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Weather Proofing a Deck

Though mankind has been erecting wooden buildings for millennial, 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″ x 4″ x 8′ 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 saw-logs 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 over cut. Most of us wouldn’t buy fresh redwood even if we 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 modem 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.

The latest plans and how-to books and videos incorporate rot- and pest-preventing measures learned over a half-century of practical experience. But, fair warning: the deck plans in the old how-to books you find in every library (and those still sold by some plan services) hark from the 40s, when decks were a novelty. Structure may be too weak to hold up or to satisfy building codes, and lumber/fastener specs will surely be out of date. Most importantly, the latest materials and techniques to guarantee long-term structural integrity and minimize water, rot, and insect damage will be missing entirely. If only to stay legal, be sure to have any construction plan pre-approved by your local building-permit authority. They will turn up serious structural deficiencies, but won’t mention the modern niceties that can add decades to your deck’s service life.

You will want to talk with your professional deck contractor about the latest weather preservation tactics for your new deck. Make sure any articles you read are current so you can receive information on the latest products available.

Matthew Millsap is a home improvement expert. He believes in consumer education. If you need more information or are looking for quality Weather Proofing a Deck please visit