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Planting trees in suburban office parks and corporate campuses is a proven strategy to increase the attractiveness of and provide cooling shade to projects. Unfortunately, there can also be a negative impact of tree planting which is the damage that often occurs when tree roots and infrastructure, such as sidewalks and curbs, interact. A recent survey of 18 California cites revealed that approximately $70.7 million was spent annually statewide due to root and hardscape conflicts. The single largest expenditure was for sidewalk repair ($23 million), followed by curb and gutter repair ($11.8 million), and trip and fall payments and legal staff time ($10.1 million). These costs reflect only public figures and do not include the considerable private costs associated with root and hardscape conflicts. In 1976, DeepRoot introduced the first commercial root barrier, a practical and economical method to prevent damage to hardscapes from roots. DeepRoot barriers have been a successful and common product throughout the San Jose region for years and a recent installation in 1999 at the Alza Corporation headquarters in Mountain View (just north of San Jose) is an excellent example of the current design standard using DeepRoot tree root barriers. There are two primary planting methods with root barriers, commonly known as linear and surround. Studies have proven that increased soil volume leads to improved tree health. As a result, the linear planting method, where the barrier is placed directly along the side of the hardscape needing protection, has become more and more common. The barriers deflect the roots downwards, away from the surface rooting that causes most damage. By employing the linear planting style the tree is given increased soil volume while the hardscape receives the protection it needs. In the alternate method of surround planting, the barriers surround the root ball, leaving a minimum of 4"-6" of soil between the edge of the root ball and the barrier. This planting style is used when the tree is surrounded on all four sides by hardscape. The Alza Corporation headquarters is a prime example of the new wave of design that incorporates greater soil volume for trees while minimizing the potential damage and costs to hardscapes by using root barriers in a linear planting style. In this project, completed in 1999, 24" depth root barriers line both the sidewalk and the curb while the trees have access to ample soil volume. Three years later, the sidewalk, curb and gutter remain perfectly intact while the trees will have the best opportunity to grow into large mature specimens that provide cooling shade and add beauty to the corporate campus. Root barriers work by taking advantage of the natural growth habits of roots. Roots are opportunistic and will grow wherever adequate conditions, including oxygen, water and other nutrients, exist. As a root grows out from the root ball, it comes in contact with the barrier. Since the root is unable to penetrate through the barrier, the root turns and follows the wall of the barrier until it hits one of the molded vertical ribs that are part of the barrier design. These vertical ribs direct the tree roots down and out the bottom of the root barrier where it continues to grow away from the planting pit without causing any damage to hardscapes or utilities. The Alza project provides an excellent example of one of the key points when installing a root barrier, which is to keep the top edge slightly above grade (typically _ - 1 inch). In this case, the barrier is just visible above the finish grade. This is a critical part of the installation sequence because if the top edge is buried, roots growing laterally will grow over the top without coming into contact with the barrier, thus defeating the purpose of the barrier. Other key elements to look for when specifying a root barrier are the following: o Integral 90? vertical ribs to redirect root growth o Ground lock pads to ensure the barrier is not lifted by roots growing underneath the bottom of the barrier o An integrated joining system for easy installation o A double tope edge that provides strength and stability for the above ground portion of the barrier An important distinction must also be made between the use of a root barrier and a root block. A root block is used when it is not desirable to redirect growth downward, but roots must be prevented from entering a certain area. The primary difference between a root barrier and a root block is the absence of a vertical rib to redirect growth downward. With a root block, the roots will generally turn along the smooth barrier and stay on the same horizontal plane. Caution must be used to ensure the root block is placed beyond the structural root zone to prevent wind throw hazards. Examples of typical applications are home foundations with clay soils (roots grow under the foundation into the clay, withdrawing the moisture and disrupting the soil equilibrium), bike paths and other long linear applications. In the case of the Alza project, the use of a deflecting barrier was appropriate given the need to ensure adequate anchorage. It is important to realize that tree root barriers are not a cure-all. Any good planting plan will include room for the tree to mature and develop, and include adequate drainage, soil volume and nutrition. It is recommended to prepare a healthy environment for future root growth in the soil below and surrounding planting area. Whether planting with or without a barrier, the need for proper planting practices cannot be over-emphasized. The Alza project is an excellent example of a planting site that has taken the long-term health of the trees into account, successfully incorporating proven technology to prevent damage. This combination will enable the trees and the hardscape to peacefully co-exist for many years to come. When it comes to safety surfacing, there are a lot of companies out there and just as many options to choose from. Keep in mind this isn\'t everything, so I guess you could say we're "just scratching the surface." hello

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November 22, 2019, 1:47 am PDT

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