How a ledger gets attached — the un-skippable layers

An un-flashed ledger lets water sit in the joint between the ledger and the house wall. Over 5-10 years the band joist behind the ledger rots from the inside, completely invisible. The lag bolts end up biting into spongy wet wood instead of structural lumber. The deck looks fine right up until a party load (10+ people on it) pulls the ledger straight off the house. Ledger failure is the #1 documented cause of deck collapse. Per CPSC data, an average of 30+ people die in deck collapses every year — most from ledger failures.

1/2″ diameter hot-dip galvanized lag bolt, minimum 5″ long for a 2× ledger lagged to a 2× rim band (1.5″ ledger + 0.5″ sheathing + 1.5″ band + 1.5″ penetration buffer). Stainless is required for treated lumber that contacts the house wall in coastal/wet climates. Through-bolts (lag head + nut on the interior) are even better when interior access is available — the IRC allows either. Anything smaller than 1/2″ is non-compliant.

Per IRC R507.9.1.3, lag bolt spacing depends on joist span. For a typical 12 ft joist span: lags at 16″ on-center, staggered top + bottom row (one row 2″ down from top edge, the other 2-1/8″ up from bottom). For 14-16 ft joist spans: lags every 13″. Minimum 5/8″ from any edge. The Ledger Board Calculator on DeckMath gives the exact spacing for your joist span + lumber size.

Absolutely not. Siding must be REMOVED before installing the ledger so the lag bolts seat directly through sheathing into the band joist. Lagging through vinyl creates a soft compressible layer between the ledger and the structural frame; the lags loosen progressively as the vinyl cold-flows under load. Hardiplank cracks at the bolt holes. Always cut back siding to bare sheathing, install the 5-layer flashing system, then re-lap siding over the top flashing.

Yes — they do different jobs. The back flashing (self-adhered membrane behind the ledger) is your primary barrier against water that drives sideways into the joint. The top z-flashing is the primary barrier against water that lands on top of the ledger (rain hitting the deck, snow melt). Skip either one and water reaches the band joist within 1-3 years. IRC R507.9.1.4 requires both — "continuous flashing material extending behind the siding above the ledger and beyond the ends of the ledger."

Don't lag into the brick — brick is a veneer, not structural, and lags will pull out under load. Two options: (1) bolt THROUGH the wall with carriage bolts that anchor in the interior framing (requires interior access and a structural engineer), or (2) build a free-standing deck with a beam line where the ledger would be, supported by its own posts and footings. Most pros default to free-standing for brick / stone / stucco houses. Cantilever / strap-on solutions exist but always require engineer review.

No, and this is a common mistake. Construction adhesive between the ledger and the sheathing TRAPS moisture that finds its way past the flashing, accelerating rot rather than preventing it. The 5-layer flashing system is engineered to be vapor-permeable — water that gets in needs a path to dry out. Adhesive blocks that path. Use lag bolts only. The flashing membrane provides the seal you're worried about.