The Complete Handbook of Post Base Plates

Chapter 1: Understanding Post Base Plates

The post base plate is the unglamorous but absolutely critical piece of hardware that connects a vertical structural member—a post, column, or pole—to a horizontal foundation such as a concrete slab, a footing, or a structural frame. It is the load-bearing interface between the two parts of a structure that must not move. This connection is where structural failure can start, and it is the one area of a building that is most susceptible to rotting, corrosion, and code violations.

At its most basic, a post base plate is a flat steel plate with a central section that either holds the bottom of the post or sits under it, and it has holes in the flat section for anchoring to the base material. But that description undersells its job. The plate is a load transfer mechanism. It takes the full weight of the structure above—dead load, live load, snow load, wind load—and spreads it onto a larger footprint of the foundation. The larger contact area prevents the post from punching through the concrete or crushing the material beneath it.

Consider a classic example: a 4x4 post for a residential deck. If you rest that 3.5-inch-square post directly onto a concrete pier, the entire weight of that section of your deck is concentrated on about 21 square inches. If that pier has a rough, uneven top, the pressure point is on a couple of small bumps. That pressure, over time, will start to crush the