DEAR TIM: This is the year of the deck at my home. I’ve scheduled the time off and I’m ready to build. However, I need your help on several things. How do I connect the deck posts to the deck? How do the posts connect to the concrete pier, or do they just rest on the concrete? Should the posts be buried in the soil? How do you calculate where to place the concrete piers so the posts are centered on them? Can you just come over and help me do all this? – Catherine R., Uncasville, Conn.
DEAR CATHERINE: I’m hoping your deck is a small one and not too high off the ground. That’s a good beginner’s project, especially if the deck is just one level and a rectangle or a square.
As the deck industry has exploded, manufacturers responded by developing engineered metal connectors that allowed carpenters and homeowners to safely and securely connect the parts of decks so they don’t fall down. Deck collapses are a real concern, people get killed or severely injured when decks suddenly fall to the ground.
You’re going to use approved galvanized metal connectors sized to your deck lumber to connect the vertical posts to the outer beam that supports your deck joists. The most common connector is a plate that has two tabs of metal that point up and two that point down, creating shapes of the letter U. Special corrosion-proof fasteners are used to connect this metal bracket to the post and beam.
As for joining deck posts to the concrete piers, you should use similar metal connectors. There are several types of metal post bases, but they all connect to the concrete pier and to the wood post.
You don’t want the deck posts to just rest on the concrete pier. Wind uplift, shifting soil, garden tractor accidents, etc. could cause the post to shift off the pier, which could contribute to the deck collapsing. Connecting the post to the concrete pier anchors the deck to the earth.
It’s not a great idea to bury the deck posts in the soil. I’ve seen lumber that’s treated for ground contact succumb to rot and insect infestation. Keeping the treated lumber above grade allows it to dry rapidly, extending its useful lifespan.
The placement of the concrete piers that support your deck posts is critical. I learned long ago from a fellow carpenter a fairly easy way to place them perfect each time.
I’ve found it best to create the actual outline of the deck using the deck lumber. This means you’ll connect the ledger board to your home using all the approved flashings and internal metal connectors ensuring this board will not pull away from your home.
You then attach the two end joists that extend out from the house and cap those with the band board joist that runs parallel with the ledger board along the house. You now have a square or rectangular box. Suspend this box in the air with temporary posts made from 2-by-4s or 2-by-6s. Make sure the box is level and square.
You can now suspend an old-fashioned and reliable plumb bob from each corner of the box to the ground. These two points on the ground can be used to help you calculate the exact position of your concrete piers based on the deck plan you’re using.