2.2
Masonry Cavity Walls
Cavity walls feature a hollow space between the outer and inner wythes, connected only by corrosion-resistant metal ties. When water seeps through the…
A masonry cavity wall consists of two wythes separated by a hollow space. The outer and inner wythes are connected using corrosion-resistant masonry ties for structural stability.
When water penetrates the outer wythe, it enters the cavity and is collected by a thin impervious membrane called flashing, which is installed at the cavity's bottom and drained out through weep holes.
Additionally, dampproofing material applied on the cavity side of the inner wythe will protect the interiors from water penetration and also serve as an air barrier.
During construction, debris like mortar droppings can block the drainage system, making it crucial to keep the cavity clear. Using mortar deflection material can help avoid blockage of drainage in the cavity.
The cavity facilitates sound insulation and the placement of conduits for utility distribution within a building.
Also, inserting insulating boards of rigid foam plastic in the cavity can provide thermal insulation.
Cavity walls can be load-bearing or non-load-bearing. In load-bearing cavity walls, the inner wythe supports structural loads, while the nonstructural outer wythe is a veneer.
In non-load-bearing walls, the inner wythe provides lateral support to the outer wythe through the masonry ties.
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Q1: What are the two main components of a masonry cavity wall?
A masonry cavity wall consists of two wythes—an outer wythe and an inner wythe—separated by a hollow space. These wythes are connected using corrosion-resistant masonry ties that provide structural stability. The cavity between them serves multiple functions, including moisture management, insulation placement, and utility distribution.
Q2: How does water drainage work in a cavity wall system?
When water penetrates the outer wythe, it enters the cavity and is collected by flashing, an impervious membrane installed at the cavity's bottom. The water then drains out through weep holes. Dampproofing material applied to the cavity side of the inner wythe prevents water from reaching interior spaces and also functions as an air barrier, protecting the building from moisture damage.
Q3: Why is keeping the cavity clean during construction important?
Debris like mortar droppings can block the drainage system, preventing water from exiting through weep holes and compromising the wall's moisture protection. Using mortar deflection material or beveled bed joints helps prevent mortar from entering the cavity. Traditional practices involved placing steel ties to catch droppings, which are then removed, but modern deflection methods are more effective and easier to implement.
Q4: What are the differences between load-bearing and non-load-bearing cavity walls?
In load-bearing cavity walls, the inner wythe supports structural loads while the outer wythe functions as a nonstructural veneer. In non-load-bearing cavity walls, the inner wythe provides only lateral support to the outer wythe through masonry ties, supporting only its own weight. Both configurations use corrosion-resistant ties to maintain structural connection between the wythes.
Q5: How can cavity walls provide thermal insulation?
Rigid foam plastic insulating boards can be inserted within the cavity space to provide thermal insulation and mitigate heat transfer through the wall assembly. This placement leverages the existing hollow space without requiring additional structural modifications, making it an efficient method for improving the building's energy performance while maintaining the cavity's drainage and moisture management functions.
Q6: What additional functions does the cavity space serve beyond moisture control?
Beyond moisture management, the cavity facilitates sound insulation, reducing noise transmission through the wall. It also provides space for placing conduits and utilities for building distribution systems. The hollow space allows for flexible routing of electrical, plumbing, and mechanical systems without compromising the structural integrity of the masonry wythes.
Q7: How do masonry ties contribute to cavity wall performance?
Corrosion-resistant masonry ties connect the outer and inner wythes, providing essential structural stability and lateral support. In non-load-bearing walls, ties support the outer wythe's weight and resist lateral forces. Their corrosion resistance ensures long-term durability and prevents deterioration that could compromise the wall's structural integrity and the connection between wythes.