14A — April 27 - May 10, 2012 — Green Buildings — Mid Atlantic Real Estate Journal


G reen B uildings F eaturing E nergy E fficiency By Stephen L. Johns, VanDemark & Lynch, Inc. Should you be considering a green roof? (No - you won’t need a John Deere tractor) B eing green often means combining old technolo- gies with newmaterials.

plants, typically a sedum, that require minimal maintenance. The sedum is usually planted in a four-inch layer of a special lightweight soil mixture placed over a drainage fabric, which covers a single membrane roof- ing fabric. Deeper soil can be used if a more diverse vegeta- tive cover is desired for use as a rooftop garden. The question that needs to be answered is whether you will benefit from a green roof. Green roofs have five primary beneficial impacts: First , green roofs extend the life of the roof. The plant mate- rial and soil insulate the roofing membrane from the sun. This

eliminates the extreme peak temperatures experienced by the roof, and the deterioration of the membrane from ultra- violet solar rays. The accepted standard is a green roof will last over 50 years. There are green roofs in Europe that are well over 50 years old and still in excellent shape. Second , green roofs reduce air conditioning loads. The same insulating features that extend the life of the roofing membrane, also reduce the heat transferred through the roof to the building. This benefit is more noticeable in a single story building, since the benefit is not realized by the lower floors in a multi-floor

building. Unfortunately, the insulating effects of the green roof are not as effective for heat- ing loads. Although it does not make the building any colder, having a block of frozen soil on the roof does not keep the build- ing warmer. So, the benefit of reduced utility costs is generally limited to cooling loads. Third , green roofs manage storm water, and will signif- icantly reduce the need for other storm water manage- ment (SWM) facilities around or near the building. The most important SWM benefit green roofs provide is management of stormwater quality. Green roofs typically clean and reduce

the temperature of stormwater sufficiently to satisfy most regu- latory agencies. Green roofs also reduce the rate and volume of runoff, so they can also reduce the need for quantity control SWM facilities. Increasing the depth of the soil will increase the benefits of stormwater quan- tity management. Sometimes replacing existing roofs can add to this benefit. VanDemark & Lynch, Inc. helped one property owner install a green roof on an existing building, and docu- mented it with the regulatory agency, so it is now “banked” to count as SWM for a future facility expansion. Four , green roofs reduce sound intrusion. The green roof ’s soil bed is an excellent sound insulation. This is ex- tremely helpful for buildings near airports, or for theaters and concert halls, or other fa- cilities where outside noise is a nuisance. Five , green roofs provide a message to the community that the owner is interested in be- ing a good steward of natural resources. A green roof can be used in a number of ways to brand and market a facility. For example, it can be used in advertisements, or tours can be given to interested customers and community groups. To summarize, green roofs have a number of benefits. Fi- nancially, the best installation would be a one story, refriger- ated warehouse in the south, where the full impact of the reduced cooling loads would be experienced, or a concert hall within the flight path of a nearby airport, where the sound reduction is critical. But, green roofs have been success- fully installed on a number of institutional, commercial, and residential buildings in the north, away from airports. So, it certainly makes sense to do a cost/benefit analysis for any building, or even for a replace- ment roof, because the SWM effects can sometimes make a green roof the best option. Stephen L. Johns, PE, PLS, started working as a civil engineer, planner, and sur- veyor after graduation from the University of Virginia in 1976. As vice president of engineering, Johns’ current duties include managing the staff of VanDemark and Lynch and assuming the du- ties of Principal-in-Charge to lead the design process for significant projects. n

Green roofs h a v e b e e n used around the world for c e n t u r i e s . We have all seen the pho- tos of goats mun c h i ng the grass on

Stephen L. Johns

a roof. But in today’s world of green technologies, green roofs have evolved well past the need for livestock. Modern design concepts take advan- tage of the drought and flood resistant traits of succulent

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