The balcony deck should slope away from the building so water drains off instead of ponding and damaging the structure.

A practical thumb rule is to provide a slope of one eighth inch to one quarter inch per foot away from the building, which balances water runoff with usable deck surface. Measure slope using a level and a tape or straightedge, marking the high point at the ledger and the low point at the outer edge, then cut or shim framing to achieve uniform fall. Install a continuous waterproof membrane across the deck running up under the ledger and over the cant strip so water cannot track into the wall assembly, and always terminate the membrane under a properly integrated flashing. Place scuppers or drains at the low edge where run off concentrates and size them to handle seasonal storms; use secondary overflow paths in corners to prevent backup. For finishes that are near impermeable like some tile systems, build a positive slope and use a bonded mortar bed with waterproofing beneath to send water to drains rather than let it sit on joints or underlayment. Regularly inspect for settled joists, blocked scuppers, or membrane blisters and correct small defects before they cause rot or staining.

Three frequent issues are insufficient slope, improper ledger flashing, and blocked or undersized drains, and each has a straightforward fix. If the slope is too flat you will see standing water after rain; correct by adding tapered sleeper strips or reworking the topping to achieve the one eighth inch to one quarter inch per foot fall. If the ledger flashing is missing or improperly integrated, water will enter the wall; open a small section, install the membrane up under the house wrap and behind the flashing and reseal the ledger connection. If drains are clogged or too small water will pond; clear debris, increase drain diameter if needed, and add additional scuppers or a secondary overflow to handle heavy rain.

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