A climate-adapted green roof is a green roof that performs resiliently in its specific location. This means that vegetation, soil, retention, and drainage all perform optimally. No one green roof profile can be expected to perform optimally in every climate and building microclimate. When choosing or designing a green roof profile, but sure the green roof is climate-adapted.
Dry climates, wet climates, cold climates, sweat climates!
Green roofs are often sold like manufactured products: One-size-fits-all. But unlike most manufactured products, green roofs interact intimately with natural forces: absorbing water, receiving sunlight, evaporating into the atmosphere, etc. Since each climate zone may have a unique combination of rainfall, sunlight, wind, temperature, and humidity, the green roof should be designed accordingly.
|Annual Rainfall||2-Year, 24-Hour Storm Size||Temperature Profile||Warm Season Nightly Temperature Profile||Primary Green Roof Challenges|
|Baltimore, MD||114cm (45 inches)||~9cm (3.5 inches)||Temperate, four seasons, moderate winters||Moderate summer nights||Ability to handle repeat storms; ability to span droughts in summer|
|Cleveland, OH||99cm (39 inches)||~6cm (2.5 inches)||Temperate, four seasons, cold winters||Moderate summer nights||Sustaining moisture levels|
|Denver, CO||30cm (12 inches)||~4cm (1.5 inches)||Hot summers, long winters||Sustaining moisture levels; extreme drought tolerance|
|Atlanta, GA||234cm (92 inches)||~10cm (4 inches)||Hot summers, short wet winters||Hot summer nights||Ability to handle repeat storms; ability to span droughts in summer; support non-Sedum plants|
|Singapore||234cm (92 inches)||Tropical||Moderate summer nights||Ability to handle repeat storm events; high demand on proper drainage|
In the examples above, there are two extremes: Denver and Singapore, one with hardly any rain, and one with some of the highest rainfall volume on the planet. These two locations obviously have different criteria.
But look again at Baltimore versus Cleveland. Most of us humans might consider Baltimore and Cleveland to have a similar climate, except Cleveland, usually gets more snow. But plants are more sensitive to some environmental differences than we humans are. Cleveland receives about 15cm (6 inches) less rain annually than Baltimore; further, the 2-year/24-hour design storm for Baltimore is about an inch higher than it is in Cleveland. This effectively means that in Baltimore, there is a higher need to manage larger storms and back-to-back storms, and in
Now let’s compare Baltimore and Atlanta. Atlanta certainly has hotter summers and milder winters; those facts influence our plant selection a little bit. Both locations have similar annual rainfall volumes and 2-year 24-hour design storms, so there are not many differences needed in profile selection due to that. But look at the differences in summer nighttime temperatures. Baltimore usually has fairly mild nighttime summer temperatures (say around 21°C [70F] on a 32-38°C [90-100F] day) but Atlanta often has hot nighttime summer temperatures (say over 27°C [80F] on a 32-38°C [90-100F] day). This turns out to be the most demanding climate difference.
Why do nighttime summer temperatures matter? In short, Sedum plants require relatively cool nighttime temperatures to respirate. Read more about it here. So in Atlanta, we will need to find plants other than Sedum, which probably means that the thickness and weight of the green roof profile is not determined as much by stormwater concerns as it is by plant survivability concerns, or that we need a profile that will manage water and surface temperatures in a way that provides nighttime cooling.
We hope this makes it clear why any single profile cannot be expected to perform optimally in all locations.