Basics of Resisting Water Penetration in Residential Construction
From homeowners to builders, all recognize the desirability of clay brick. Brick can add value to any home or community as long as some simple steps are taken to design and build
it correctly. Every builder seeks to mitigate callbacks, and it goes without saying that water penetration callbacks tend to be costly and dificult to repair. Whether it’s a puddle in the basement or mold on water-soaked sheathing, water is something to avoid in all construction.
Water penetration has been known to lead to premature failure of materials;
moreover, water is a nuisance to homeowners and a headache to builders. The thickness of a single wythe of brick veneer will allow water penetration, so it is designed and constructed as a drainage wall system. Although the bricks themselves may not allow water through them, the brick veneer will—as will other elements in the wall system, such as windows and other items penetrating the wall. Any water that penetrates behind the brickwork must have a way of exiting quickly. So how do you create a drainage system inside of a brick wall construction? The answer is through the proper design and installation of through-wall masonry lashing.
Within a masonry veneer wall, there should be a means to redirect any moisture that has penetrated the oute wythe of the wall as well as ways to then redirect any water back out to the exterior. Foundations and lintels alone cannot be counted on to redire the water in a consistent manner; therefore, lashing should be installed to protect the interior.
Through-wall lashing is an impermeable membrane placed in the wall that extends from the sheathing, across the air space, and all the way to the exterior of the brickwork. One should place lashing at all points where the air space is closed off. Model building codes
require lashing at the foundation, above window and door heads, at window sills, and where the roof of a one-story wing meets a two-story brick veneer wall. Because the expense and dificulty of replacing lashing is considerable, onthe best materials should be used.
Sheet metals, bituminous membrane lastics, and combinations of such materials are suitable for lashing. Aluminum and building felt should not be used. Flashing should extend from the
outside face of the veneer, through the thickness of the brick veneer, across the air space to the backing, and then up at least 8 inches. The lashing should either extend up behind the water-resistant barrier or should be attached to its surface with a termination bar. Flashing held back from the outside of the brick veneer—even just 1/2 inch—could allow water to re-enter the wall. Builders need not be concerned with the lashing breaking bond since wall ties hold the veneer on the house.
Flashing that is punctured will not perform as intended and should be torn out and replaced. Where lashing under a brick course requires more than one piece, lashing pieces should be overlapped at least 6 inches and sealed with compatible mastic.
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