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Weep openings provide drainage in this brick wall (C) Daniel FriedmanWeep Holes, Drainage & Moisture Ventilation in Brick Veneer Walls
Masonry veneer wall drainage details & specifications, defects & inspections

  • BRICK WALL DRAINAGE WEEP HOLES - home - CONTENTS: Definition & explanation of brick wall weep holes or weep openings used to provide drainage for the building wall or shell: shell drains & wall drains.
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Weep holes in brick walls:

Here we give construction specifications & details for proper location, flashing, & protection of weep holes or drain openings & vents in brick or other masonry veneer walls. We explain how these weep or vent openings in brick walls work, where and how they should be installed, and what special products such as opening screens & flashings are available.

This article series explains the purpose of drainage openings & rain screens in solid brick walls and in some brick veneer walls: brick wall weep holes and recommends their use in new construction and in some brick wall repairs or retrofits. Weep holes in building exterior masonry walls (brick or stone) are a drainage system that is used in cavity wall or rain-screen wall construction methods to get rid of water that has penetrated the outer wall skin or surface.



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Weep Holes in Brick Veneer & other Masonry Veneer Walls

Flemish bond brick wall, Vassar College (C) Daniel FriedmanBrick veneer construction [and some other masonry veneer construction such as thin stone over wood framed walls] incorporates a drainage cavity to deter water penetration into the building. This air space creates a physical separation between the brick wythe and the inner steel stud wall.

When the wind-driven rain penetrates the veneer wythe, the cavity allows the water to drain down the back face of the brick. This water is then collected at the base of the wall by flashing and channeled out to the exterior through weep holes. (Arumala 2007)

Watch out: Both structural brick walls and veneer brick (or stone) walls may be designed either as a barrier wall or a cavity/rain-screen wall. Before you can evaluate the condition of a wall you need to understand how it was built and whether or not the as-built matches the as-designed conception of the wall.

Our page top sketch, courtesy of Carson Dunlop Associates, a Toronto home inspection & education firm, shows both the reasons for and the typical design details used in weep openings on brick walls.

[Click to enlarge any image].

The beautiful Flemish-bond structural brick wall (left) on the Vassar College Campus was constructed with very subtle drain or weep openings at the wall bottom. It has survived intact even though the building is located in a seasonally wet and freezing climate.

Article Series Contents

Watch out: In February 2016 in the U.K. The Telegraph reported that the Cavity Wall Insulation Victims Alliance (CWIVA) was lobbying both industry and government to obtain relief from insulation companies who were selling this bad approach to building energy savings by representing that their insulation was "government-backed" - it was not and it is not.

Some of these news reports "mould in wall cavities is caused by insulation" describe a real problem but do not necessarily offer a correct explanation of the cause of the mould contamination. Insulation does not itself cause mould growth. Mould spores are present everywhere, all the time, in air. But when conditions are right, particularly trapped moisture and perhaps temperature, mould growth will be encouraged in and on buildings.

Since the mid 1980's building scientists have known stressed that air leaks into and out of wall cavities at penetrations (openings for receptacles, switches, wires, pipes) is a particular source of moisture problems.

If we combine leaks or moisture with improper placement of insulation, such as pumping or blowing styrofoam bead or other insulation into the air space between a brick veneer wall and the building's structural (usually wood-framed) wall, then yes, that's a recipe for trouble. Brick veneer walls are not waterproof and must be designed to permit water to drain out of the wall rather than into the wall interior.

This article provides details about the importance of providing proper drainage for brick veneer walls.

Definition & Images of Veneer Wall or Masonry Wall Weep Openings

Under-sized and blocked weep openings (C) Daniel Friedman

Weep openings are drainage holes left in the face of a brick veneer wall [and possibly some other constructions] in order to allow water that has penetrated the wall to escape downwards through the wall cavity and out to the exterior of the wall surface through the weep openings. As will be explained later, I think the weep openings in the veneer wall shown above, though properly located, are probably not working.

This escape passage and wall design are a method for reducing water intrusion into the structure interior. According to the Masonry Design Manual, weep holes are

Openings placed in mortar joints of facing materials at the level of flashing, to permit the escape of moisture, or openings in retaining walls to permit water to escape.

Above we illustrate the most basic brick wall weep opening.

To diagnose a building water entry or moisture problem originating at its exterior walls we must first understand the construction concepts that were used to build that wall: two very different concepts apply, though they often appear mixed or even confused in buildings: barrier wall construction methods (the wall exterior skin keeps out water) and cavity or rain-screen wall construction (the wall is designed to handle and get rid of water that penetrates the outer skin).

