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Green Roof Coverage

Green Roof Coverage Rate

Coverage rate is the percent of media covered by vegetation. Our stewardship team scores each living roof’s coverage rate on each visit. This page illustrates and describes coverage rates to clarify terms and set expectations.

 

 


Vegetative Cover Diagrams

Vegetative coverage is typically “measured” using the naked eye, but this requires a trained eye. The diagrams below illustrate the optical illusions between coverage that is evenly and randomly distributed, versus coverage that is un-evenly and randomly distributed. Although vegetative coverage is measured in plan view (looking straight down on the green roof), most people experience the green roof in perspective, which further complicates accurate coverage scoring. In perspective, taller plants may appear to provide more coverage than they do, and shorter plants may appear to provide less coverage than reality.

 


 


 

 



Green Roof Vegetative Coverage: 95-100%

The very high green roof coverage rate of 95-100% may be difficult to sustain long-term without high inputs such as excessive fertilizer, irrigation, or supplemental plants. This very high coverage rate is often found in pregrown mats and pregrown modules, where such plant ‘overcrowding’ may occur due to high fertilizer and irrigation at the nursery; these can be expected to stabilize around 90-95% coverage as they mature.

95% green roof vegetative coverage
95% green roof vegetative coverage

 
Very High Living Roof Plant Coverage

95-100% Green Roof Vegetative Coverage: A newly installed pregrown green roof.

 
Very High Vegetated Roof Plant Coverage

95-100% Green Roof Vegetative Coverage: A newly installed pregrown green roof.

 
Green Roof Very High Plant Coverage

95-100% Green Roof Vegetative Coverage: Closeup of new pregrown modules at approximately 100% coverage.

 



Green Roof Vegetative Coverage: 90-95%

A coverage rate of 90-95% is a very sensible goal for living roof stewardship. This coverage rate is full and lush, but avoids overcrowding, and has enough open space to accommodate ebbs and flows endemic to green roof ecosystems. Green roofs planted with cuttings and plugs should reach 90% coverage within 1-2 years of planting.

95% green roof vegetative coverage
95% green roof vegetative coverage
90% green roof vegetative coverage
90% green roof vegetative coverage

 
High Living Roof Plant Coverage

90-95% Green Roof Vegetative Coverage: A healthy green roof with spring blooms of Sedum sexangulare. The few open spaces will close as summer approaches.

 
Vegetated Roof High Plant Coverage

90-95% Green Roof Vegetative Coverage: Another healthy green roof with spring blooms of Sedum sexangulare. The few open spaces will close as summer approaches.

 
High Green Roof Plant Coverage

90-95% Green Roof Vegetative Coverage: This is the same pregrown module green roof shown 4 photos up, the spring coming out of its first winter. Notice many hardy plants with great coverage; the few open areas are where the less hardy species did not survive winter, nature’s way of removing overcrowding.

 
Living Roof Plant Coverage Pregrown

95-100% Green Roof Vegetative Coverage: An EcoCline 3+1 green roof with approximately 95% cover one year after installation with pregrown mats

 
Vegetated Roof High Plant Coverage

90-95% Green Roof Vegetative Coverage: Closeup of green roof vegetation with 90-95% overage

 



Green Roof Vegetative Coverage: 80-90%

Green roofs in this category appear full, have a substantial vegetative cover to stabilize media, and still have room to grow. Green roofs with 90%+/- vegetative cover in summer may drop to 80%+/- cover in winter, which is normal for the herbaceous plants used in extensive green roofs.

90% green roof vegetative coverage
90% green roof vegetative coverage
85% green roof vegetative coverage
85% green roof vegetative coverage
80% green roof vegetative coverage
80% green roof vegetative coverage

 
Living Roof Plant Coverage

80-90% Green Roof Vegetative Coverage: This beautiful, blooming green roof has about 80% coverage. Plant height and the angle of the photo cause it appear to have about 90% coverage, but 80% is more accurate, as coverage is measured looking ‘straight down’.

 
Vegetated Roof Plant Coverage

80-90% Green Roof Vegetative Coverage: This healthy, low-growing green roof has around 90% coverage.

 
Green Roof Plant Coverage

80-90% Green Roof Vegetative Coverage: A 1-year-old young EcoCline R+2 green roof, with approxmately 85% coverage. Planted via cuttings.

 
Living Roof Plant Coverage

80-90% Green Roof Vegetative Coverage: Closeup of the same young EcoCline R+2 green roof as above, with approxmately 85% coverage. Sedum sexangulare is taking root in the large aggregate media and will soon narrow the gaps in exposed media.

 



Green Roof Vegetative Coverage: 60-80%

Green roofs with vegetative cover at 60-80% are “getting there”. This “not-quite-full” coverage rate is normal in the first year or two while plants establish healthy root systems to build resilience. Sometimes a living roof with as high as 95% cover may experience a late-summer, drought-induced coverage drop to 60-80%, as the Sedums self-prune as a drought survival mechanism; this is nothing to worry about. Vegetated roofs planted with cuttings and plugs may reach 60-80% coverage within one year, though plants may be short in the first year.

