Building a Weatherproof Deck

Building a weatherproof deck that will withstand any climate or condition, including: deck posts, butt joints, dry rot, ledger, cutting, fastening and types of lumber.

| June/July 1996

Building a weatherproof deck that will stand up to any climate or condition. (See the deck building diagrams in the image gallery.)

Building a Weatherproof Deck

I learned how not to build a deck one day this spring when mine threatened to fall off the house. I didn't build that deck, understand. It came with the c.1970 mountainside cabin I retreat to now and again. But, to be honest, if I had built the deck by the standards of its day, the same problem might well have occurred.

Though mankind has been erecting wooden buildings for millennia, we seem to learn mainly through hard experience ... and open-to-the-weather, natural-finished wood decks are a comparatively new idea. They didn't begin to replace traditional roofed entry stoops and porches till the concept of an "outdoor room" became popular during the postwar housing boom of the late 1940s and early 50s.

Lacking a porch's roof and water-resistant painted finish, the wood of a deck is fully exposed to the elements. And it took a while for us to learn how to build and maintain a structure that has all of nature's processes allied against it—the wood alternatively soaked and dried, frozen and sun-baked, assaulted by forces of wind and snow, hail, and acid rain, plus, on muddy days, battering from your youngsters' Big Wheel. From nature's perspective, deck lumber is nothing but dead wood to be recycled into forest mold, and the mold into plant nutrients to fuel new growth. Woodpeckers, gnawing bugs, and mildews will attack it from the outside, termites and bark beetles and carpenter ants will bore in and tunnel through the inside, and whole legions of fungi, rot molds, and bacteria will infiltrate it. Together, they can convert a shiny new kiln-dried fir or spruce 2 inch by 4 inch by 8 foot stud to a heap of sawdust in a very few years.

Some woods, however, produce toxic oils that repel insects and kill mold spores and bacteria, serving as pest deterrents for the living tree, and in lumber acting as natural preservatives. Bald cypress, California redwood, the white and red cedars, and a few others will last ten, perhaps fifteen years till the oils degrade or wash out. But cypress has been in short supply for decades. A generation ago, California redwood was plentiful, shipped nationwide, and relatively cheap, so most decks used it. Today, of course, standing cypress is preserved from logging; what little cypress lumber is available comes from old abandoned sawlogs being dredged from river bottoms where they sank 100 years ago—and it sells at antique-furniture prices. As we all know, the once vast redwood forests are being overcut and I for one wouldn't buy fresh redwood even if I could afford it. Even eastern red and western white cedar has become so scarce of late that its price is as high as redwood.

With the cost of naturally decay/bug-resistant woods outtasight, most decks today are built of "PT"—common softwood lumber that's been "pressure treated" with rot-proofing chemicals. If overhauled periodically, pressure-washed frequently, and treated annually with the latest exterior wood preservatives and waterproofing compounds, the wood in a modern PT deck can hold up against weather, bugs, rots, and molds indefinitely. Modern fasteners and fittings—such as deck screws and the joist hangers used to join the deck frame and beams (joists) that hold the planking—are also made to last of hot-galvanized steel or rustproof alloys that won't "weep"—make those ugly dark streaks of corrosion you see streaming down the wood of so many decks and fences cobbled together with common nails or power-staples.

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