Improper Deck Flashing Problem

Today’s post comes from a reader who asked me to look at a deck flashing problem that he had. The email stated: I’m wondering if you can help me with a problem I am having repairing or replacing the flashing for a replacement deck attached to a stucco house. The original flashing was poorly installed by the builder and over the years has led to wood rot which attracted carpenter ants. The ledger board has been removed and the affected rim boards replaced, but I’m now left with a flashing which needs to be corrected.

The sketch was provided by the homeowner and it shows how the existing deck was flashed. The problem jumped right out at me as soon as I saw this sketch. The flashing starts out great, it’s up behind the siding (in this case stucco) and it prevents water from getting behind the stucco. But that’s where the flashing stops working and it doesn’t do anymore good. As you can see in the photo the remaining flashing is quite short.

For flashing to be effective in this application it must go under the decking and over the ledger board (see How To Properly Flash A Deck Ledger Board for more information). The question here is how to fix this problem before the new deck is built.

Add Additional Flashing
The first step should be to apply a layer of self adhering bitchethane to the house rim joist (all of the exposed wood). The next step will be to add an additional piece of aluminum flashing. The flashing should be tucked up behind the existing flashing as far as possible and then bent up/out similar to the configuration of the existing flashing as it appears in the photo.

Install The New Ledger Board
Next install the new ledger board. It would certainly make sense to use a pressure treated piece of lumber for this item regardless of what material the homeowner chooses for the deck. It’s important to counter-sink any fasteners into the ledger board and then caulk the holes with a silicone caulking.

Install Deck Framing
The deck should next be framed into the new ledger board. I find using triple coated galvanized joist hangers the best approach for this situation.

Finish Flashing
The next step would be to bend the flashing down along the face of the ledger board. You’ll need to cut the flashing at each floor joist in order to get the flashing between joists to bend down.

Install Decking
Finally install the decking on top of the flashing where the deck meets the house. I also recommend leaving a gap between the house and first piece of decking. This allows air to get into that space and dry things out.

If you follow this method the deck and house interface should perform very well for years to come.

Related posts:

1. Flashing A Deck Ledger Board Properly
2. National Enjoy Your Deck Day
3. Mold Growing On North Facing Deck
4. Deck Makeover for Early Fall Entertaining
5. Porch and Deck Footing Types

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