Field note
Weep Screed Basics for Your Next Project
What Is Weep Screed?
A weep screed is a piece of metal flashing fastened to the bottom of the exterior stucco wall.
It’s perforated with small holes to wick excess moisture away from the bottom of the walls below the foundation plate line to prevent water damage.
How Does Weep Screed Work?
A weep screed is more than a hilariously named piece of building material with a bend and lots of holes to allow water to drain through. It’s an invaluable part of the stucco application process.
Proper application can be the difference between a building lasting hundreds of years, or one that’s destined to rot away and fall apart.
The Functions of Weep Screed
A weep screed has one primary function. To allow moisture to flow through the bottom of a stucco wall to prevent water damage to the building structure.
Weep
The “weep” function of weep screed basically means to drain excess moisture. Exterior walls and windows often have a small weep hole built into them to allow water drainage. The small holes that run along the bottom edge of a weep screed function the same way.
A stucco wall system tends to absorb water, most of which evaporates. Some of the water gets trapped along the back of the stucco membrane by the exterior lath.
Because of gravity, water will run down the stucco walls. Without a specific place to drain, the excess moisture can wreak havoc on the home.
Screed
The stucco or plaster is applied to wire-mesh metal lath on water-resistant building paper in either two or three coats. The weep screed functions to “screed,” or to create a level surface.
The metal piece gives a solid location at the bottom of the walls for the stucco to adhere to just below the foundation plate line. That’s why it may sometimes be referred to as a foundation weep screed.
Weep Screed for Moisture Control
Water buildup along the back of the stucco membrane can cause numerous problems. Your stucco could bubble and crack. Mold could grow, or water could leak into the walls of your home.
With a wood-constructed building, water could damage the framed walls and structural members where rot could occur. Installation of a weep screed helps to stop problems from occurring while also creating a flush surface for the exterior wall.
A weep screed creates a flat, true screed surface at the base of stucco walls and lets excess moisture drain away from the material.
Is a Weep Screed Necessary
While you’ll likely find conflicting answers to this question, a weep screed is an important part of any stucco application.
Not only does is the weep screed important for moisture drainage and critical to stucco maintenance and upkeep. The screed also provides an easier and more aesthetically pleasing stucco application.
In most counties, building codes require a weep screed. Be sure to check with your local municipality for proper installation guidelines.
Here’s an excerpt from the 2012 International Building Code regarding weep screeds –
“A minimum 0.019-inch (0.5 mm) (No. 26 galvanized sheet gage), corrosion-resistant weep screed or plastic seep screed, with a minimum vertical attachment flange of 3.5 inches (89 mm) shall be provided at or below the foundation plate line on exterior stud walls in accordance with ASTM C 926. The weep screed shall be placed a minimum of 4 inches (102 mm) above the earth or 2 inches (51 mm) above paved areas and shall be of a type that will allow trapped water to drain to the exterior of the building. The weather-resistant barrier shall lap the attachment flange. The exterior lath shall cover and terminate on the attachment flange of the weep screed.”
Where to Use a Weep Screed
Weep screeds should be used with newer construction where stucco is placed over wood. Excess moisture buildup at the back of the stucco membrane in wood construction could rot wooden lath on top of the usual leaks and cracks in your stucco.
Weep screeds are also sometimes used on walls with stone veneers.
Weep screeds may not be necessary if you’re applying stucco to match an existing building without a screed. In this instance, be sure to get an exemption to comply with industry standards and local building codes.
If your building has concrete or CMU walls, weep screeds won’t be necessary. These materials can handle water without problems, which is why weep screeds in stucco walls are installed to drain onto concrete foundations.
There’s a way to determine if water is leaking into your home from behind a stucco wall. A standard test method is to perform a Stucco Wall Penetration and Weep Screed Leak Detection Test.
With this simple test, you’ll receive home inspection reports showing any water intrusion, damage to the structure behind a stucco wall, and determine if further repairs are necessary.
Tips for Purchasing Weep Screed
Weep screed can be purchased at retailers like Home Depot or Lowe’s, but it’s a toss-up on whether either location will have multiple options or any availability.
Types of Weep Screed
These large retailers will probably have ⅞” three-coat weep screed, but likely only in one of the two flashing types: 7 and J.
Type 7
The #7 weep screed has a V-shaped bend in the bottom of it, which looks something like an upside-down 7.
This is a more common type of weep screed and can typically be found in older buildings. If you’re able to find a weep screed at Lowe’s or Home Depot, it will most likely be a #7.
J-Type
The J-type is less common than the #7 and will mostly be found at stucco supply yards. The flashing has a simple curved bend at the bottom, giving the metal its “J” shape.
Where to Purchase Weep Screed
The best choice for purchasing a weep screed will be at a stucco supply yard. Not only will they have all the material for stucco installations, but they’ll have a variety of options for two-coat or three coat stucco systems.
If you’re a General Contractor hiring a plaster sub-contractor, they will typically buy weep screeds at specially building supply yards, rather than big-box retailers.
Staying Up to Local Codes
As mentioned above, most counties will have specific codes in place for weep screed. Depending on where you live, there will be different standards for installation overlaps and clearances.
Some locations have codes that specify the sizes of the ground flange for a weep screed. When looking up your local codes, be sure to find flashing that adheres to those codes so you’ll pass inspection.
Certain codes may also require a specific type of corrosion-resistant weep screed.
All of the above versions of a weep screed will usually be stocked at your local stucco supply yard.
Different Names for Weep Screed
While the screed is just a piece of metal with a bend and holes in it, the jargon behind the name can be somewhat confusing.
Screeds can sometimes be called foundation weep screed or stucco weep screed. All of these serve the same purpose and are the same type of flashing.
The key to look for is the type of metal and sizing to comply with local codes. Otherwise, a weep screed, either a #7 or J-type, all serve the same function.