80% green roof vegetative coverage
80% green roof vegetative coverage
70% green roof vegetative coverage
70% green roof vegetative coverage
60% green roof vegetative coverage
60% green roof vegetative coverage

 
Living Roof Plant Coverage

60-80% Green Roof Vegetative Coverage: This beautiful, blooming green roof has about 70% coverage. Plant height and viewing angle make it appear to have about 85% coverage, but 70% is more accurate, as coverage is measured looking ‘straight down’.

 
Vegetated Roof Plant Coverage

60-80% Green Roof Vegetative Coverage: From this aerial vanatage point, we can easily see that this vegetated roof has approximately 70% coverage. Note that the coverage consists of red and yellow foliage, in addition to green.

 
Green Roof Plant Coverage

60-80% Green Roof Vegetative Coverage: This young green roof has approximately 70% coverage, consisting of many short, evenly distributed plants.

 
Living Roof Plant Coverage

60-80% Green Roof Vegetative Coverage: Closeup of vegetative coverage in the 60-80% range. This evenly distributed appearance is similar for cuttings filling in after approximately 1 year, or for pregrown mats in the midst of acclimating from the nursery to the harsher rooftop.

 



Green Roof Vegetative Coverage: 40-60%

Vegetative coverage of 40-60% is usually achieved when cuttings or plugs have grown for a few warm months. A vegetated roof planted via cuttings and/or plugs may reach 60% coverage as soon as 3-4 months after planting, or within one year of planting, depending upon season planted, weather, density of planting, species used, and other environmental conditions. A green roof should not be at this coverage rate for very long.

60% green roof vegetative coverage
60% green roof vegetative coverage
50% green roof vegetative coverage
50% green roof vegetative coverage
40% green roof vegetative coverage
40% green roof vegetative coverage

 
Living Roof Plant Coverage

40-60% Green Roof Vegetative Coverage: An EcoCline green roof two months after planting with cuttings and plugs.

 
Vegetated Roof Plant Coverage

40-60% Green Roof Vegetative Coverage: A green roof, planted with plugs, just starting to fill in.

 
Green Roof Plant Coverage

40-60% Green Roof Vegetative Coverage: A green roof, planted with plugs, just starting to fill in.

 
Living Roof Plant Coverage

40-60% Green Roof Vegetative Coverage: Closeup of vegetative coverage in the 40-60% range. This photo shows plugs soon after planting at a relatively high density of approximately 3 plugs per square foot.

 



Green Roof Vegetative Coverage: 20-40%

Coverage jumps upward from 20% into this category when cuttings and plugs establish roots into the surrounding media and start to grow. When the living roof reaches this level of coverage, we can be sure that the plants have taken hold, and the next steps are encouraging growth and spread to reach higher coverage rates. The green roof should not be in this category for long.

40% green roof vegetative coverage
40% green roof vegetative coverage
30% green roof vegetative coverage
30% green roof vegetative coverage
20% green roof vegetative coverage
20% green roof vegetative coverage

 
Living Roof Plant Coverage

20-40% Green Roof Vegetative Coverage: An EcoCline green roof just after newly spread cuttings begin to grow.

 
Vegetated Roof Plant Coverage

20-40% Green Roof Vegetative Coverage: A green roof planted with 1-2 plugs per square foot, after approximately one warm month of growth.

 
Green Roof Plant Coverage

20-40% Green Roof Vegetative Coverage: A green roof, planted with plugs, just starting to grow.

 
Living Roof Plant Coverage

20-40% Green Roof Vegetative Coverage: Closeup of an EcoCline green roof, planted with cuttings just starting to grow.

 



Green Roof Vegetative Coverage: 0-20%

Just after planting plugs, or within a few weeks of planting cuttings, a green roof should have approximately 20% coverage. This is the look of a brand new “baby” green roof ready to grow.

20% green roof vegetative coverage
20% green roof vegetative coverage
10% green roof vegetative coverage
10% green roof vegetative coverage

 
Living Roof Plant Coverage

0-20% Green Roof Vegetative Coverage: This newly installed green roof has approximately 10-15% coverage immediately upon planting via plugs.

 
Vegetated Roof Plant Coverage

0-20% Green Roof Vegetative Coverage: This newly installed green roof has approximately 15% coverage with new cuttings emerging.

 
Green Roof Plant Coverage

0-20% Green Roof Vegetative Coverage: This newly installed green roof has approximately 15% coverage with new cuttings emerging.

 
Living Roof Plant Coverage

0-20% Green Roof Vegetative Coverage: Closeup green roof media with cuttings and seed just sprouting, with approximately 10% coverage.

 



Green Roof Vegetative Coverage: 0%

The only time a green roof should have 0% coverage is before planting.

Green Roof Plant Coverage

0-20% Green Roof Vegetative Coverage: The only green roofs that should have 0% vegetative coverage are those still under construction.