Green roof - no irrigation system but manual watering during hot summer months - relevant?

You are allowed to provide temporary watering during the establishment period for the green roof, and you are allowed to provide manual watering in an unusually dry season or drought. However, if your normal summer would require watering, whether by hand or by irrigation, that doesn't meet the credit requirements for "no irrigation." 

We have a similar situation in our region - 9 months of drizzle and rain, and a summer with very little rain. When there's a green roof that requires summer watering, we've only earned Outdoor water use reduction - no irrigation by using non-potable water for irrigation or a rainwater harvesting system with a large enough cistern to get through the whole summer. 

True, the US EPA water budget tool and the LEED Outdoor water use calculators will tell you how much water is needed for your green roof design when you select a particular irrigation type. But since watering by hand to get through a normal season doesn't meet the requirements of no irrigation, so you'll need to follow Option 2, Reduced Irrigation. It won't be easy to demonstrate a 30% reduction from the baseline of typical watering amount since there's no way to calculate how much water would be provided by hand watering.

Hand watering could easily use more water than an irrigation system. If it's done during a hotter time of day some of the water would evaporate; it's hard to determine if you are over- or under-watering, and it's hard to consistently provide different watering amounts for different planting zones. Drip irrigation systems with moisture sensors, timer controls, and zones for different plant types address these issues.      

There are usually two ways to reduce the outdoor water use for irrigation: selecting plants that need less water, and a more water efficient irrigation system. One possibility would be to use the same irrigation type in both your baseline and proposed design such as fixed spray, and try to earn the 30% reduction by using plantings that need less water than a baseline design.   

Since this is a pre-requisite, you might want to reach out to USGBC customer service for guidance. Does that all make sense? 

In terms of manual watering; what irrigation type should be selected in the EPA water budget tool ? Our project is featuring most of the landscape area not requiring irrigation (auto or manuel), except for a few rooftop planters that will need manual watering during normal summer months.  

Hi Priscillia,

There is no info for manual or hand watering in LEED guide or submittal tips. It seems like hand watering is not considered as type of irrigation allowed in LEED.

You might consider changing the plant type for rooftop planters to those that require no irrigation so your project will not require irrigation at all and can meet "no irrigation" credit requirement and earn 2 points.