From The Correct Method
Q. I recently moved into a poorly maintained home that was built in the mid-’70s. It’s clearly time to replace the rotted-out deck, which was built with untreated, stained wood. My question: How do I properly attach the new deck to the house? The old deck’s ledger board was simply nailed onto the wall, and there’s ample evidence that water is finding its way into the basement framing and under the door onto the main floor. In fact, I’ve already replaced some spongy underlayment inside the house in front of the deck door. There must be correct methods of attaching decks to houses, and I want to make sure my new deck won’t develop the same problems. Any advice would be appreciated.
A. During my years as a contractor, I replaced countless decks that had exactly the same set of problems as yours. I always marvel that there aren’t more news stories about decks caving in under the weight of moonlight cocktail parties or family reunions. Decks were the rage of the ’70s, but that was also the Dark Ages of proper construction techniques. Before the ’70s, people used redwood and cedar because of their naturally rot-resistant properties (treated wood wasn’t widely available). Redwood and cedar became expensive, so a lot of decks got built from cheaper, conventional untreated lumber or newly developed, inferior treated woods. Remember that thick, paint-like redwood stain? Well, just below the surface, bacteria and fungus were feasting on the new deck as soon as the last nail was hammered home.
Make Sure Your Deck Will Last
A Poorly Built Deck
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A Deck That’ll Last
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After you demolish the old deck but before you start work on the new one, you’ll need to make sure the wood on and in the house is still in good shape. Water leaking around the old deck ledger could have caused significant damage to the house framing. The existing house rim and the lower support walls need to be solid enough to support the multi-ton weight of a deck filled with revelers. After the old deck is removed, you’ll be able to tell if you can still use the house rim. If the wall sheathing behind the rim looks good, you’re styling. But if the sheathing is rotten, investigate further by removing the rotted areas, and check the house’s rim joist and wall framing to see if they’re rotten too. Don’t be too eager to rip apart and replace moist or discolored wood; it may still be intact below the surface. Jam a screwdriver into the wood in several places. If the screwdriver penetrates more than 1/4 in. or so, it’s replacement time.
Replacing rotted-out rim joists and lower wooden support walls can be a huge job. You may want to have an experienced carpenter on hand to help walk you through that gauntlet. To properly attach a deck ledger, follow these guidelines:
Drop the level of the new ledger enough to allow at least a 2-in. gap between the bottom of any doors and the top of the deck boards. That way, water and snow melt won’t be able to accumulate and seep under doorsills to ruin interior floors, and storm doors will swing past ice, snow and leaf deposits (and those bones your dog dragged home from under your neighbor’s deck).
Install metal flashing (drip cap) over the entire length of the top of the ledger. Custom cut and fit another strip of flashing over this drip cap and under doors to cover and protect remaining unflashed areas under doorsills. Caulk the gap between the flashing and the bottom of door thresholds. Install Z-flashing behind the bottom of the ledger and over the siding below. This keeps water from wicking along the bottom of the ledger and getting behind the siding. Leave a 1/8-in. gap between the end of the ledger and the ends of siding and fill it with high-quality exterior caulk to keep water from leaking behind the ends of the ledger.
Anchor deck joists to the ledger with joist hangers, filling each hole with 1-1/4 in. galvanized or epoxy-coated joist hanger nails rated for outdoor use.
Predrill and sink 1/2-in. dia. lag screws in every other joist space, alternating up and down positions to keep the ledger from splitting. Select lag screw lengths that will penetrate the ledger, exterior sheathing and the 1-1/2 in. thickness of the house rim joist (4 in. is usually the right length).
Use only .40 treated wood intended for outside use for all the structural members of the deck, including the ledger, joists, beams and posts.