You may have heard this term and thought, what exactly is that? No, it isn’t a fancy term for an umbrella or something you plant bougainvillea on. It’s not an object at all. It’s actually a construction technique. A rain screen is very similar to a “cavity wall”. If your house has brick veneer on the exterior then it is a cavity wall. Here’s what a cavity wall consists of:
- Layer 1: This is the first line of defense against moisture intrusion. Inevitably some amount of moisture is absorbed or pushed through the brick.
- Layer 2: An air “cavity” that allows moisture to escape.
- Layer 3: The structural system which has a weatherproof barrier that creates a drainage plane, keeping moisture from penetrating your house.
So what is the difference between a “cavity wall” and a “rain screen wall”? The only significant difference is that outer layer. In a cavity wall the outer layer is installed like a shield to keep out as much water as possible. The “cavity” or airspace behind is simply secondary defense to get rid of what the first layer couldn’t keep out. What the rain screen wall does is treat the outer layer as a “screen” more so than a shield. It’s installed to intentionally allow some moisture past the first layer to the weatherproof barrier behind it. As you can see in the image above the wood siding is installed with gaps between each board, so while much of the moisture will be “screened”, some will get behind it.
And what advantages does the rain screen offer? It’s an “open” system so it allows for increased and continuous ventilation of the wall. In other words the wall system is constantly being hung out to dry rather than being wadded up in a wet ball on the floor. You also get decreased maintenance, particularly in wood siding applications and reduced mold and mildew issues. The cladding can be made from almost anything as long as it is durable, including masonry, metal, glass and even fabric.
If you’re thinking of incorporating this into your project talk to your contractor and take a look at this concealed clip system that eliminates exposed nails or screws.
Image: Fine Homebuilding 137, pp. 86-91
