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Flashing A Deck Ledger Board Properly
Deck Ledger Board Detail
Lately I’ve been seeing problematic deck ledger 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.
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 and just buy plain metal coil stock.
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I am planning on installing a potch roof over my concrete patio. The ledger board will be installed to the second floor joists. The second floor joints are fabricated wood I beams joists. The ledger will be perpediular to the wood I beam joists. The second floor joist wrapper is sheating not 2X. The house is located in PA. What is the recommended method to attach the ledger board to the ends of the I beam joist and joist wrapper(sheething)?
Regards,
Jeff
@ Jeff – Are you really serious that there’s no structural rim joist attached the the I-Joists? Depending on the manufacturer of your joists that may be a rather significant structural issue. I’d look into that with your builder or local building code official or a local engineer. The rim joist provides structural stability for the I-joists and helps transfer vertical loads from the framing above.
As far as attaching a ledger it would depend on if you have access to the I-joists from below. Do you have access? Do you have any photos?
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Another thing to point out (didn’t see it in the article) is to make sure you don’t nail the deck boards into the band and through the Z flashing, last summer I had to replace all the siding, most of the framing, and detach a second floor wrap around deck because the builder had done this and the flashing failed causing water damaged inside the walls and rotting the entire band as well.
We used a bitchathane membrane behind the rim when we replaced it, was my first time using it.
Also an alternative to the ledger board is using joist hangars instead, some people prefer hangars…
Nice description Todd.
@ Keith – Thanks for that tip. Decks really should have a ledger in addition to the hangers. The hangers shouldn’t be attached directly to the house, mostly due to the fact that there’s not good way to flash the connection. Structurally it’s not a great detail either.
Thanks for all the great info on your site. I plan on adding a small deck this summer. Your technique sounds very good (I just wish I could enlarge the images). My question is how to handle flashing around existing vinyl siding. I will need to cut out the siding to add the ledger board, so what is the best way to extend the flashing up behind the siding without having to remove all the siding from the top down? Also, I have 3/4″ of rigid foam behind my siding. Should I flash from the outer surface of the foam board, or go behind it to the sheathing?
@ Deejay – Thanks for the compliment. First off you’ll want to get yourself a vinyl siding hook that allows you to “unbutton” the siding without taking everything down. This way you can remove the siding up above the ledger board by a couple of courses and install the flashing properly. I would install the flashing behind the foam board directly to the sheathing, then let the foam cover the top of the flashing. Good luck!