A. Robert Randall responds: Not much. Plywood used in a built-up header adds little to the strength of the beam (see "Sizing Built-Up Wood Headers," 4/92). At best, if the plywood extends the length of the header in one piece, it only adds about 8% to the beams load-bearing capacity.
Construction adhesive, such as PL, adds nothing to the strength of a beam when the loads are vertical. In some cases, when significant lateral, or sideways, loads are anticipated, adhesives might be part of an engineer’s design. However, since conditions on site make it difficult to control dirt, moisture, temperature, and other factors that...
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