Green Roofs - Living Architecture Monitor - Spring 2014 - (Page 24)

PROJECT PROFILE BIG BOX RETAILERS EMBRACING GREEN ROOFS? THE CLIENT SPEAKS!-WALMART OPENS UP ABOUT THEIR GREEN ROOF LIFE CYCLE COST-BENEFIT ANALYSIS, THE IMPORTANCE OF SUPPORTIVE POLICY AND MORE the data suggests it would save 1-6% storewide in a range of climates, with a 2.2% savings estimated in Chicago. Roof temperatures were up to 40 degrees cooler during hot weather on the green roof, but savings from the green roof were greater in cold weather than in warm weather. Summer savings would be higher if the basis for comparison was a black roof rather than a white one, but Walmart builds new stores in the United States with white roofs. The green roof has an added benefit of peak load shifting due to its thermal mass. This study is one of the first to also demonstrate that the green roof moderates air temperature at rooftop HVAC unit intakes. This translates to air conditioning savings in summer, as well as heating savings in winter. Stormwater Stormwater retention and peak rate attenuation are two important criteria affecting city storm sewer capacity and water quality in lakes, rivers and bays. This study showed that a green roof can retain more rainfall BY: DON MOSELEY than previously found by most studies of smaller roofs. Up to 3.5" were detained during some rainfall events. The soil layer on the roof is only 4" deep, roof was the largest, most inTHE COST-BENEFIT tensively monitored green roof with 3" of media over a 1-inch ANALYSIS foam-type drainage mat. No Walmart has completed a study in the world. Each side was ponding or drain clogging on instrumented with equipment of the performance of green to measure variables impacting the green side was observed. roofs in collaboration with store energy use and stormwa- Of the 100 precipitation events Arup, Roofmeadow, Pennter runoff dynamics. Monitor- that were studied, the green sylvania State University, the roof retained an average of ing ran for three years. Data Green Team and University analysis included incorporation 74% (80-90% of small storms of Toronto researchers. This and 60% of the largest storms). of field results into detailed work centered on a research Peak runoff from the green models. roof built in 2006 at Walmart roof was delayed 1.25 - 3.25 store #5402 in Chicago. The hours from the rainfall peak, 133,000 square foot roof is just Energy and the rate was 50% to 85% over half green (vegetated) and The green roof saved energy lower than the precipitation compared to the white roof. If just under half white (cool) peak rate (average 65%). a full store had a green roof, roof. When constructed, this LIVING ARCHITECTURE MONITOR / SPRING 2014 / 24 Maintenance and Roof Life The Walmart Chicago green roof costs roughly 45% less to maintain than a typical white Walmart roof. This is due primarily to the protection the green roof affords the membrane and drains, preventing damage and clogging. Minimal selective weeding and avoidance of irrigation at this location helps to keep green roof maintenance costs low. Green roofs also can be expected to extend the life of the waterproof membrane from a typical 15 years (as low as 10 or as high as 25) to 40 or more years. The Bottom Line A financial analysis was done for green vs. white roofs in 9 locations (6 metro areas). The approach to this financial analysis differed from a typical one, in that it compared not just the two roofing systems in isolation, but a development package that includes a green roof with one that uses more conventional means to comply with relevant regulations. The results showed green roofs have a less than 20 year payback for all locations studied. One third of the total show a 0-3 year payback. Of the locations studied, Portland had the highest potential green roof net present value (NPV) for variables considered, and the only first cost savings potential, even excluding the direct incentive. This study demonstrates that in the right policy environment, green roofs can be an attractive voluntary choice for a retail developer like Walmart. THE ONE-ON-ONE WHY DID WALMART DECIDE TO IMPLEMENT GREEN ROOFS ON SOME OF THEIR STORES? HOW DID WALMART JUSTIFY THE READ THIS ISSUE ONLINE AT WWW.LIVINGARCHITECTUREMONITOR.COM http://WWW.LIVINGARCHITECTUREMONITOR.COM

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2014

Green Roofs - Living Architecture Monitor - Spring 2014
Contents
From the Founder
On the Roof With...
Policy and Standards
Research
Gap Leadership
Confessions of a Green 'Starchitect'
Sprucing Up
Green Roofs and Walls in Music City
Space in Transition
Big Box Retailers Embracing Green Roofs?
Exploring England's Green Roof and Wall Industry
New GRHC Corporate Members
GRHC Buyers Guide
Professional Calendar
Dirty Thoughts

Green Roofs - Living Architecture Monitor - Spring 2014