Written by Stucco Champions — Southern California’s Authority on Exterior Plastering.
Weather-Resistiant Building Paper: Protecting Your Stucco System from the Ground Up
When installing a stucco system, success starts with the layers you don’t see. One of the most critical components is Weather-Resistant Building Paper (WRBP)—a moisture barrier that protects your structure from water damage and ensures your stucco finish lasts for decades.
Stucco is a reservoir cladding; it absorbs water by design. The only thing preventing that water from rotting your framing is the Grade D paper behind it. This guide explains the physics of the drainage plane and why code compliance is non-negotiable.
1. What Is Weather-Resistant Building Paper?
WRBP is a specially engineered asphalt-saturated kraft paper installed between your home’s exterior sheathing and the stucco. It performs a dual function:
- Water Intrusion Protection: It acts as a drainage plane, redirecting bulk water that penetrates the stucco down to the weep screed.
- Wall Breathability: Unlike plastic vapor barriers, Grade D paper allows trapped water vapor to escape from the inside out, reducing the risk of rot and mold (The "Sweating Wall" effect).
2. Understanding the Two-Layer System
In climates like California’s, building codes (CRC and IBC) mandate a Two-Layer WRBP System over wood sheathing. This isn't redundant; it's structural.
| Layer | Function |
|---|---|
| First Layer (Inner) | The true moisture barrier. It stays separate from the stucco, protecting the wood sheathing. |
| Second Layer (Outer) | The "Sacrificial Layer." It bonds to the wet cement during application, essentially becoming part of the cladding. |
The separation between these two layers creates a Drainage Plane. If you only use one layer, the stucco fuses to it, eliminating the path for water to drain. The two-layer system ensures water always has a way out.
3. Installation Best Practices
Even the best paper fails if installed incorrectly. We follow strict ASTM protocols to ensure the envelope is watertight.
| Technique | Purpose |
|---|---|
| Shingle Overlap Method | Upper sheets must overlap lower sheets to guide water downward and outward (Gravity Flow). |
| Flashing Integration | Paper must tuck under window head flashing and over the sill flashing to prevent leaks. |
| Horizontal Overlaps | Minimum 2 inches (Head Lap). Prevents water from wicking up between sheets. |
| Vertical Overlaps | Minimum 6 inches (End Lap). Ensures sealing at the end of rolls. |
| Weep Screed Lap | The bottom edge of the paper must overlap the metal weep screed flange. |
4. Common WRBP Mistakes to Avoid
When we inspect failed stucco, we often find these critical errors:
Installing a lower sheet over an upper sheet creates a "cup" that catches water and funnels it into the wall. Always work from the bottom up.
- Using "Housewrap" Alone: Standard Tyvek bonds to stucco. If you use housewrap, you must add a layer of Grade D paper over it to act as a bond breaker.
- Skipping the Inspection: Tears happen during lathing. We inspect the paper for rips before applying cement and patch them with moistop sealant or tape.
Conclusion: The Invisible Hero
You will never see the building paper once the job is done, but it is the most important component of your wall. By using a code-compliant two-layer system (like Super Jumbo Tex 60 Minute), Stucco Champions ensures your home remains dry and structurally sound for generations.
Last week, we shared Grade D Building Paper: Code Requirements and Benefits. Dive deeper into the specific ASTM standards for paper selection.
Need stucco repair in Southern California? Stucco Champions proudly serves homeowners throughout Orange County, Los Angeles, Riverside, and San Bernardino counties. Check out our Service Areas page to see all the cities we cover.