Balcony Flashing: How It Fails and Why SB 721 Inspectors Care

Balcony flashing is the thin sheet-metal or membrane assembly that seals the joint between a balcony's deck surface and the building's exterior wall. When it's installed correctly it lasts decades. When it isn't, water pools at the ledger, rots the wood, and turns a routine SB 721 inspection into a repair project.

What flashing actually does

Every balcony creates a horizontal shelf next to a vertical wall. Water runs down the wall and hits that shelf. Flashing forces the water back out onto the deck surface — and then off the edge — instead of behind the deck coating and into the framing. It's a small detail with an outsized consequence: nearly every SB 721 finding for hidden dry rot traces back to a flashing failure at the wall tie-in.

Common failure modes

• Reverse laps — upper flashing tucked behind lower layers instead of over them
• Missing or short kickout flashing where the balcony meets a vertical wall
• Sealant used as flashing — silicone bead in place of a metal Z-flashing
• Deck coating terminated below the flashing rather than over it
• Corroded fasteners at the ledger causing separation of the flashing leg

What the inspector looks for

A licensed inspector doesn't just look at the deck surface. They check the wall tie-in, the underside of the balcony for staining, the ledger connection, and whether the deck coating turns up the wall behind the flashing. Where the flashing is buried under stucco, moisture readings and thermal imaging usually tell the story.

How it's repaired

Proper repair means cutting back the deck coating and stucco, removing damaged framing, installing new galvanized or stainless Z-flashing lapped correctly with the weather-resistive barrier, then reapplying the waterproof membrane and deck coating. Cosmetic patches over failing flashing buy time — not more than a season or two.