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Barrier wall and cavity wall construction methods: this article describes the two design approaches to keeping water and moisture out of building exterior walls: designing barrier walls (the exterior skin is waterproof) and designing cavity / rain-screen walls (the wall is designed to get rid of water that penetrates it). Here we define and describe these approaches and we illustrate what can go wrong with each of them, leading to building leaks and mold or structural damage. Page top illustration courtesy Carson Dunlop Associates.
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Definitions of Barrier Wall Construction and Cavity Wall Construction
Definition of cavity wall construction: difference between the cavity approach and the rain screen approach
In 2009 when we took this photo, decades of water running down the wall face (from a gutter leak) had led to extensive frost damage to the wall. We left that brick turned on-end as a clue for site maintenance staff but in fact the facilities management crew were well aware of the conditions here.
By 2012 the college had the wall rebuilt. There are two approaches to cavity wall construction: cavity and rain screen. Continuing with help from Williams and Williams:
Many Brick or Stone Veneer Walls are Barrier Walls not Cavity / Rain Screen Walls
The brick walls of the New York home in our photo at below left contain no weep openings. Bricks were laid tight against a solid masonry block wall with "faux" bond courses to the left of the chimney and all stretcher brick courses to the right of the chimney. Walls both left and right of the chimney were constructed with no drainage. Bricks were mortared against the masonry block structural walls of the home with no air space and no drainage provision.
This is a brick veneer on block structure approximately 30 years old. While the mason omitted weep openings, we did not find any evidence of water or frost damage to the brick veneer except at another wall where splash-up from roof spillage had worn mortar joints. This is a barrier wall design, not a cavity / rain-screen wall designed structure.
Traditional structural brick walls such as at the building shown at above right are comprised of two or more wythes [defined below] of brick laid in parallel and reinforced by bond courses at regular intervals. Such walls typically include an air gap between the exterior wythes of brick - the wall outside surface, and the wall interior.
That space allowed water that leaked into the wall to run down the wall interior and drain at the wall bottom - provided that the wall bottom included weep openings or drainage. At BRICK FOUNDATIONS & WALLS we describe the collapse of the structural brick walled building shown at above right.
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Technical Reviewers & References
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