b'Structural MullsH Mulls and Snap Mullsare Mechanical Mulls,designed to join two or morewindows where the windowsdo not need to be structuralor support any weight.Stacking two windows, oneon top of the other, wherethose windows can beanchored to the surround-ing rough framing is accept-able for most residentialapplications where windowpressures are not near hur-ricane or even tropical force.When windows (and doors)are joined in an area nearthe ocean or where highwinds can be expected, a structural mull is required to meet mostbuilding codes.A Structural Mull is usually a piece of steel with legs at top andbottom that allow the mull to be securely fastened to the headerand sill - or even to the jambs where a horizontal mull is required.Then the window units are anchored to the mull with high perfor-mance fasteners so that the finished assembly is a structural unit,secured to the surrounding framing and forming a weather andwind resistant fenestration unit.Where codes demand it, the structural mull is used in testing of the window and door units themselves in order ot get a rating which then is used to determine compliance with the required performance for the climate and region.When it is necessary to install window and door assemblies thisway, there are usually engineering drawings showing the propermull size and anchoring details of both the mull(s) and the windowor door units.Window Fitters Guide to Window Installation802020 AWDI, LLC Do not reproduce without permission'