasses will go dormant and look brown all winter but then will regenerate new growth in the spring.

What will my roof garden look like in the winter time?
A roof garden can be designed to be evergreen or deciduous in accordance with the preferences of the client. There are always trade-offs between summertime beauty and winter foliage. Many deciduous plants will offer bright and extensive summertime blossoms, while evergreen plants might be more subdued.


What about sloped roofs?
In Germany, there is experience with green roofs of up to a 45 degree pitch. The complexity increases with pitch; as soil baffles, drainage, and other considerations must be designed.


How many LEED credits can I receive?
Roof gardens can facilitate a significant improvement in the LEED rating of a building, contributing as many as 15 credits under the system, depending on design and level of integration with other building systems. In some instances, while green roofs may not contribute directly to achieving points under the system, they contribute to earning LEED credits when used with other sustainable building elements. For example, roof gardens can earn direct credits under the following:

  • Reduced Site Disturbance, Protect or Restore Open Space
  • Landscape Design That Reduces Urban Heat Islands, Roof
  • Stormwater Management
  • Water Efficient Landscaping
  • Innovative Wastewater Technologies
  • Innovation in Design

Is a roof garden more likely to leak than a regular roof?
This is one of the most misunderstood issues surrounding green roofing. A roof garden must be installed over a roof that has a waterproofing membrane that is in excellent condition. A high quality waterproof membrane will protect your building or home against leaks. Adding a roof garden will more than double the life of your membrane. This is possible because the roof is protected from damaging UV rays as well as the constant heating and cooling cycles which cause expansion and contraction leading to cracks in your membrane over time.


How do roof gardens interact with photovoltaic panels?
Roof gardens and photovoltaic panels are complementary technologies that improve each other's performance. The PV functions more efficiently thanks to the cooler ambient temperatures above the roof garden, and the roof garden benefits from the areas of shade.


How does a roof garden help in terms of sound insulation?
It has been proven that roof gardens can insulate up to 3dB for internal sound insulation, and up to 8dB for reflective sound. The layers of the green roofing system help to provide insulation of sound waves. This benefit is most valuable for buildings near airports, highways, or heavy machine activity.


What is roof garden growing media?
Roof garden growing media can be defined as an engineered soil that both mimics and improves on the properties of natural soil. Native or natural soil is the product of a natural process that has occurred over thousands of years. Although native soil works perfectly in its natural environment, it cannot be used on roofs due to its excessive weights, its inability to retain sufficient amounts of moisture, as well as its inability to drain excessive amounts of moisture properly.

Roof garden growing media faces several additional requirements since it ultimately must promote plant life in an environment which is very different from the natural surroundings of these plants. Growing medium should support plant growth, be lightweight, and should retain and drain water simultaneously. It also must perform all of these functions in an extremely shallow system.


How does roof garden media differ from 'soil'?
Conventional green roofing media is mostly light-weight mineral material, with a minimum of organic material. It should be designed to meet established FLL guidelines for both water retention and drainage. One the most important criteria for media is that it remain a viable growing and water-control substrate for decades.
 

Can recycled materials be used in constructing roof gardens?
Using recycled materials is an important goal in the roof garden industry. Currently components containing recycled materials are available and used in the LiveRoof® and GreenGrid® tray systems that we install.
 

How can growing media be conveyed to the roof?
Main transportation devices for roof growing media products onsite are cranes, conveyor belts, or blower trucks. Many factors have to be considered in order to find the best option for a specific project including height and size of the building, accessibility of the roof, size and design of the roof garden as well as other criteria which can influence onsite transportation. Onsite transportation of green roofing media is a crucial factor for calculating costs of roof garden installation.


How do roof gardens affect wildlife?
New developments lead to a loss of habitats – roof gardens can contribute to biodiversity and address local biodiversity action plans. In particular they have been shown to favor many rare invertebrates found on brownfield sites, as well as ground-nesting birds such as skylarks.
 

Contact us for a free consultation.

 
27 Greenwood Ave.
Midland Park, NJ 07432
Ph: 201-447-6205
E: service@rscape.com

We serve the following New Jersey locations:
Bergen County, Ridgewood, Wyckoff, Saddle River, Upper Saddle River, Glen Rock, Midland Park, Franklin Lakes, Fair Lawn, Ramsey, Mahwah, Ho-Ho-Kus, Hawthorne, Allendale, Oakland, Paramus, Waldwick, Woodcliff Lake, and more.
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