Load Paths

All loads start at the roof and transfer vertically through the building to the foundation. If theses loads are not transferred properly, it can result in the cracking of interior finishes, sagging framing or crushed joists.   Building inspectors pay close attention to broken load paths and will red tag a job when they are encountered in a structure. Problems in transferring loads can be avoided by aligning load bearing walls over supporting beams or walls, proper placement of roof framing and corresponding support struts and transferring column loads directly to the foundation.   Loads carried by bearing walls or posts must be transferred through the floor system. If a bearing wall does not line up with a bearing wall, post or beam below, the floor joists in between can be overstressed and cause severe deflection.   Load bearing walls can be offset from supports below, but only by a distance equal to the depth of the joists. For engineered wood I-joists, the codes require the loads to line up directly over each other and solid blocking or vertical squash-blocks are required to transfer the load around the web of the wood I-joist. Specific engineered designs of either solid-sawn lumber or I-joists may allow placement of loads at other locations, but discontinuous load paths should not be attempted without consulting an engineer. Struts are often used to support roof rafters when their lengths exceed the recommended clear spans.   These struts should be supported by load bearing partitions or braced to a purlin running across the rafters and should form an angle not less than 45 degrees. Rafter struts should not land on non-load bearing walls or rest on "strong backs," the 2x bracing that runs across ceiling joists.   Columns must bear on elements that can support them. Resting a column on a floor or rim joist without extra blocking or support underneath can crush the underlying joists.   All columns should run continuously to the foundation. If that is not possible, the column should be supported by a beam or header designed to transfer the load to other columns or bearing members. To support a column on a rim joist, add full-depth vertical blocking inside the rim joist to the full depth and width of the column base. Load