While we all want a home that is comfortable and beautiful, we also want a solid structure made of durable materials that will last for years to come. But the durability of our homes is threatened by environmental factors, especially wind, rain, heat, and humidity. Incorporating a high-performance rainscreen system will help protect your home from the damaging effects of moisture.
What is a rainscreen?
A rainscreen is not actually an individual product, but part of a wall construction system. Its overall purpose is to protect the wall sheathing from moisture that gets past the siding. Rainscreen systems typically consist of the following components:
- Exterior cladding (siding)
- Ventilation and drainage cavity
- House wrap (drainage-plane material)
- Air barrier
Perhaps the most important component is the ventilation and drainage cavity which provides space between the siding and the house wrap. This space is typically created by applying vertical furring strips (called strapping) over the drainage-plane material. The siding is then nailed to these wood strips.
Newer rainscreen products, such as Slicker, achieve the same effect by using a three-dimensional matrix with vertical channels. These products come in a roll and are laid over the entire surface of the wall, providing a continuous space for drainage and drying. When compared to a product like Slicker, wood strapping is generally less expensive from a material cost but is more expensive to install from a labor standpoint. Other drawbacks of strapping include the creation of hot spots along studs and trapped moisture from wood-to-wood contact, which can lead to reduced air movement and a greater potential for mold.
Why would you want a rainscreen?
A rainscreen is important because the ventilation cavity promotes residual water drainage and airflow. Any moisture held in the siding, or that seeps underneath due to wind-driven rain, will diffuse and evaporate. If there are ventilation openings at the top (as opposed to only a weep holes at the bottom), the rainscreen provides a path for rising air. According to homebuilder Martin Holladay, research shows that this type of ventilation is a powerful drying mechanism. Because airflow is promoted, rainscreens have the added benefit of keeping your siding cool which prevents premature failure.
Homebuilder Mark Averill Snyde suggests the airspace provided by a ventilation cavity is especially important to prevent “capillary action.” He compares this process to a grade-school science experiment during which a stalk of celery is placed into a glass of colored water and the water is observed to move quickly upwards. The same thing can happen to homes without proper ventilation and house wrapping.
Isn’t house wrap sufficient?
Some builders and homeowners believe house wrap (such as Tyvek, Typar, and #15 or #30 felt) provides a sufficient barrier. But for many homes, especially those in wetter climates, it’s not enough. The primary function of house wrap is to drain water that penetrates the siding through leaky joints or capillary action. However, house wraps lose their water repellency over time and do very little to reduce air infiltration due to heavy winds. Once water penetrates the house wrap into a wall, peeling paint and rotten siding often follow. According to Joseph Lstiburekis from Building Science Corporation, back-priming wood cladding and trim and adding a ventilation cavity reduce the impact of moisture.
In addition to a rainscreen system, other methods to protect your home from water damage include:
- high-quality gutters (that are regularly cleaned)
- properly sealed windows and doors
- wide roof overhangs
- flashing around external wall penetrations (such as cable service entrances or ventilation system intake and exhaust hoods)
While a rainscreen system is important for most homes, it is especially vital in climates that are wet and hot. Some experts advise rainscreen installations for all houses in areas with an average annual rainfall of 50 inches or more. Many coastal areas get that much rain each year, so if you’re planning to build a beach home make sure you discuss rainscreens with your contractor.
Blog by Jessica T. Smith for the Coastal Cottage Company