Name: moisture control in masonry cavity walls
Uploaded: 2024-09-12T16:16:29.000Z
Duration: 1 min 20 s
Channel: JoVE

In cavity walls, a minimum separation is maintained to ensure unobstructed cavity drainage.
Often, a continuous drainage mat within the cavity is used to deflect the mortar droppings and facilitate a clear drainage path.
The water entering this cavity moves out through the weep holes spaced appropriately at the cavity&#39;s bottom and placed above the flashings.&#160;
Additionally, vents near the cavity&#39;s top promote air circulation within the cavity and aid in evaporation of cavity moisture.
Flashings can be installed externally to prevent moisture from penetrating the exterior wall, or internally to divert water that enters the cavity back towards the outside.
Internal flashing is installed at the bottom of the cavity and places where the cavity is interrupted.
One end of the flashing is overlapped by a water-resistive barrier provided on the interior wythe, whereas the other end extends beyond the exterior wythe and bends down to form a drip edge to facilitate free fall of water away from the wall.
Sheet metal flashings, asphaltic membrane flashing, composite flashing, and synthetic rubber are the commonly used flashings.

cavity drainage and flashings in masonry walls

Typically, a cavity wall consists of two wythes separated by a gap of at least 2 inches, which may contain insulation while still maintaining a minimum clear space of 1 inch to facilitate adequate drainage. Advanced methods like the insertion of a continuous drainage mat can further reduce this space while ensuring effective moisture expulsion.
Weep holes, strategically placed at the base of the cavity, are critical for draining accumulated water. These openings are created by leaving head joints open, often protected with screens to block pests. Flashings are implemented in two forms: external and internal. External flashings, including metal copings and counter flashings, protect vulnerable areas like parapets and intersections with flat roofs, preventing water ingress. Internal flashings are integrated during wall construction, positioned at potential water entry points like window heads and sills. These flashings catch and direct water toward the exterior via weep holes.
Materials for flashings vary, ranging from durable and expensive metals like copper and stainless steel to flexible, cost-effective options like asphaltic membranes and synthetic rubber. Given the complexity of replacing internal flashings and the relatively low cost of high-quality materials, the use of durable flashing materials is advisable to avoid future expenses related to water damage. Proper installation, including the overlapping and sealing of flashing sections, is vital for ensuring that all moisture is directed outwards.

Cavity Drainage and Flashings in Masonry walls

In cavity walls, a minimum separation is maintained to ensure unobstructed cavity drainage.
Often, a continuous drainage mat within the cavity is used to ...

cavity-drainage-and-flashings-in-masonry-walls

Education

JoVE Core

Civil Engineering

Unit 1

Masonry

KEY TERMS AND CONCEPTS

moisture control in masonry cavity walls

Masonry cavity walls use a gap between two wythes, or wall layers, to help control moisture. The cavity is usually at least 2 inches wide, and it may contain insulation. Even with insulation, a clear space of at least 1 inch is kept so water can drain away. Some walls also use a continuous drainage mat to reduce the needed space while still moving moisture out.

Weep holes are another key part of cavity drainage. These openings sit at the base of the cavity and let collected water escape. They are often made by leaving head joints open, and screens may be added to keep pests out. This simple detail helps the wall release water instead of trapping it inside.

Flashings guide water back to the outside of the wall. External flashings protect exposed spots such as parapets and places where walls meet flat roofs. Common examples include metal copings and counter flashings. Internal flashings are built into the wall during construction and are placed where water may enter, such as above window heads and at sills.

Different flashing materials offer different strengths and costs. Copper and stainless steel are durable, but they are also more expensive. Asphaltic membranes and synthetic rubber are more flexible and less costly. Because internal flashings are hard to replace, using durable materials and installing them with proper overlap and sealing can help prevent future water damage.

Moisture Control in Masonry Cavity Walls

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Masonry cavity walls use a gap between two wythes, or wall layers, to help control moisture. The cavity is usually at least 2 inches wide, and it may contain insulation. Even with insulation, a clear space of at least 1 inch is kept so water can drain away. Some walls also use a continuous drainage mat to reduce the needed space while still moving moisture out. Weep holes are another key part of cavity drainage. These openings sit at the base of the cavity and let collected water escape. They...

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key terms and concepts

Learn how cavity walls drain water with clear spaces, weep holes, and flashing at roofs, parapets, windows, and sills to help prevent moisture damage.

Moisture Control in Masonry Cavity Walls | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Moisture Control in Masonry Cavity Walls

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