Green roofs have several environmental benefits. In addition to improving air quality, saving
energy and reducing the urban heat island effect, green roofs benefit water quality by absorbing
water during small storms and slowing runoff during large storms. Green roofs of all sizes can be
incorporated into the home landscape as part of a sustainable rainwater landscape design.

Green roofs block water. Planted roofs trap rainwater from small storms, absorb it as it falls, and
then release it as transpiration. Trapping rainwater in this way helps prevent flooding downstream
by mimicking the natural state in which plants absorb and release water. Shallow green roofs can
completely block out rainwater when rainfall is less than an inch at a time. This reduces stormwater
runoff loads on water bodies downstream of our home.

This green roof in Pittsburgh features six varieties: Sedum, Allium and Talinum.

Green roofs slow down runoff. In addition to stopping small storms, green roofs filter and buffer
water during long, intense rainfall periods. It takes longer for water to travel through the plantation
layer and other media on a green roof compared to a traditional roof where the water flows right
through and stirs up the roof gutters and spouts. Lowering runoff allows water to return to the
aquifer at a slower rate and reduces downstream flooding.

Green roofs reduce stormwater runoff loads on other systems. In home landscaping, rooftops
can occupy more than 40% of a building’s area. Implementing a green roof on the site means that
much of the stormwater runoff can potentially be intercepted before reaching the impermeable
areas of the site. It also reduces the load on other sustainable systems that may be used, such as
rain gardens and permeable pavers.

Green roofs stop dirty spills at their source. When comparing a roof without plantation to a
green roof, the effect on rainwater is evident. A roof devoid of plantation is a large surface area
where water can drip and drip off quickly.

There are two problems with unvegetated roofs. Water falls on the roof and drains very quickly.
Think of how quickly water drips from a roof into a downspout during a heavy rain. This rapid
runoff is a big problem in urban environments with more impervious surfaces because it increases
downstream flooding. In the event of a small rainstorm, living roof plants trap rainwater and
release it back into the atmosphere through transpiration and evaporation. The rhizosphere and
growing medium also absorb some of the water. And during severe storms, green roofs slow down
water that cannot be absorbed directly.

The second problem is that the unvegetated roof has a dirty surface. This is because air pollutants
regularly build up on rooftops. When it rains on a dirty rooftop, all contaminants are quickly
washed away and carried downstream. Green roofs stop these problems at the source by storing
carbon dioxide and blocking airborne particles.

More:
How to install a green roof https://kdroofers.com
How to manage rainwater in your landscaping https://kdroofers.com