Shade Planning for Schools

47 Shade Planning for America’s Schools Chapter 6 Describing a Tree’s Canopy Density The task of describing a tree’s canopy density is somewhat subjective since there is no common metric. For the purposes of shade planning one could describe the density of a tree’s canopy by rating it as “open,” “moderate,” or “dense.” Standing beneath the tree and looking through its branches, if over 90% of the sky is blocked by the tree’s canopy, it can be described as “dense.” If between 50% and 90% of the sky is blocked by the canopy, it can be described as “moderate,” and if less than 50% of the sky is blocked by the canopy, it can be described as “open.” An open canopy provides little UV radiation protection. Measuring Existing Shade The final task of the shade audit is to estimate the amount of existing shade on the school grounds. Measurements should be taken of all shade, regardless of whether it is off-limits. There are two methods for measuring shade, one of which is highly technical and requires a working knowledge of both solar geometry and computer-assisted design software. The second method requires only that the planning team mark the shade patterns on the ground at the times of day that the school grounds are used. The ground can be marked with chalk, rope, or baking flour, then measured and marked to scale on the site plan. Measurements at several times during the day and throughout the school year will be neccesary to ensure that adequate shade is provided at the right time of day, throughout the year. If the sky can be seen by those under a tree or structure, they are at risk for exposure to indirect UV radiation. Considering Potential Shade Strategies Having collected information regarding the activity patterns of the different users of the school grounds and the shade patterns cast by trees and buildings, it is now time for the planning team to assess their findings and make recommendations to the school community. The planning team might find that the school grounds provide adequate protection from both direct and indirect UV radiation; however, if not, the team will need to make recommendations for making more shade accessible to students, teachers, staff, and visitors. The team should first consider strategies that increase the amount of accessible shade at very low or no additional cost to the school. These might include revising school policies to allow access to off-limits shaded areas or relocating playground equipment or picnic tables to areas of the school grounds where shade already exists. The planning team will also need to consider reflected UV radiation in their recommendations. These may include modifying ground and building surfaces to reduce their reflectivity. The planning team might determine that climbing vines would be the best solution for the indirect UV radiation reflected off a smooth wall or that artificial turf would be most appropriate to reduce the UV radiation reflected from a concrete playground. The team should engage in a process to help them examine the cost effectiveness of strategies that could be employed as they are evaluating whether or not a particular strategy will accomplish the intended goal. More information about this is provided below. The Shade Planning Matrix The Shade Planning Matrix is a tool that can assist the planning team with comparing potential strategies for achieving their goals while examining and comparing the cost