Modern wall systems are designed to manage both air and moisture, making house wrap performance more important than ever. For years, breathability has been a major focus in house wrap design because it allows water vapor to escape from wall assemblies. While vapor permeability is important, breathability alone does not fully address one of the biggest challenges in exterior wall systems: liquid water that becomes trapped behind the cladding.
The Difference Between Vapor and Bulk Water
Breathable house wraps are designed to allow water vapor to pass through the material while resisting liquid water penetration from the outside. This helps wall systems dry over time and reduces the risk of moisture accumulation caused by vapor diffusion. However, water vapor and bulk water behave differently inside a wall assembly. Once liquid water gets behind the siding, it needs a path to drain away from the structure.
Why Water Gets Behind Cladding
Exterior cladding systems are not completely waterproof. Wind-driven rain, penetrations, flashing transitions, and small installation gaps can all allow moisture to move behind siding. Even properly installed exterior systems are designed with the understanding that some water intrusion will occur. The goal is not simply to block all moisture, but to manage it effectively once it enters the assembly.
The Limitation of Flat House Wraps
Traditional flat house wraps rely heavily on breathability while remaining compressed directly against the wall surface. Without a defined drainage space, water that reaches the wrap can become trapped between the cladding and the wall assembly. In these conditions, drying may occur slowly, especially in humid climates or areas with limited airflow behind the siding.
Why Drainage Matters
A drainage space creates a path for liquid water to move downward and exit the wall system. This separation reduces prolonged moisture contact and helps improve drying performance behind the cladding. Effective moisture management depends not only on permeability, but also on the ability to physically move water away from the structure.
Combining Breathability with Drainage
Modern drainable house wraps are designed to address both vapor movement and bulk water management. By incorporating a structured layer into the wrap, these systems create consistent drainage channels that allow water to escape while still supporting vapor permeability. This approach improves moisture management without sacrificing breathability.
How Material Structure Improves Performance
Products like ALTA® 360 use a structured reinforcement layer to create drainage pathways behind the cladding. Unlike embossed or textured surfaces that may compress under pressure, structured drainage layers maintain separation across the wall surface, helping water move downward and out of the assembly. This combination of breathability and drainage supports more effective long-term wall performance.
Building Smarter Wall Systems
As building envelopes become tighter and more energy efficient, moisture management becomes increasingly important. Breathability remains a key component of wall design, but it is only part of the solution. Managing the liquid water that inevitably reaches the wall assembly requires drainage as well. House wrap systems that combine both functions help support more durable, resilient wall assemblies over time.