It’s finally official and I can stop worrying. The permits have come through for building a green roof on my front porch.  

Another bit of good news: The Anacostia Watershed Society has informed me that I will receive the $5 per square foot rebate they help administer for the District Department of the Environment. So DC Greenworks, the nonprofit building the green roof, has gathered the materials and plants, and we will start the installation soon if the weather holds.

In the meantime, I have investigated whether my small (150-square foot) green roof qualifies me for a discount in my monthly District Department of the Environment (DDOE) stormwater fee or in D.C. Water’s Clean Rivers Impervious Area Charge (CRIAC); these fees are applied to residential and commercial property owners through the D.C. Water bill. 

Though the fees address different pollution and stormwater control systems, both are based on a property’s square footage of impervious surfaces (roofs, concrete sidewalks, parking lots).  Impervious surfaces cause stormwater to run off into the District’s storm drains instead of soaking into the ground.  This increases flooding and the amount of stormwater that D.C. Water and the District have to manage.  

A green roof can decrease stormwater runoff from a roof by up to 50 percent annually, according to a 2009 EPA Report, and I had heard through DC Greenworks that I may be able to get a discount in impervious surface-related fees, especially in the future when costs go up.  

For DC Water’s CRIAC, customers are charged about $6.64 per month for every “Equivalent Residential Unit” (ERU) of impervious surfaces (an ERU is based on the median amount of impervious surfaces on residential properties, roughly 1,000 square feet).  The basic charge for the District stormwater fee is $2.67 per ERU per month.  However, these charges have been modified for residential customers using a six-tier rate structure. (For more information on this rate structure, click on “How is the stormwater fee calculated?” at the District Department of the Environment Web site; a similar table is available on the DC Water CRIAC Web site). 

Going online, I learned that D.C. Water calculates my impervious surface area as 1,210 square feet, which means I am charged a little less than $10 a month for the two fees combined.  However, in the future, it’ll be much more: one projection for the CRIAC alone is $32 per month per ERU by 2020.

At first, I thought that any discounts would be based on a green roof effectively decreasing the amount of impervious surface area on my property, i.e., reducing my ERUs. But according to Eric Hunt of D.C. Water and Emily Rice of DDOE, a green roof is still over an impervious surface, and if not maintained, stormwater runoff could return to impervious surface levels.  The impervious surface has to be removed for a reduction in ERUs.  Even if it had, factoring in my 150-square foot green roof would not have brought me down to the next tier rate (which is below 700 square feet).

Annette L. Olson's rain garden, installed in 2010 through D.C.'s Riversmart Homes program. (Photo by Annette L. Olson)

For instance, the DDOE is preparing rules to provide up to a 55 percent discount on the stormwater fees. (This is a discount applied to the fee once assessed; it is not a reduction in ERU).  According to DDOE, once the “RiverSmart Rewards” program starts accepting applications, any discount awarded should be retroactive to May 2009 or to the date of installation, whichever is later.  Details on the D.C. Water program are still being determined, but it is anticipated it will launch in 2014.

We’ll have to see when this happens, and the amount for which I’ll qualify.  I won’t be receiving any discounts for now, which is a letdown, but I look forward to them in the future. 

Of course, I need to get the green roof built first, which should happen soon if all goes well.

 Read more about Annette L. Olson’s green roof installation

Annette L. Olson is a Petworth homeowner who will share her experience of installing a green roof on her row house.