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4 Copyright ©2013 Sefaira Ltd. F O U R RU L E S O F TH U M B TH AT CO U L D L E A D YO U A S TR AY What's Happening? The reasons for these failures is that the right balance between heating and cooling — and therefore the right amount of solar exposure — varies depending upon the specific design of the building. For buildings with self-shading or obstructions, finding this balance can become complex, because the majority of sunlight is not necessarily coming from the south. Rule 2: Shading Depth The Rule There are numerous rules of thumb for sizing shading devices. They typically follow this form: shading should be 1/4 the height of the opening in southern latitudes (36°L) and 1/2 the height of the opening in northern latitudes (44°L). The intent is to block sunlight in the summer months, but allow solar gain in the winter, when the heat is beneficial. When it Works This rule works well for externally-loaded building types (e.g., residential design), buildings oriented due south, and buildings whose envelope is built to "typical" specifications — meaning average levels of insulation, air tightness, etc. Our example building is a multi-family residence in London. Parametric analysis revealed an optimal shading length of 0.8 meters (2.6 ft.), which is in line with the rule of thumb. WHEN IT WORKS Standard envelope construc- tion (optimal shading is expected depth) WHEN IT MISSES High-performance construc- tion (optimal shading length is longer than rule of thumb suggests) Shading - Low Insulation Shading - High Insulation Shading - Low Insulation Shading - High Insulation Shading - Low Insulation Shading - High Insulation Shading - Low Insulation Shading - High Insulation

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