Rainscreen Design for Solar Driven Moisture

The famous architect Louis Kahn was on to something big when he said, “The sun never knew how great it was until it hit the side of a building.” Once the plans have been envisioned, drafted, approved and finally realized, an architects best friend or worst enemy is the sun, especially when it comes to moisture! This is one lesson better learned before breaking ground on even the most innovative of commercial architectural feats: make the sun your best friend with smart engineered rainscreen design.

Solar driven moisture can penetrate many building materials and accelerate growth of mold causing materials to decay.   However, the materials of the greatest concern are highly absorptive claddings (also known as reservoir claddings) such as conventional stucco, manufactured stone veneer, and cementicious siding. Solar driven moisture occurs when water that has soaked into the cladding is forced further into the wall by the heat of the sun. The wall looks like it dries to the outside, but it doesn’t. Green Building Advisor Martin Holladay provides more detail about solar driven moisture in this article

“But don’t I have a WRB in the wall? Won’t that protect my building?” one may ask. The answer is that the WRB won’t protect you from solar-driven moisture at all. The WRB is moisture-vapor permeable. And the thing about anything that is moisture-vapor permeable is that it is permeable both ways. A membrane that is permeable only one way does not exist. This means that, without any protection, moisture that the sun drives in can be driven all the way into the wall. When moisture gets to the cooler air-conditioned interior, you risk condensation in the wall cavity. Moisture in the wall cavity can have huge repercussions for the durability and life span of the building.

Solar driven moisture can be managed with the use of drained and back-ventilated engineered rainscreens. This will allow the majority of water that penetrates the cladding to drain efficiently and through strategically designed openings at the bottom of the wall, minimizing moisture accumulation.   Because the rainscreen is open at both the top of the wall as well as the bottom, any accumulated moisture can be ventilated quickly before it can contribute to rot and mold growth. This “bonus” drying energy comes from the buoyancy of air through the space as the wall is heated by the sun (hot air rises!) and through air pressure differential as the wind blows against the structure.

There are several types of engineered rainscreens available today (for more information on engineered rainscreens click here). The more familiar may be the open entangled meshes. Another is the solid-faced dual-chamber dimpled version. Each will give you drainage, ventilation and a capillary break. Only the dimple version gives you the full barrier that adds the protection from solar-driven moisture (for more information, click here).

Make the sun your best friend, not your worst enemy in commercial and residential architecture. Our engineered rainscreen designs meet commercial specifications for drainage, ventilation, durability and reliability.