Many builders like to use flashing when installing a ledger. Find out which types of flashing builders use in your area. I tend to use heavy-gauge aluminum behind the ledger, though I sometimes opt for high-quality galvanized sheet metal or even copper—expensive though it is—instead of aluminum. Although it can take a while, ocean air and city smog will gradually take their toll on aluminum flashing, causing it to deteriorate.
The flashing is installed before the exterior siding. It can be nailed directly to the wall framing and rim joist if no sheathing has been used on the exterior walls. Otherwise, install the flashing on top of the wall sheathing (see the illustration at left). Order flashing that is wide enough to extend several inches above the ledger and down over the rim joist. At door openings, cut the flashing just enough to bend it over and lay it flat on the subfloor. Use as few nails as possible when installing flashing, and keep them high on the wall. The ledger and exterior siding will hold the flashing in place. If you install housewrap (such as Tyvek® or Barricade®) over the wall sheathing,
make sure the flashing tucks underneath the housewrap, as shown in the illustration.
In the dry Southwest, the ledger can be fastened directly on top of the flashing. Otherwise, use galvanized washers or PT shims to create a narrow (%-in. to!4-in.) drainage space behind the ledger. This prevents buildup of moisture or mold.
INSTALLING A LEDGER WITHOUT FLASHING.
Here’s how to install a ledger against fiber — cement siding, wooden clapboards, or Tl-11 siding without using flashing. Simply install the siding in the normal fashion, and hold the ledger away from the siding with PT wood spacers or galvanized washers. I’ve installed ledgers this way on a number of houses, including Habitat projects. To account for the angle of wood or fiber-cement clapboards, cut an angled PT spacer or use galvanized washers in the manner shown in the illustration at right. For that technique, first install the spacers, then bolt the ledger loosely in place. Complete the deck framing, then tighten the ledger installation bolts.
Nails won’t do when installing a ledger, though you can drive a few just to hold the board in position. My preference is to attach the ledger with И-in.-dia. bolts that extend through the rim joist and are held fast with nuts and washers. Make sure the ledger is level before you begin boring holes for the bolts. Space bolts 16 in. to 24 in. apart. As extra insurance against unwanted water, apply some silicone caulk in each hole before inserting the bolt through the rim joist. Insert the bolts through the rim joist from the back, making sure you place a washer beneath each bolt’s head and nut.
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Larger decks may require more bolts to attach the ledger to the house frame. You have to think about the weight a deck might carry— a party with 50 people on a deck is a lot of weight.
