The Basics of Building a Deck

Built right, a deck can be an outdoor space that lasts for decades. Here's what you need to know before you get started.

| May/June 1989

I was crouched beneath the underpinning of the east deck, staring at a fungus that had, in four short years, firmly entrenched itself along the center of the ledger beam lag-screwed to the house. The point of my pocketknife confirmed what I'd suspected: The treated beam, despite its appearance, was essentially sound. Too bad I couldn't say the same for the structure's band joist. Where I could get the thin blade behind the warped ledger, the 2×8 rim was soft and pecky—leaving little reason to believe that the rest of the board wasn't damaged as well.

After duck-walking the 10 feet or so to daylight, I looked over the house site. A stand of old-growth evergreens on a slope that leveled out at the deck's edge. No gutter on the roof fascia above. Moving over to the railing and dropping an old Buick ball bearing onto the top of the platform, I watched as the steel ball rolled a lazy line toward the side of the house.

A Poorly Planned Deck Installation

What I'd discovered, of course, was something that occurs all the time—a poorly planned deck installation. Oversights aren't premeditated, so I suppose the real "crime" is that it wouldn't have cost much more to do the job right the first time—certainly far less than it would to do it again.

In this case, the evidence was plain: The beam connecting the deck to the house was installed without metal flashing, which would have directed water away from untreated wooden members. Haphazardly spaced lag screws were on the verge of losing their grip in several spots. An eastern exposure, shaded by trees for a good part of each misty morning, encouraged condensation. And finally—the kiss of death—the unguttered roof worked hand in hand with a deck pitch that sent water toward, rather than away from, the house wall.

Start with the Building Code Handbook

Imagine a deck as being the floor of a house without the walls attached. The structure must be able to support its own weight plus that of people and any furniture. That means the support posts should be sized and mounted properly, the beams set in the right places and the joists sized and spaced according to load. That, in a word, means planning.

A great place to start is with your local residential building code handbook. I paid $2 for our newest state-published text, which includes 134 pages of explanation, amendments and detail drawings. Individual counties may adopt specific requirements, but, broadly speaking, the code book offers two things in one neat package: the regulations (so you won't be in violation because of some neglected detail, even if you intentionally overbuild the structure) and some clear illustrations of various building techniques (which clarify, in many cases, what's being described).

Gary Birtles
3/6/2015 9:33:55 AM

I helped my dad build a deck he designed a few years ago. We made the mistake of not reading the code requirements before we started though. We had to alter our plans in order to keep up with code. Next time I'll remember not to make that mistake.

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