Rot Resistant (Built-Up) Deck Beams

July 10, 2015


Better beams can drain and dry

The typical way to build a deck beam is not the best way. Normally, two or three 2x8s or 2x10s are nailed together with 16d spikes, three or four every couple of feet.

This is a plenty strong way to build a beam, but it can trap moisture and crud (making moist crud) along the top where the 2x8s meet. Because the edges are rounded slightly, this joint creates a groove in the top of the beam, which traps water and remains damp for a long time after a rain. 

Damp beams = #BugsMoldRot.

The better way to build a beam is to use half-inch spacers between the layers. The space allows drainage and airflow. 

In this video, Steve Maxwell illustrates a good way to make the spacers: pressure-treated plywood with pointed tops to shed water. He recommends using carriage bolts, rather than nails, to draw the beam together.


Steve Maxwell is a home improvement contractor in Manitoulin Island, Ontario, Canada. Hiswebsite and YouTube page offer many  informative videos, articles, and photos.

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