Expert advice on how to build a long-lasting deck

These creations by Lawrence Winterburn, of GardenStructure.com, combine art with long-lasting craftsmanship.

If you've got plans to build a deck this season, I've got some good news and some bad news for you. The good news is that decks are great. They add another dimension to your lifestyle. They're fun. They boost property value. But you probably knew that already. The bad news is something you've likely never heard before: good decks are rare. Really good decks that is. Sure, anyone can slap together a few 2x6s and call it a deck, but what about eye appeal? What about how it's going to look in 20 years? Beauty and durability are what separates good decks from bad, and it's these two things that you're going to learn about here.

Lawrence Winterburn is the guy with the know-how. He's a professional carpenter with 10 years experience designing and building all kinds of outdoor structures. His work has appeared in magazines like Canadian Living, Canadian House and Home, Canadian Home Workshop and Canadian Gardening. He's also a detail fanatic, and that's good. He regularly judges deck contests and is the founder and chief designer for www.gardenstructure.com, an online retailer of outdoor structure. Winterburn is the Felix Unger of deck design and construction.

The Vision

"Every good deck starts with a wish list", explains Winterburn. "What will you do on the deck? How many people does it need to accomodate? What features do you want? How much dough can you spend on the project? Next, make a scale drawing of the footprint of the deck on graph paper. It doesn't have to be perfect. One square to the foot is a good scale. You may also find a sketch of the house useful, or a large photo of the deck area of the house."

Building Forever

"The most common deck flaw is poor footings", warns Winterburn, "and to avoid trouble you need understanding." Deck blocks are factory-formed concrete feet, popular because they require no digging. But they're also risky. They usually work on undisturbed ground, though not on areas that have been back-filled. They're also free to rise and fall with the effects of frost. That's why you should never use deck blocks under structures that are also connected to a house foundation. If you've got to use them, put a round patio stone underneath each one, for additional stability.

Concrete pier foundations that extend below the frost line are among the strongest, most frost-proof and longest-lasting deck supports you can use. Unfortunately, concrete absorbs large amounts of ground moisture, and though the water doesn't affect the structural integrity of the concrete, it's a potent post rotter. So instead of sinking posts into concrete piers, keep them high and dry with galvanized post saddles, which you sink into the above-ground part of the concrete pier while it's still soft. An added advantage of this method is that if the posts do finally rot, you'll have some hope of being able to jack the deck up a few inches, clear away the rotted material, and install a brand-new support post.

Rot-Proof By Design

There's more to building a durable deck than choosing rot-resistant pressure-treated or cedar lumber to put on top of a solid foundation. Even the best deck will compost unless you design it properly. And that means keeping water drainage in mind. "The finest wood is wasted if you put it together wrong", cautions Winterburn.

It all boils down to the fact that wood is microbe food. But the critters can only sit down to dine when moisture content is high and temperatures are at least relatively warm. And although top-side deck surfaces do dry quickly after a rain, those parts of a deck frame in contact with each other don't. And that's the main weak spot you need to address as you plan your deck. Wherever wood comes in contact with wood or concrete in outdoor structures, you've got the potential - no, the likelihood - for rot.

The main problem areas are places where planks get spiked together to make built-up loadbearing beams. You'll also find it happening where deck boards meet end-to-end. The trick is to make sure that all parts of your deck can dry quickly between rains by minimizing contact areas, and by building those contact areas so they're small, ventilated and maintainable.

Shop-cut ventilation spacers made of 1/2-inch thick pressure-treated plywood are the first things you need to consider for your deck. They minimize moisture retention by separating wooden parts that would normally come in full contact with each other. On a built-up beam, for instance, slip them between beam planks every 18 to 24 inches as it's assembled. If you want to be really thorough, apply a bead of polyurethane caulking around both sides of each spacer before assembling the beam and using galvanized carriage bolts - not nails - to hold everything together.

