Green Roofs - Living Architecture Monitor - Spring 2012 - (Page 20)

INDUSTRY RESEARCH SIzE MATTERS A TESTING LAb PROVIDES INSIGHTS ON GROwING MEDIA by SAM fERRO T esting labs have a somewhat unique view of the green roof industry. Experience from testing of the many diverse products that come to our lab provides insight into how different components can affect the performance of growing media. Most green roof growing media mixes are comprised of a combination of lightweight aggregate, soil (usually sand), and organic matter (usually compost). Whether a twopart, three-part, or multi-component mix, it is the type of base materials used and the ratio at which the base materials are blended that gives the mix its unique properties. The size of the actual components used for green roof growing media and drainage aggregate has a profound affect on the performance. While it may seem obvious that particle size affects performance, the extent to which size affects performance may not be so apparent. Changes in component size can have just as big of an affect on the growing media as changes to mix ratios. Lightweight aggregates, such as expanded shale, clay and slate are the most widely used aggregates in green roof growing media. Other lightweight aggregates, such as pumice, lava rock and calcined clay are also used. Lightweight aggregates are used because they provide cation exchange capacity, and have pore space for air, water, nutrients and microbes. The size of the particles affects the drainage rate (permeability) and to a lesser extent, water retention and release to plant roots. Larger particles provide for faster drainage and less water retention. The size of the pores in the aggregate also affects the amount of water retention, absorption and water release. The larger the pores the more space for water and air, the smaller the pores the greater the absorption. If weight is a factor, material that absorbs the most water will also increase the weight of the media by the weight of the water. Most lightweight aggregates range in size from one millimeter (mm) to 12.5 mm. Particles larger than 16 mm are usually not recommended for growing media. Small changes in the amount of lightweight aggregate can cause big changes in growing media properties. In some cases, a change in the ratio of lightweight aggregate is the single biggest factor in the overall performance of the mix. Since lightweight aggregates are the largest component in most mixes, small changes in their content have a major affect on the structure of the mix. Coarser mixes have lower water retention, http://www.sempergreen.com http://www.sempergreen.com

Table of Contents for the Digital Edition of Green Roofs - Living Architecture Monitor - Spring 2012

Green Roofs - Living Architecture Monitor - Spring 2012
Contents
From the Founder
Seen & Heard
Bookshelf
Special Thanks
On the Roof With…
Innovation
Urban Agriculture Summit in Toronto August 15th – 18th
Citiesalive in Chicago Oct 17th – 19th
Policy and Standards
We Asked Experts Their Opinions on Modular or Loose Laid Green Roof Systems, Check Out What They Said
I Guess Size Really Does Matter! — Growing Media Insights
Eleanor Mckinney Taking Austin by the Horns
New Industry Products
Green Roof Falls Flat in New York City
Green Roofing Leader Shows Industry What They’re Made Of! Tremco Incorporated
Plant Profile
New GRP’s
Professional Calendar
New Corporate Members
GRHC Buyers Guide
On Spec

Green Roofs - Living Architecture Monitor - Spring 2012