Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.

The Science of Drainage: Why Weep Screed Holes Are Non-Negotiable

There is a fundamental misunderstanding among many homeowners in Southern California: the belief that stucco is waterproof. It is not. Stucco is a cementitious reservoir that absorbs moisture. Whether from a heavy Newport Beach rainstorm or dense marine layer fog, water will permeate the surface.

A compliant stucco assembly relies on a "drainage plane"—typically two layers of Grade D building paper—behind the cement. Gravity pulls this moisture down the wall until it hits the termination point. This is where the Weep Screed functions as the most critical component of your home’s waterproofing defense.

1. The Mechanics of the Weep Screed

According to ASTM C1063 (Standard Specification for Installation of Lathing and Furring), a foundation weep screed must be installed at the bottom of all exterior stucco walls . It serves two primary technical functions:

• Straight Edge (Depth Gauge): It provides a rigid ground for the plasterer to ensure a uniform thickness (typically 7/8" for three-coat systems).
• Moisture Ejection: The holes punched into the bottom flange allow trapped water to escape the wall cavity rather than pooling and rotting the framing plate or shear wall.

2. Identifying Your Hardware: Type #7 vs. "J" Metal

Not all termination metals are created equal. In our inspections across Orange County, we typically encounter two profiles:

The #7 Foundation Weep Screed (The Standard)

This is the superior choice for drainage and is widely recognized in the industry. It features a V-shaped slanted leg that extends 3.5 inches up the wall.

• Design: The V-shape ensures that the building paper overlaps the metal correctly, directing water out effectively.
• Redundancy: It usually has holes on both the front and back of the V-channel. If paint clogs the front holes, the back channel still allows water to weep out beneath the edge.

The "J" Weep (The Low Profile)

Often confused with a plaster stop, a true J-weep has holes along the bottom ridge but lacks the slanted drainage leg of the #7. While it offers a cleaner architectural line, it is more susceptible to clogging and offers less drainage capacity.

3. The Homeowner’s Dilemma: Pests vs. Physics

We frequently field calls from homeowners asking: "Can I caulk these holes to stop ants or termites from getting in?"

The answer is an absolute NO.

Sealing weep holes creates a "bathtub effect" inside your wall assembly. The building paper will eventually degrade, and the standing water will destroy the wood framing. The cost of structural rot repair far exceeds the annoyance of pests. Instead of caulking:

• Exterior Perimeter Sprays: Rely on chemical barriers applied by pest control professionals.
• Weep Screens: Specialized retrofit screens are available that allow water out but keep insects out, though these can be difficult to install post-construction.

4. Retrofitting Holes: Proceed with Extreme Caution

If you identify that your home was built with a hole-less plaster stop at the foundation, you might be tempted to drill relief holes yourself. This is risky.

To establish drainage without compromising the system:

• Precision is Key: You must drill through the metal flange only. If the drill bit punctures the waterproof paper or the flashing membrane behind the metal, you create a direct injection point for water into the studs.
• Sizing: The industry standard suggests a minimum hole diameter of 3/16" to prevent water tension from bridging the gap and to allow debris to flush out.

5. Critical Code Clearances: The Foundation Gap

Codes (CRC/IBC) dictate strict clearances for the bottom of the weep screed to prevent moisture from wicking up from the ground (capillary action) and to allow drainage. These clearances are mandated by code :

Maintenance Note: While you must never caulk the holes in the screed, you generally can seal the gap between the metal screed and the concrete foundation below it to prevent pests from entering the sub-area, provided the caulk does not lap up over the weep holes.