You'll also find spacers appropriate as part of the deck-to-house connection. Most decks are bolted to the side of a house, rather than installed completely freestanding. This makes use of the existing house foundation, but it also causes a problem. Deck-to-house connections can cause a moisture trap that leads to rot, either of the deck header, the house, or both. Every deck situation is unique, of course, but some variation of the plywood spacer idea should be included in all deck-to-house connections. Also, never underestimate the ability of water to penetrate tiny cracks. That's why you should always apply polyurethane caulking in and around the hole where an anchor bolt penetrates the house.

The end grain of a board is its most vulnerable spot, because the cellular tubes that were part of the tree's feeding structure are open there and still able to suck up moisture to an extent. And adjacent end grain areas that touch each other spell double-trouble because of their moisture-trapping interaction. That's why you should consider spacing the ends of deck boards 1/4-inch apart, so wherever two deck boards would normally butt together there's a ventilation space that lets wood dry quickly.

Since a single joist is too narrow to allow deck boards to be pulled far enough apart for end-to-end venting, consider double joists wherever deck boards will end. Plan your framing carefully and you'll only need a double joist every 4 to 6 feet. Sounds like a waste of wood? Not really. You'll be fully repaid for the slight extra cost by the longer life of your deck surface. Another double-joist plus is that you can drive screws further away from the ends of each deck board, minimizing splitting that often happens at board-ends.

Want to boost the eye-appeal of your deck and make it easier to finish well? A small hand-held router with a 45-degree chamfering bit does a great job dressing up otherwise-ordinary deck boards. After trimming each one to length, run around the outside with the router before fastening it. The eased edge not only looks great, but is easier to finish than square-edge deck boards.

Structural Deck Maintenance

Despite spacers, caulking and care to minimize wood-to-wood contact areas during construction, there are still places where ventilation between deck parts is poor and rot will be promoted because of retained moisture. Wherever main beams rest on support piers, for instance, or support beams meet with vertical posts, you'll find rot-prone danger zones. And here's an approach to keeping these places sound and solid indefinitely.

As you build, create ports, valleys or troughs where you can pump in a shot or two of liquid wood preservative every couple of years, during dry times of the year. Using a portable pump-up weed sprayer it takes less than an hour to do a very large deck. A small price to pay for an operation that virtually eliminates the chance of rot in vulnerable areas. Clear, zinc-based preservatives work best for this since they dry invisibly. Wear safety goggles during application, and mark the weed sprayer for this exclusive use.

Replaceable Rot Plates

An alternative to aiming for total rot prevention is to accept that some rot is eventually inevitable, and that you'll have to replace certain parts of your deck at some time. To make that replacement job easier, create removable wooden rot plates in key areas such as under joists or beams where they rest on support piers, or where the deck rests on part of the house foundation. Rot plate is just a fancy name for a piece of pressure-treated 2 x 4 or 2 x 6 lumber, sandwiched between a main deck component and the concrete pillars the deck rests on. A rot plate can be screwed in place, or held by the weight of the deck. To replace one, just loosen screws or bolts, then jack the deck up slightly to pull out the old rot plate and slip in a new one.

Nails and Bolts

Nails, it turns out, can rot surprisingly quickly, especially when they're pounded into pressure-treated lumber. A 1980s study by the American Plywood Association compared the corrosion resistance of 31 metal fasteners under accelerated exposure conditions, and found that even so-called outdoor-quality electroplated nails were a poor choice for use in pressure-treated, outdoor wood. They're the very shiny-looking ones.

Hot-dipped galvanized nails are better, so long as their coating remains intact while hammering. They have a matte-grey coating and are often rough with blobs of zinc. The all-round champions in the APA study were stainless steel nails. No surprise there. Stainless is more expensive and harder to find than hot-dipped galvanized, but you should consider it for at least the important-but-inaccessible areas of your deck, areas you'd have trouble renailing after the fact.

Deck tips like these may seem like a silly waste of time to builders who just bang together airborne wooden rafts all day, the faster the better. And even if these slap-happy decks do last 15 or 20 years, is that really long enough when 20% extra time and attention spent during construction can yield 10, 20 or even 30 more years of life? Decks are expensive, both financially and environmentally. Doing a good job the first time is just another example of how quality invested up front more than pays for itself over the life of a structure.