A. The critical issue with built-up beams is that all the layers must deflect together and by the same distance in order to be properly sharing the load. For beams where the load comes down evenly on top of the beam, such as drop beams or beams directly under bearing walls, the nailing pattern is not all that critical. All you need are enough nails to hold the layers together and keep them from twisting. For beams loaded from the side, however, and especially for beams loaded from one side only, the nailing pattern is critical.

When beams are loaded from the side, there must be enough nails to transfer the load through the loaded member and into the attached members. For example, if a beam consists of three 2x10s loaded from one side only, the loaded member should only carry 1/3 of the weight. To transfer the rest of the load into the attached members there must be...

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