Flashing A Deck Ledger Board Properly
Written by Todd Fratzel.
Deck Ledger Board Flashing Detail
Lately I’ve been seeing problematic deck ledger flashing details so I’d like to share with you my perspective on how to properly flash and secure your deck to the house. Properly flashing a deck ledger seems to be a lost skill with most weekend warriors…..let’s discuss how to properly secure the deck ledger and install the flashing.
Building a new deck isn’t really that difficult of a project. However, there are some details that must be followed in order to prevent premature failure of your deck and the area of your house that it’s attached to. The problem with attaching a deck to the house is it creates a great area to collect water. The intersection of the house and deck is extremely vulnerable to moisture problems.
As you can see from the diagram and the photo flashing must be done in layers. The best way to think about it to visualize what a drop of water will do as it hits the deck and moves towards the house. First the rain hits the siding, then it gets to the house wrap, then it hits the drip cap flashing and runs out away from the house.
How To Flash A Deck Ledger Board
First I like to install a layer of self adhering bitchathane (we like Grace Ice and Water) behind the ledger and above it by at least 12 inches. Make sure the bitchathane is behind the house wrap. The house wrap should extend and overlap the bitchathane.
Next mark the location of the bottom of the ledger board and install a small piece of z flashing. When I bolt the ledger board to the house, I like to install 3 or 4 flat washers between the house and the ledger to allow water and moisture to escape and not get trapped. I’d also like to point out that I prefer bolts to lag screws. The reason is lag screws don’t hold very well when then only penetrate and inch or so into the rim joist. Make sure you seal all around the bolt heads with some silicone caulking as another line of defense against water.
Next you’ll want to install a piece of metal drip cap flashing above the ledger board. When you install the floor joists you’ll need to make some small cuts in the flashing to allow the top of the joist to line up with the top of the ledger board. Make sure the house wrap is long enough to cover over the top of the drip cap. (This is a bit different than the photo.) If there is already house wrap on, then cut a slit in the house wrap just above the top of the ledger. That way you can slide the drip cap up under the house wrap. Just remember it’s all about layering.
Finally you can install the decking. The siding above should terminate slightly above the surface of the decking to allow air into the space. Just remember, if water gets into that intersection it’s now going to follow the plane of the drip cap and be pushed out away from the house. If you follow these steps the next time you install a deck you’ll be sure to eliminate a premature failure due to excess moisture and rotting.
Alternate Detail for Masonry Siding
If you have brick siding then you need to use a slightly different approach. Below is a sketch showing a section of the brick wall. The steps are as follows:
- Grind out the grout along a row of bricks.
- Fabricate copper flashing. The flashing has two details worth pointing out. On the end that will fit into the mortar joint bend a very small hem that will act as a wedge. On the lower exposed side bend a standard hem.
- Insert the flashing into the mortar joint so that it fits tightly with the wedge.
- Seal the joint with a high quality flexible caulking.
If you’re planning on building a new deck get yourself the Complete Guide To Decks.
If you want to make your own flashing you can purchase a Tapco 10558 PRO 19 10-Foot-6-Inch Wide by 19-Inch Throat Portable Brake
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