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It appears that Washington DC has a green roof rebate program where I can get $15/sq.ft to install a green roof.

Green roofs are stormwater management practices that capture and store rainfall in an engineered growing media that is designed to support plant growth. A portion of the captured rainfall evaporates or is taken up by plants, which helps reduce runoff volumes, peak runoff rates, and pollutant loads on development sites. Green roofs typically contain a layered system of roofing that is designed to support plant growth and retain water for plant uptake while preventing ponding on the roof surface. The roofs are designed so that water drains vertically through the media and then horizontally along a waterproofing layer towards the outlet. Extensive green roofs are designed to have minimal maintenance requirements.

I like the idea of being environmentally friendly and storm water run off is a major issue. I am a little worried about minimal maintenance as I don't have access to my flat roof and do not like the idea of climbing a 35 foot ladder with gardening supplies.

What type of maintenance is typical of a well designed green roof?

Bamboo
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StrongBad
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  • Well, wow. In Oregon it is against the law to collect rainwater from our roofs to use for anything. I also know about 'percentage of permeability'...where raw soil is 100% (ha ha ha), gravel is half that in percentage, decks and concrete are zero percentage. Our urban centers are horribly excluding water from the water table. There are also very strict rules that insist one has x percent permeability on their property. I've not heard of this Green Roof till now. Sure sounds like they are making home owners responsible for run off to fix their screw ups for storm water drainage. – stormy Aug 16 '18 at 20:15
  • @stormy they also subsidize [rain barrels](https://doee.dc.gov/service/rain-barrel-rebates). As DC is a swamp (in more ways than one) with considerable rain and lots of impermeable surfaces runoff is a major issue. – StrongBad Aug 16 '18 at 20:19
  • I've been talking to these guys in D.C. They are trying to mitigate a problem they set up with no specs on permeable surfaces. Their cross section shows a great way to cause a perched water table. Here in Oregon it is illegal to have rain barrels! D.C. needs to get a program for making impermeable surfaces into permeable surfaces, not worrying about making roof top gardens. Though that works, but is expensive to do! The city screwed up big time with permeable surfaces! Their specs for roof gardens is not at all workable. Great for mosquitoes however! – stormy Aug 16 '18 at 21:46
  • Add mycelium to the roof, as it will help with remediation of the storm water. – black thumb Aug 17 '18 at 04:16
  • What weight is your roof rated to carry? What sort of roof structure is it? – Graham Chiu Aug 18 '18 at 04:28

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Where I live there are long hot summers and winters with alternating melt and freeze cycles. The green roofs that work are the ones that receive regular weeding and replanting. Surprisingly you might have to water your roof during a prolonged hot dry spell. If plants die out weeds will move in.

Here are two roofs

Roof of the War Museum, Ottawa : still looks good after many years War Museum Ottawa

Algonquin College: as built Algonquin College

and as it looks now after a hot summer with, apparently, no maintenance Algonquin College aerial view

Here is a visual of a typical installation. A lot of preparation required green roof schematic

You asked:

What type of maintenance is typical of a well designed green roof?

  • monthly weeding
  • annual planting in the spring to fill in dead spots or rejuvenate the medium
  • watering during droughts

What is needed is easy access to do this. Slanted roofs are a problem to get to but good to drain water off.

kevinskio
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