page_title: Cavity wall
section_title: Components
hierarchical_section_title: Cavity wall / Components
caption_attribution_description: English: CMU and Brick Cavity wall Component Section
context_page_description: A cavity wall is a type of wall that has a hollow center. They can be described as consisting of two "skins" separated by a hollow space. The skins typically are masonry, such as brick or cinder block. Masonry is an absorbent material that can slowly draw rainwater or even humidity into the wall. One function of the cavity is to drain water through weep holes at the base of the wall system or above windows. The weep holes allow wind to create an air stream through the cavity that exports evaporated water from the cavity to the outside. Usually, weep holes are created by separating several vertical joints approximately two meters apart at the base of each story. Weep holes are also placed above windows to prevent dry rot of wooden window frames. A cavity wall with masonry as both inner and outer skins is more commonly referred to as a double wythe masonry wall.
context_section_description: A cavity wall is composed of two masonry walls separated by an air space. The outer wall is made of brick and faces the outside of the building structure. The inner wall may be constructed of masonry units such as concrete block, structural clay, brick or reinforced concrete. These two walls are fastened together with metal ties or bonding blocks. The ties strengthen the cavity wall.
  
  The water barrier is a thin membrane that keeps moisture away from the cavity side of the interior wall.
  The flashing component is important. Its main purpose is to direct water out of the cavity.  Metal flashing usually extends from the interior wall through the outer wall and a weep hole with a downward curve allows the water to drain. Flashing systems in cavity walls are typically located close to the base of the wall, so that it will collect the water that goes down the wall.
  Weep holes are drainage holes left in the exterior wall of the cavity wall, to provide an exit way for water in the cavity.
  Expansion and control joints do not have to be aligned in cavity walls.
  In modern cavity wall construction, cavity insulation is typically added. This construction makes it possible to add a continuous insulation layer between the two wythes and, vertically, through the slabs, which minimizes thermal bridges.
caption: Components on a concrete masonry unit (CMU) and brick cavity wall
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