SS 4.3 – Management of Runoff from Roof

green roof

Oh, this is a timely posting.  What is interesting here is that all the LEED requirements are design and build requirements; now that we have lived in our house for a little over a year, we can see if what we planned to happen is indeed the case.

Water runoff from the roof in a storm can be a huge problem.  Where does it go?  We have a flat roof.  The initial design of our house had internal drains — so our roof was designed to pitch inward, and the internal drains would go through the house and out somewhere to drain.  That was not only quite expensive, but it scared me!  In one of our cost-cutting exercises, we changed from internal drains to external scuppers and downspouts, with the whole roof pitched slightly to the west.  Now at least we can see the water coming off our roof — and it stays outside.

For a maximum of two points, we need to design and install one or more of the following runoff control measures:

a. Install permanent stormwater controls (e.g., vegetated swales, on-site rain garden, dry well, or rainwater cistern) designed to manage runoff from the home (1 point).

b. Install vegetated roof to cover 50% of the roof area (0.5 point).


c. Install vegetated roof to cover 100% of the roof area (1 point).

d. Have the site designed by a licensed or certified landscape design or engineering professional such that all water runoff from the home is managed through an on-site design element (2 points).

We actually do have a vegetated roof — we call it a green roof — made up of different varieties of sedum, but it covers less than 50% of the roof.  Initially we wanted that a green roof everywhere (I love the thought of a bird above not knowing there is a building below), but it did not make sense from a cost or maintenance perspective.  The only green roof areas we have are those that we can see from our house — the breezeway connecting the house to the garage/office, and half of the top of the garage which I can see right now from my office.  So no points in (b) or (c).

We did, however, have a landscape professional design the site to manage runoff from the roof.  The top of my office drains onto the green roof, so that area is managed.  On the house, there are two downspouts, each draining into a 24″ catch basin.  Under those catch basins are more drainage design elements: on the south side, a drain tile carries the water to a vegetated swale along our property line (naturally occurring); on the north side, it goes to a perforated sleeve that slowly releases the water underground where our wildflower garden rests.  Our design professional, Travis, signed the accountability form, so that is all we have to submit for 2 points here.

Did it cost more to get these points?  I think we would have done these measures regardless of LEED, because the water running off the roof needs somewhere to go other than our foundation and basement.  It’s an important durability requirement, and I’m glad it was addressed!

Now, onto what has really happened.  We have had so much rain this summer, we are really testing the systems.  The drain tile to the north had been slightly crushed by our entryway pavers.  It so happens that we also have a PVC pipe that runs into our crawl space that carries the electric cord to power our irrigation well pump.  That pipe also got slightly crushed by the pavers in our entryway.  A double-whammy that resulted in HUGE amounts of water gushing into the crawl space — water from the roof pouring into the PVC pipe.  Luckily, the times this has occurred we have been here AND noticed it; we needed two adults hauling 13-gallon buckets in and out of the crawl space, causing backaches for days.  Also luckily, we found where the pipes were broken and corrected everything.  We have another slight issue on the south side, but that’s another story.

Sustainable Sites points so far: 10

Cumulative points: 24

Additional points needed to get to Gold: 64

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