House wrap plays an important role in protecting buildings from moisture, but not all weather-resistive barriers (WRBs) manage water in the same way. While traditional house wraps provide a water-resistive layer behind exterior cladding, drainable house wraps incorporate additional features designed to help incidental water move downward and out of the wall assembly.
As building envelope designs evolve, understanding the differences between these materials can help builders, contractors, and architects make more informed decisions about moisture management and long-term building performance.
What Is Traditional House Wrap?
Traditional house wrap is a weather-resistive barrier installed over exterior sheathing and behind the cladding. Its primary function is to resist liquid water that penetrates the exterior finish while directing that moisture toward flashing and designated drainage exits.
Many traditional house wraps are also vapor permeable, allowing moisture vapor to diffuse through the material under appropriate conditions. This helps support drying potential within the wall assembly.
However, because conventional house wraps typically have relatively flat surfaces, their drainage performance can depend heavily on the surrounding wall design. When exterior cladding is installed directly against the WRB, the limited separation between materials may restrict how easily water moves through the assembly.
What Makes Drainable House Wrap Different?
Drainable house wraps are designed to provide an additional pathway for water movement behind exterior cladding. Rather than relying solely on the surface of the WRB, these products incorporate textured surfaces, raised patterns, or integrated drainage structures that help create separation between the cladding and the underlying water-resistive layer.
This separation provides channels through which incidental water can move downward under gravity and reach designated drainage exits.
The design is particularly useful in wall assemblies where exterior cladding may retain moisture or where limited separation between materials could otherwise restrict drainage.
Why Drainage Matters Behind Exterior Cladding
Exterior cladding is the first line of defense against rain, but it is not necessarily a completely watertight surface. Wind-driven rain, joints, fasteners, and material transitions can allow moisture to reach the space behind siding, brick, stone, or other exterior finishes.
When water reaches the WRB, it needs a reliable path out of the wall assembly. Without adequate drainage, moisture may remain in prolonged contact with surrounding materials, increasing the potential for moisture accumulation.
Drainable WRBs help address this challenge by providing a more defined pathway for water movement. When properly integrated with flashing and drainage exits, these systems can help reduce the amount of time incidental moisture remains within the assembly.
Drainable vs. Traditional House Wrap: Key Differences
Both traditional and drainable house wraps serve as weather-resistive barriers, but their designs can influence how they manage water.
| Performance factor | Traditional house wrap | Drainable house wrap |
|---|---|---|
| Water resistance | Resists liquid water | Resists liquid water |
| Drainage | Depends on wall assembly and detailing | Incorporates drainage features |
| Vapor permeability | Varies by product | Varies by product |
| Separation behind cladding | Often limited without additional components | Designed to provide drainage pathways |
| Installation | Requires proper overlaps and flashing | Requires proper overlaps, flashing, and drainage detailing |
| Moisture management | Provides a water control layer | Combines water control with integrated drainage functionality |
Neither approach eliminates the need for proper wall design. Traditional house wraps can perform effectively when incorporated into well-designed drainage assemblies, while drainable house wraps offer an additional material option where integrated drainage is desirable.
How Drainage and Vapor Permeability Work Together
Drainage and vapor permeability address two different forms of moisture movement.
Drainage manages liquid water that enters behind the cladding, allowing it to move downward and exit the wall assembly. Vapor permeability, on the other hand, describes how readily water vapor can diffuse through a material.
A drainable WRB that is also vapor permeable can support both functions, helping manage incidental liquid water while allowing vapor diffusion under suitable conditions.
However, the overall drying potential of a wall depends on more than the WRB alone. Climate, insulation placement, interior vapor control, exterior cladding, and other components all influence how moisture moves through the assembly.
Where ALTA® 360 Fits
ALTA® 360 is engineered as a drainable, vapor-permeable weather-resistive barrier designed to support moisture management behind exterior cladding.
Its two-layer construction combines an outer film with CLAF® reinforcement. The CLAF reinforcement provides the integrated drainage technology, helping establish pathways for incidental water to move downward through the wall assembly.
This construction allows ALTA 360 to combine water resistance, vapor permeability, and drainage functionality within a single engineered product.
For builders and specifiers evaluating house wrap options, ALTA 360 offers an alternative to conventional flat WRBs when integrated drainage is an important consideration.
As with any weather-resistive barrier, proper installation and integration with flashing, penetrations, and surrounding building components are essential for achieving the intended performance.
Choosing the Right House Wrap for Your Project
The decision between traditional and drainable house wrap should begin with the needs of the building rather than a single product characteristic.
Builders should consider the type of exterior cladding, local climate, exposure to wind-driven rain, wall assembly design, and applicable building requirements. They should also evaluate documented product performance and compatibility with the other materials used throughout the building envelope.
In some assemblies, traditional house wrap combined with appropriate detailing and separate drainage components may provide an effective solution. In others, an integrated drainable WRB may offer a practical approach to creating a defined drainage pathway.
The goal is not simply to select a product that resists water, but to design a complete wall assembly that manages moisture effectively.
Looking Ahead
Understanding the differences between traditional and drainable house wraps is an important step toward making informed building envelope decisions.
Throughout our Building Envelope Basics series, we’ve explored the roles of water, air, vapor, and thermal control layers, the importance of flashing and continuity, common installation challenges, and the characteristics to consider when choosing a WRB.
In Part 10, we’ll bring everything together with Designing a High-Performing Building Envelope: How the Control Layers Work Together, exploring how these individual components contribute to a complete building system.