The building envelope is the most critical line of defense against moisture intrusion, and housewrap has been a standard component of that defense for decades. Traditional housewraps work by allowing water vapor to pass through while shedding liquid water, a compromise that has served the industry well but is not without limitations. Delta-Dry, manufactured by Cosella-Dörken Products, takes a fundamentally different approach: instead of relying on permeability to manage moisture, it creates a drained and ventilated cavity on both sides of the membrane, providing a continuous rain-screen effect without the added cost and complexity of a separate rainscreen assembly.
How Delta-Dry Works
Delta-Dry is a semirigid plastic membrane approximately 1/4 inch thick, embossed with a pattern of dimples and channels across its entire surface. When installed against the sheathing, the dimples create a continuous air gap between the membrane and the sheathing. A second air gap exists between the membrane and the exterior siding. Both gaps allow air to circulate freely, carrying away moisture that would otherwise remain trapped within the wall assembly.
The dimpled geometry serves a dual purpose. First, it creates a capillary break: any liquid water that penetrates the siding cannot bridge the gap to reach the sheathing. Second, the channels provide a drainage path: water that condenses on the interior face of the siding or the exterior face of the sheathing runs down the channels and exits at the bottom of the wall, above the foundation.
This design represents a departure from the conventional wisdom that a housewrap must be permeable to function correctly. Rather than relying on vapor diffusion through the material, Delta-Dry manages moisture through ventilation and drainage, which are orders of magnitude more effective at removing bulk water than diffusion alone.
Installation Guidelines
Delta-Dry is supplied in rolls 39 inches wide and 50 feet long, and it can be cut to length with a standard utility knife. The material is installed directly over plywood or OSB sheathing, overlapping seams by 6 to 8 inches just like traditional housewraps. Fastening is done with 1/2-inch roofing nails or 3/4-inch staples driven with a pneumatic stapler. A hand stapler will not provide sufficient holding power, regardless of how many staples are used, because the semirigid plastic resists penetration and requires more force to seat the fastener properly.
Window and door openings are detailed using peel-and-stick flashing tape applied directly over the Delta-Dry membrane. The flashing should extend at least 6 inches onto the field of the membrane and be pressed firmly into the dimples to create a continuous seal. At the bottom of the wall, a drip edge or weeper system should be installed to allow accumulated moisture to exit while preventing insects and debris from entering the cavity.
The product is compatible with a wide range of exterior claddings, including brick, stucco, wood clapboards, vinyl siding, and shingles. For brick veneer, the Delta-Dry dimples provide a continuous air gap that meets the 1-inch minimum clearance typically required by building codes behind brick. For stucco applications, the membrane serves as both the weather-resistant barrier and the drainage plane, eliminating the need for a separate building paper layer.
Advantages Over Conventional Housewraps
The primary advantage of Delta-Dry is that it combines the functions of a weather-resistant barrier and a rain screen into a single product. Conventional housewraps require a separate rainscreen assembly—typically furring strips or a drainage mat—to create the ventilation cavity behind the siding. This adds material cost, labor time, and complexity to the wall assembly. Delta-Dry eliminates the need for these additional components, simplifying the installation while improving performance.
In terms of moisture management, the ventilated cavity approach is far more robust than relying on vapor permeability alone. Even the most permeable housewraps have limited drying capacity, especially when faced with bulk water intrusion from wind-driven rain or failed siding. Delta-Dry’s drainage and ventilation system can handle bulk water volumes that would overwhelm a conventional housewrap, making it particularly well-suited for buildings in high-rainfall or coastal environments.
For builders interested in learning more about building envelope strategies, understanding modern housewrap systems provides a useful baseline for comparing different products and approaches. The choice of housewrap interacts with other components of the wall assembly, including building insulation methods, and the best results come from designing the wall as a integrated system rather than a collection of independent layers. Proper integration with exterior wall cladding options ensures that the drainage cavity functions as intended. Finally, for those dealing with moisture issues in existing construction, the principles behind Delta-Dry also apply to water penetration prevention in masonry walls.
Limitations
Delta-Dry is not an air barrier. While it provides excellent moisture management, it does not reduce air leakage through the building envelope. For projects that require an air barrier—increasingly common in energy-efficient construction—separate air-sealing measures must be implemented. This can be done by taping all sheathing seams and penetrations at the interior side, using an air-sealant system at the exterior, or installing a dedicated air-barrier membrane in conjunction with Delta-Dry.
The product is also more expensive than standard housewraps, costing approximately $0.80 to $1.20 per square foot compared to $0.10 to $0.30 for polyethylene-based wraps. However, when the cost of a separate rainscreen assembly is factored in, the total installed cost of a Delta-Dry wall is often comparable to or lower than that of a conventional housewrap-plus-rainscreen assembly.
Conclusion
Delta-Dry represents a significant step forward in weather-resistant barrier technology. By replacing the permeability paradigm with a ventilation-and-drainage model, it delivers superior moisture management in a single, easy-to-install product. For builders in wet climates, coastal regions, or any project where moisture durability is a priority, Delta-Dry offers a proven solution that simplifies the wall assembly while improving long-term performance.