Attach a Deck to a House

To properly attach a deck ledger to your house, follow these guidelines to keep your house dry and the deck solid.

Steps

If geologically applicable, 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 door sills to ruin interior floors, and storm doors will swing past ice, snow and leaf deposits.
Click the photo below to see details of a long lasting 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 un-flashed areas under door sills. 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.