See WALL CONSTRUCTION BARRIER vs CAVITY for definitions and explanations of barrier wall construction compared with cavity / rain screen exterior wall construction methods, objectives, and damage vulnerabilities.

Below we show a brick wall (a veneer in this case) with weep openings at regular intervals at two heights above ground level.

Cracks in brick veneer wall (C) Daniel Friedman

Below is a close up of one of the drainage openings.

Cracks in brick veneer wall (C) Daniel Friedman

Veneer wall weep or drain openings are placed at least at the very bottom of a brick veneer wall cavity and sometimes as vents openings are placed higher in the wall in some designs.

For the wall shown in the photos just above, we suspect that an air space behind the veneer does not extend lower than the weep holes in our photos. Why? The lower wall is solid masonry construction with no air space rather than frame construction. The lower brick courses were laid tight, with no cavity at all, against a solid concrete or masonry block foundation wall, thus forming a solid composite masonry wall.

Typical Construction Specification for Brick Veneer Wall Containing Weep or Drain Openings & Wall Cavity Vents

Here are three examples of wall cavity vent and weep opening specifications adapted from the Brick Industry Association (BIA), our industry expert source, and from two example construction specifications for brick veneer walls that offer more details.

Note: the specifications for any particular building project should be made by a qualified design professional such as a licensed professional engineer or licensed architect.

Weep Hole Wall Vent Construction Specification Example #1 - BIA

The Brick Industry Association recommends veneer wall weep opening specifications as follows:

Weeps:

Under-sized and blocked weep openings (C) Daniel Friedman

Above, these weep openings are properly located: above the upper surface of the wall bottom flashing, and they might meet the BIA's 3/16" (4.8mm) diameter, but in my opinion they are inadequate.

At BRICK VENEER WEEPS BLOCKED or MISSING we show that these tiny tubes inserted as veneer wall drains were mostly blocked by mud placed by mud-dauber wasps. Little wall-bottom tubes are also very easily blocked by falling mortar and debris in the wall cavity. Good location, weak weeps.

At BRICK WALL DRAINAGE, FLASHING, VENTILATION PRODUCTS we illustrate a taller, blockage-resistant PVC product that provides better veneer wall drainage opening protection, letting water out while preventing insect intrusion.

Weep Hole Wall Vent Construction Specification Example #2

  1. Wall shall use pre-formed control joints using rubber material. Provide with corner and tee accessories and fused joints.
  2. Weep openings: use molded PVC grilles that are insect resistant, located above-grade and not blocked
    1. Install weeps in veneer walls at 16" (400 mm) on center horizontally above through-wall flashing, above shelf angles and lintels and at bottom of walls
    2. Install cavity vents in veneer walls at 16" (400 mm) on center horizontally below shelf angles and lintels and at top of walls.
    3. Install cavity mortar diverter at base of cavity as recommended by manufacturer to prevent mortar droppings from blocking weep/cavity vents.
    4. Do not permit mortar to drop or accumulate into cavity air space or to plug weep/cavity vents.
  3. Wall cavity mortar control: Semi-rigid polyethylene or polyester mesh panels, sized to thickness of wall cavity, and designed to prevent mortar droppings from clogging weep openings and cavity vents and designed to allow proper cavity drainage

Venting a Veneer Wall Supported on a Foundation

Brick veneer wall weep opening & other details adapated from BIA Tech Notes 28B Fig 1 as in Arumala 2007 (C) InspectApedia.com 2016

[Click to enlarge any image]

Above: Brick veneer wall construction details showing weep openings immediately above flashing that is in turn atop bottom brick course of a brick veneer wall constructed over a steel stud cavity wall. These details are for a brick veneer wall that rests atop a masonry foundation.

This illustration is adapted from BIA Technical Notes 28B, Figure 1 as used in Arumala 2007 cited below. Critical wall bottom flashing is shown in red, brick veneer weep opening locations above the horizontal portion of that flashing are shown in green, and house-wrap / water barrier fabric(s) are shown in dark gray.

Watch out: Less evident in our sketch but important: the water barrier affixed to the wall sheathing should extend over the top of the wall bottom flashing, not behind it. Otherwise water in the wall cavity may pass behind the bottom flashing and thus will fail to drain from the wall cavity.

