Green Roofs

Does the roof need to be flat?

There is no such thing as a flat roof. All roofs have some slope to the drains to eliminate rain water The ideal slope for a green roof is between one-eighth and one-quarter inch per 12 inches. A green roof can be sloped up to 40 percent, requiring slope stabilization systems to keep components from sliding off.

Can you earn LEED credits for building a green roof?

Yes! But not directly. Green roofs can contribute to LEED credits in the following categories of the USGBC’s green building rating system: PART 1: Sustainable Sites Reduced Site Disturbance, Protect or Restore Open Space Reduced Site Disturbance, Development Footprint Credit Landscape Design That Reduces Urban Heat Islands PART 2: Water Efficiency Storm Water Management Water Efficient Landscaping Water Use Reduction Innovative Wastewater Technologies PART 3: Energy and Atmosphere Optimize Energy Performance Renewable Energy CFC and Ozone Depleting Substance Reduction PART 4: Materials and Resources Storage and Collection of Recyclables Recycled Content Materials PART 5: Indoor Environmental Quality PART 6: Innovation in Design Presently, the only widely-accepted, established standards for green roof construction are those developed in Germany by the Forschungsgesellschaft Landschaftsentwicklung Landschaftsbau.… Read More

How long does a green roof last? Does a green roofs last as long as a traditional roof?

Green roofs result in extended life expectancy of a roof. Based on 50-plus years of experience with green roofs in Germany where green roofs are common, a green roof can be expected to experience double or triple the life of a standard roof. How does this work? Green roofs provide protection of the waterproofing membrane from wind-blown debris and shielding from damaging UV radiation which is increasing due to climate change. Green roofs provide impressive insulation from temperature extremes, thereby minimizing damage from daily expansion and contraction. Because green roofs last longer, they reduce construction waste in landfills because they do not have to be torn down and replaced as often.… Read More

How much does a green roof cost?

Cost per square foot depends on many factors: the size and slope of the roof, depth and complexity of the system, height and accessibility from the ground, cost of labor, and need for specialized elements, such as drains, railings, pavers, slope stabilization measures, etc. Prices range from $25 per square foot to $45 per square foot. A typical small residential project tends to be on the higher side of the range.

What kind of maintenance does a green roof need?

After the initial two years it takes for plants to become established, most extensive green roofs in climates receiving regular summer season rainfall only need weeding, and occasional infill transplanting, twice a year. In dry climates such as Southern California, green roofs need supplemental irrigation between March and late November. Good Earth Plant Company can take care of all the these needs of your green roof through our maintenance program. We check all of the drains, inspect the roof for any indications of a potential penetration and leak, prune as needed, remove weeds and other debris, lightly fertilize per schedule and check and adjust the irrigation system.… Read More

Can a green roof catch fire and spread fire?

Not if the green roof is designed correctly. In Germany, green roofs actually have a better fire rating than conventional roofs because the mineral media layers cannot burn. The extensive use of sedums (a type of succulent) in Europe, the northern United States and southern Canada, as well as gravel borders and breaks also protect against fire. In our arid, fire-prone Southern California region, we engineer the system with fire-retardant features, paying special attention to mineral content, gravel layers, and plant selection.

Why is drainage important for a green roof?

“Ponding” on your roof is never a good thing. The additional weight and the tendency of water to find its way through waterproofing requires all roofs to completely drain. Proper drainage ensures the growing medium will be maintained in an aerated condition suited t healthy plant growth. Basal drainage must also be designed with large rainfall events in mind. The goal is for all rainfall to percolate to the base of the green roof system. Any water NOT absorbed should move ‘underground’ through a drainage layer toward roof drains or scuppers, and then into your rainwater harvesting system (if installed). City codes typically require a redundancy in your drains or scuppers, just in case something clogs them up.

What if the roof leaks?

Fixing a leak under the green roof is relatively easy. Finding it is the hard part. Surprisingly, leaks in the waterproofing layer are less likely when it is protected from the elements by a green roof. If a leak does occur, it can readily be located through new electronic technology, such as electric field vector mapping (EFVM), which can rapidly and accurately pinpoint even minute holes. While Good Earth Plants implements flood testing prior to the installation of plants and growing media, the addition of an EFVM system is convenient, need not be installed in advance, and can even be used on steeply-sloped surfaces.… Read More

What kind of waterproofing do I need?

Many types of waterproofing are compatible with green roofs. We like single ply roofing systems that are like pond liners making the roof one giant, shallow, planter. World-wide, polyvinyl chloride (PVC) and polymer modified bituminous membranes are the most common. Many of these installations have now been in place for over 30 years and continue to perform as designed. PVC, EPDM and thermal polyolefin (TPO) are, in most cases, inherently root-resistant; other common waterproofing materials require a root barrier between the waterproofing materials and the vegetated cover.

How does a green roof affect the conventional roof below it?

Based on German experience, a green roof can be expected to double or triple the life of the underlying conventional roof by protecting from human activity and wind-blown debris; shielding from UV radiation; and buffering temperature extremes, thereby minimizing damage from daily expansion and contraction.