Rainscreens: Let It Rain!


Sustainability, or "green" building, is something that is becoming more and more common these days, and in some respects expected by new home buyers. In fact, green codes and regulations are now codified and part of the California Building Code (CBC). More specifically, Chapter 11 of the CBC covers "green" building and is typically referred to as CALGreen.

At The 4Corners Group, we have incorporated sustainable design as our standard and default building method.

Providing homes that are comfortable, have excellent indoor air quality, and don't leak is huge for us. On our Preuss project, we decided to incorporate a rainscreen system for our exterior siding. Rainscreens, as the name implies, act as a screen on the home and are used to prevent rainwater penetration through the exterior walls. In some areas of the country they've been using them for decades, Seattle for example. In L.A. you see it every now and then, but its not what I would call a common siding method here due to its increased cost. The idea is a simple one really, but in order to understand why rainscreens work its import to understand one of the primary ways in which water gets into a home in the first place: capillary action.

Capillary Action:

Without getting too much into the weeds, capillary action is a suction force between two surfaces, that in buildings, can draw water into permeable materials and small openings. So, when it rains, rainwater can and sometimes does, find its way behind the exterior material of a home, let's say stucco. Once inside the building envelope it finds it has no where to go, so it just sits there. This is where capillary action comes in. Because of unequal pressure between the inside of the house and the outside of house, one side "sucks" the trapped water towards it. In many cases, the inside of the house sucks the water in and before you know it, you've got a problem.

Rain screens simplified:

A rain screen system helps prevent moisture from getting into the home in two ways: first, it repels most of the rainwater hitting its surface just like any other system, second, it allows water that gets behind it to easily escape and or evaporate. It can do this because the siding material sits away from the actual waterproofing material. This air gap is what allows water to escape, and it also allows for air flow which helps any remaining water to evaporate. The air gap also adds an intermediate pressure zone that helps deal with the unequal pressures between the inside and outside and therefore reduces capillary action.

Rainscreens definitely cost more to do than let's say stucco. However, we feel the additional cost is worth it since it helps prevent one of the most common deficiencies in home building, leaks. Its just another way we can let our owners concentrate on living simply!

For a more detailed explanation on rainscreens, see this article in Architect magazine or this website.

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