Planning Key Ingredient in Deck-Building

DEAR TIM: I will be building a deck soon, and need some tips. What is the best way to connect a wood beam to the wood deck posts? Doug F., Harleysville, Pa.

DEAR DOUG: I am not certain there is a best way. My guess is you could put several structural engineers, a few seasoned architects and some crusty deck-building carpenters in a room and come up with a wide variety of "best" solutions. I can tell you several of the methods I have used over the years that have worked really well for me, and I will gladly share with you a method I would avoid at all costs.

When I go to friends' houses and open houses I am often shocked to see how do-it-yourselfers and even paid contractors attach deck beams to wooden posts. What astonishes me is the lack of forethought into the amount of weight that is supported by two simple deck posts. Anyone who has lifted a single 2-by-12 treated-lumber floor joist knows that the cumulative weight of a deck can easily be in the thousands of pounds. Then imagine what happens when you have a large party and people are shoulder-to-shoulder on the deck.

The bottom line is that you can have multiple tons of weight constantly trying to fall to the ground under the influence of gravity.

The beam you are working with often supports half or more of the weight of the deck, plus anything that sits on the deck. The floors joists, decking, furniture and people rest on the beam, and transfer the load to this beam along its entire length.

Frequently I see people who have taken a beam or two joists and simply nailed or bolted these parts to the sides of the post. The entire weight of the deck is borne by four or more simple bolts or nails. These fasteners may not be designed to handle the weight. If the lumber dries and shrinks, this connection can become significantly compromised.

I prefer to have deck beams rest directly on a shelf or notch in a slightly oversized wooden deck post. This notch is easy to create with a standard circular saw and a traditional handsaw. Many decks' beams are made up of two 2-by-12 deck joists that can carry the design load. The joists don't have to be placed immediately next to each other to support the load of the deck. They can be spaced several inches apart with an air space that helps prevent rot.

I have created this connection in the past by using a 6-by-6 wooden deck post. These posts normally measure 5 inches square. The thickness of the two floor joists is a little over 3 inches, so when you create two notches on opposite sides of the post, you are still left with a beefy 2 inches of post material. This remaining tongue of wood extends to the top of the beam.

The two parts of the beam are through-bolted to the wood post to make a strong and permanent connection. The entire weight of the deck rests on the bottom of the notches in the post instead of hanging precariously on four or more bolts.

You can also buy code-approved metal brackets that allow you to connect wood deck beams to wooden posts.

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