Drainage Planes and Weep Holes in Brick Walls

By Nate Rogers, E.I.T. | November 19, 2019

Let’s start with something simple; we want our buildings to be dry on the inside. Now let’s take that idea one step further; we want our walls to be dry on the inside. Water trapped in a wall will inevitably lead to mold, pest intrusion, rot, or any combination thereof. Moisture control is an important consideration for any type of building, but masonry buildings present an increased challenge due to the many layers of materials. There is a misconception that a brick wall is waterproof. A brick wall will present some protection from weather on the exterior surface, but it is far from waterproof. Even the best bricklayer cannot create a perfectly sealed wall. Water can enter cracks as small as 1/100th of an inch so gaps in the mortar, small ledges and other imperfections in the brick will allow water to get through. Furthermore, some brick is highly porous and acts like a sponge soaking up water during a weather event.

If the exterior layer of brick can’t keep water out, how can we keep the inside of our wall dry? The first step is accepting the simple fact that water will always eventually get behind the exterior brick. We can reframe that initial question; how can we get water out of the interior layer of the wall before it rots the wooden components behind it? The simple answer: drainage planes and weep holes.

Weep holes are holes or gaps along the bottom of the brick veneer which allow water to drain out from the wall. These holes also serve to provide ventilation in the air gap behind the brick veneer. Ventilation can help to dry out the interior wall layers after a weather event. Allowing air behind the brick veneer also helps to equalize the pressure and limit the penetration of wind driven rain into the wall cavity. Typically, these openings are simply a void in a vertical mortar joint and spaced between 24” and 36” horizontally along the bottom of the wall. Notice in the graphic the importance of proper installation of flashing and building wrap. These two wall elements act as a barrier and ensure that any water in the wall cavity travels down and towards the weep holes without soaking into the foundation wall or interior wall elements. Open weave mesh should also be considered when designing a detail for a brick veneer wall. During construction, mortar can fall into the wall cavity and can block weep holes. This mesh prevents that fallen mortar from directly blocking weep holes while still allowing water to drain. Small inserts of this mesh can also be inserted directly into weep holes to provide protection against insects, rodents or other pests from entering the wall cavity without hindering water drainage.

One can imagine the potential of water buildup in the wall cavity without weep holes for drainage. Large water buildup could lead to mold growth, rot of interior wall elements, or rust of mechanical fasteners. Some homeowners have made the mistake of filling in weep holes thinking the gaps were mistakes made by a brick layer. Without the proper drainage or ventilation, a building’s structure can easily be compromised. Fortunately, if you discover a brick, masonry, or even landscape retaining wall missing weep holes, there are ways to repair it. Homeowners should consider working alongside a professional to design an appropriate solution for their situation. Give us a call today and we can help you design the right weep hole detail for your building!

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