Venting A Veneer Wall Supported by Steel Lintel

Below: Brick veneer wall construction details showing the location of weep openings immediately above wall bottom flashing that is in turn immediately above the upper surface of the supporting steel lintel in a lintel-supported brick veneer wall design.

Brick veneer wall weep opening location details at the supporting steel lintel, adapted from Arumala (2007) (C) InspectApedia.com

[Click to enlarge any image]

Notice that when the brick veneer is supported by a steel lintel, the weep openings are immediately over the wall bottom flashing that is in turn immediately over the upper surface of the supporting steel lintel. This illustration is adapted from Figure 3, "A Typical Section of a Brick Veneer Wall with Steel Stud Backup Wall" - Arumala (2007)

Weep openings & vents in upper levels of brick veneer walls

Cracks in brick veneer wall (C) Daniel Friedman

As our photograph above illustrates, in tall brick veneer walls additional weep openings and air vent openings may be specified by the architect/engineer for placement higher in the wall.

Air, Cavity & Weep Hole Wall Vent Specification Example #3

  1. Air Vents: Flexible ultra violet resistant polypropylene co-polymer DA1006 Cell Vent by Dur-O-Wal Inc., 7777 Washington Village Dr., Ste. 130, Dayton, OH
    45459, (888) 977.9600, www.dur-o-wal.com.
    1. Size: Height 2-1/2 inch maximum except as indicated otherwise, by full width of brick.
    2. Color: To match mortar color.
  2. Weep Vents: Flexible ultra violet stable recycled polyester mesh, rectangular shape by Mortar Net USA Ltd, 541 S. Lake St., Gary, IN 46403, (800) 664-6638,
    www.mortarnet.com, CavClear Weep Vents by Archovations, Inc., PO Box 241, Hudson, WI 54016, (888) 436-2620, www.cavclear.com.
    1. Size: Height 2-1/2 inch maximum except as indicated otherwise, by full width of Brick.
    2. Color: To match mortar color.
  3. Cavity Wall Mortar Net: Lightweight polyethylene, 90 percent open woven mesh by Mortar Net USA Ltd, 541 South Lake Street, Gary, IN 46403, (800) -664-6638,
    www.mortarnet.com. or CavClear Masonry Mat by Archovations, Inc., PO Box 241, Hudson, WI 54016, (888) 436-2620, www.cavclear.com.
    1. Size: Height 10 inches, thickness as required to fill cavity.
    2. Size: Full height of wall, thickness as required to fill cavity
  4. Weep Holes:
    1. Form weep holes in mortar joints of exterior wythe of cavity walls at bottom of cavity over foundations, bond beams, through wall flashings, and other water stops in wall.
    2. Form weep holes by leaving head joint free and clean of mortar, and raking out bed joint at weep hole.
    3. Space weep holes approximately 24 inches oc. Keep weep holes free of mortar droppings and other obstructions.
  5. Pointing & Cleaning at End of Wall Construction
    1. At completion of masonry Work, fill holes in joints (except weep holes) and tool.

Brick Veneer Wall & Curtain Wall Venting & Research

Where do the Brick Wall Drainage Openings (Weep holes) Belong?

Where do the brick wall weep holes go? This topic has moved to a separate article now found at BRICK VENEER WALL WEEP HOLE LOCATION

Tamlyn brick weep hole cover (C) Daniel FriedmanDamaged Brick Veneer Walls - Blocked or Missing Brick Veneer Weep Openings

Details of this topic are now at BRICK VENEER WEEPS BLOCKED or MISSING.

Not All Brick Veneers Lacking Drainage are Damaged - Some of these are Barrier Walls not Cavity / Rain Screen Walls

Brick Veneer Wall Through-Ventilation - Airflow Removes Moisture?

This discussion has moved to BRICK VENEER WALL THROUGH-VENTILATION

Brick Veneer Wall Leakage Problems in Buildings Exposed to Flooding

Please see the new article at BRICK VENEER WALL LEAKS in FLOOD PRONE AREAS

Guide to Brick Wall Drainage Opening, Flashing & Ventilation Products

Please see BRICK WALL DRAIN, FLASHING, VENT SOURCES

Shown above: A Tamlyn Building Products brick vent screen discussed in the article linked-to just above.

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Continue reading at BRICK VENEER WALL WEEP HOLE LOCATION or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BRICK WALL THERMAL EXPANSION CRACKS

Or see STUCCO WALL WEEP SCREED DRAINAGE

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