47.5 MB - The Whole Building Design Guide

will depend on the gutter uplift load and strength of theconnections between the gutter/strap and the strap/wall.Note that FMG Data Sheet 1-49 recommends placing straps10 feet apart. However, at that spacing with wide gutters,fastener loads induced by uplift are quite high. When strapsare spaced at 10 feet, it can be difficult to achieve sufficientlystrong uplift connections.When designing a bracket’s lower connection to awall or a strap’s connection to a wall, designers shoulddetermine appropriate screw pull-out values. With thisoption, a minimum of two screws at each end of a strap isrecommended. At a wall, screws should be placed side byside, rather than vertically aligned, so the strap load is carriedequally by the two fasteners. When fasteners are verticallyaligned, most of the load is carried by the top fastener.Since the uplift load in the corners is much higher than the loadbetween the corners, enhanced attachment is needed in cornerareas regardless of the option chosen. ASCE 7 provides guidanceabout determining a corner area’s length.Parapet Base FlashingsInformation on loads for parapet base flashings was first introducedin the 2002 edition of ASCE 7. The loads on base flashingsare greater than the loads on the roof covering if the parapet’s exteriorside is air-permeable. When base flashing is fully adhered,it has sufficient wind resistance in most cases. However, when baseflashing is mechanically fastened, typical fastening patterns maybe inadequate, depending on design wind conditions (see Figure3-66). Therefore, it is imperative that the base flashing loads becalculated, and attachments be designed to accommodate theseloads. It is also important for designers to specify the attachmentspacing in parapet corner regions to differentiate them from theregions between corners.3-80 MAKING CRITICAL FACILITIES SAFE FROM High Wind