Masonry openings in buildings are frequently not exact and are referred to as rough openings for that reason. When window products are placed into openings, they often need to be shimmed into place to properly fit the opening. When a large amount of shimming is required, 1x or 2x pieces of wood are utilized and are referred to as bucks.
Product evaluations issued by accredited entities specify how to fasten window products to host substrate with a maximum shim thickness. However, if the window is only fastened to the buck, then the buck needs to be securely fastened to the host structure. According to section 1710.10 of the 2014 Florida Building Code (5th Edition) (similar for the IBC code), “where the wood buck thickness is 1 ½ inches (38 mm) or greater, the buck shall be securely fastened to transfer load to the masonry, concrete or other structural substrate…”.
From an engineering standpoint, securely fastened is entirely open to interpretation and has us constantly asking ourselves, what the buck?
Topic credit: Zach Rubin, EI
Mar 11, 2016 8190 Engineering Principles
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