A New Slant On Shading

摘要

Variations of fixed shading of windows have been devised over time. Early examples, perhaps by accident or structural constraint, have the lower extremity of the eaves extension beyond the wall line at some nominal height above the window head. Also, in the case of gable roofs, the eaves extension has been carried across the gable end, providing the same all round shading achieved with a hip roof. In this era of "passive solar design", various bodies and researchers have proposed procedures for the proportioning of eaves width, with or without height above window head, relative to window height taken into account. No standardised requirement has, however, been established but the consequential performance is taken into account by energy efficiency rating programs. A de facto standard has been established by the typical detailing of roof truss manufacturers, with horizontal eaves soffit aligned with the window head. Gable end eaves have effectively disappeared. Typical eaves, as an extension of a water shedding surface, are not the ideal model for fixed devices for discriminating between admitting or obstructing solar radiation on a seasonal basis. An alternative approach with the eaves "soffit" and pergola frame rising away from the face of the wall is proposed and the benefits to passive heating are discussed.