Wall Base Flashing

March 10, 2023

What is wall base flashing? Well, it is never seen but especially important in the water management in the exterior wall of your house. Simply stated, flashing is installed at the bottom of the wall behind brick or tile masonry and usually polyethylene (plastic) material. As discussed in other HOUSETIPS articles, rainwater passes through brick, stucco, and lap board siding and ultimately winds up at the bottom of the wall. That’s where you need proper base wall flashing.

Proper Installation

The most common use of this flashing is behind brick veneer at the bottom of the wall. The flashing is installed horizontally on top of the brick ledge, or below the brick and then turned up the wall and attached to the wall sheathing. The weather barrier is then lapped over the top.

The purpose of the wall flashing is to collect water that drains down the water barrier and discharge the water through the weep holes in the brick veneer or tile masonry.

Improper Installation

The most common form of improper installation of the wall base flashing is placing the vertical leg of the flashing against the studs of the wall instead of the exterior of the sheathing. At that point, the sheathing – be it plywood, OSB, exterior gypsum wallboard, or other sheathing type – is incorrectly installed on the outside of the wall base flashing and is not code compliant.

With this improper installation, the sheathing becomes subject to rot, decay, and promote biological growth.

Problems Caused by Improper Wall Base Flashing

Common problems with improper installation of the base wall flashing may be water intrusion into your house, biological growth in the wall, and/or musty, damp odors in your house. Since this problem is hidden and out of site, damage from this condition can develop undetected for extended periods of time.

If you suspect this condition is creating problems in your house, consult with a qualified building professional or a licensed contractor experienced in building construction. Be aware that the wall system may need to be disassembled to investigate this condition.

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