Let’s quickly revisit what moisture-related wall damage looks like:
Before I get into the details of a rainscreen, I want to mention a few misconceptions about moisture in exterior walls:
False: Moisture and water problems only happen in basements that are below-grade.
Actually, moisture problems in walls above-grade are most common in the hot and humid southern United States, but there is a substantial amount of moisture-related wall failure right here in the Chicagoland area. In our area, we have the hot, humid summers, but we also have the extreme winters that produce a considerable amount of freeze-thaw cycles, and this can be a big problem for wall moisture.
False: My siding, brick or stucco cladding keeps all water and moisture out the wall.
Exterior cladding does protect the inner wall to a degree, but none of these materials fully keep water out of a wall assembly. Brick and stucco are very porous; moisture vapor and “bulk water” (water you can see) will pass through. Siding is typically designed to shed the water but it also relies on sealants that are not permanent (they do crack and fail). As a rule of thumb, when a wall is designed and constructed, it should be done in a way that deals with moisture that gets past the exterior cladding. Be sure to find a reliable Siding Contractor Atlanta in order to protect your home from water damage.
False: Moisture always comes from the outside and works its way to the inside.
In general, air moves from warm to cool, carrying moisture with it. In a hot climate, moist air moves from the hot exterior of the home to the cool, dry interior. In a cold climate, moist air moves from the warm interior to the cold exterior. Because of this law, moisture is constantly passing through an exterior wall assembly. Moisture is constantly passing through the building envelope; the moisture source can come from the interior as well as the exterior. The takeaway here is that you do not need a leak to have a mould or deterioration problem in your walls.
With the understanding of the principles above, you can now see that there is some science involved: a wall assembly needs to be designed and installed properly. Although there are no “one size fits all” wall designs, the basic consistency is that a wall needs to be able to prevent moisture buildup. This is where a rainscreen comes into play.
FYI, most climates in the United States experience extreme weather. In addition to moisture, the Building Science Corporation says rainscreens must also resist wind, snow, solar radiation, impact, flame spread, etc.
Do not get confused by the name “rainscreen.”
When I think of a window or door screen, I think of an item put in place to keep things (bugs) out. A rainscreen in wall construction does not typically keep anything out; it is actually an infrastructure used to create an air gap between the building wrap and the exterior cladding. Just think of this as a pathway for air movement; that is what a rainscreen basically is.
Rainscreens are a support mechanism.
A rainscreen does NOT replace your building wrap. They should be constructed in addition to – NOT in replacement of – house wrap. When installed properly, rainscreens help dry up any moisture that accumulates on the building wrap.If you haven’t done so already, please take a brief moment to read my blog about house wrap where I covered the 4Ds of a quality house wrap (deflect, drain, dry and provide durability).
Read about the history of rainscreen wall construction, which dates back to medieval Norway.
Now let’s take a look at a few of the ways to create this infrastructure using some of the more common products available. I will break my examples into three product categories and provide some examples of which cladding materials they are used with (in no particular order of importance):
Option 1: Open joint siding wall assembly using a furring strip-style rainscreen:
Pictured above: Wood Haven, Inc.’s Rainscreen Clip™ system can be installed vertically or horizontally. It is a kit including specially milled lumber (wood siding), matching trim and corner boards, and pre-drilled, rot-resistant furring boards for accurate installation, in addition to painted marine-grade aluminum hidden fasteners, starter clips and screws. I should also note that this is an “open joint” siding style that many architects will specify. This simply means that there is a small space between each piece of siding.
When using an open joint siding, it is CRITICAL to use a UV-rated WRB like the high-quality Delta FS that will not break down or deteriorate with sun exposure over time. The mistake of using a non-UV-rated building wrap will eventually result in wall failure. You can check out the Delta®-Fassade S brochure here.
Option 2: Closed joint wood and cement board siding wall assembly:
Many companies now make furring strip-type rainscreen kits that are an alternative to wood strips. They can be used with closed joint wood and cement board siding products, and they include everything needed to complete the installation, including bug screens and window flashings. DuPont is one of many companies that offer this complete system, such as the DuPont™ RainVent™ Batten kit.
Benjamin Obdyke is one of many companies that manufacture a rainscreen mesh that gets rolled onto a wall prior to the cladding installation. This mesh creates a 6mm pathway for air to circulate so the drainage plane can dry better. Read more about the Benjamin Obdyke Home Slicker® 6mm Rainscreen here.
Option 3: Solar-driven moisture: A unique challenge that requires a very specific wall design
So far I have shown some good options for creating a rainscreen for siding. Benjamin Obdkye suggests that its product is made to work with EFIS (Exterior Insulation and Finish Systems)to prevent the terrible problems the industry has seen with EFIS installations. Now I would like to provide some wall assembly solutions for dealing with solar-driven moisture. If you have not heard of this before, you are not alone.
Unfortunately, most stucco installers, masons and general contractors just do not concern themselves with the information that is out there. For a more detailed explanation of a study that was done on this topic, read this recap from the 2010 International Conference on Building Envelope Systems and Technologies.
Because all brick, stone and stucco is porous, it can store a substantial amount of moisture. When this material is installed directly to a wall assembly, the stored vapor can be driven inward on a hot day during or after a rain. Remember: warm, moist air will be driven inward and all the moisture stored in the cement, brick, mortar, etc. will be driven directly into the wall cavity because the building wrap is permeable by design. The next wall assembly details will combat solar-driven moisture in addition to creating a rainscreen infrastructure.
Pictured above: The Delta®-Dry ventilated rainscreen is made by Cosella-Dörken. The structured membrane provides drainage and ventilation, as well as a complete capillary break behind the cladding. It protects the building envelope from bulk water intrusion (i.e. wind-driven rain and solar-driven moisture), and manages water leakage through the cladding. As well, Delta-Dry captures and drains transient moisture migrating through the wall structure; it provides an air-gap on the interior and exterior side of the membrane for drainage and ventilation.
Of all the rainscreen products available, I really like the Delta products by Cosella-Dorken because I trust them the most. The dimple design of Delta-Dry will never compress like a mesh, and the air flow is increased as a result. This is the only solution I am aware of that combatssolar-driven moisture. I also appreciate the design flexibility provided by Delta. It offers multiple products that I can pick and choose from based on the goal of the design for each wall assembly.
So with all the benefits of a rainscreen, why do so FEW homes in the Chicagoland area include this great technology?
I have never taken a formal survey, but my guess would be that there are two main reasons why rainscreens are not used more in the Chicagoland home market.
- The first is that many general contractors and tradesmen are just not aware that they exist.
- The second is that these types of wall construction involve an extra step and additional cost.
I have worked with many masons and stucco contractors over my 25 years as a building and remodeling contractor. I have yet to find one that suggests using a product to combat solar-driven moisture. In most cases, they do not want to do anything that will increase their price, because most builders are looking for the bottom-line lowest cost. Sad but very true. I personally believe that wall assembly construction is an area where you should NOT take shortcuts because you can’t add this on later. I think architect Bud Dietrich, AIA agrees with me on this one.
Bud is licensed to practice architecture in Illinois, Florida, New Jersey and Wisconsin. In his article titled “Architect’s Toolbox: Rainscreens Up House Health” on Houzz.com, he says that rainscreens can be installed with just about any type of exterior finish material and just about any style, and well worth the cost in order to keep moisture out of your home!
My Invitation to you
Whether you are a homeowner considering a project or an architect who designs homes from Barrington to Burr Ridge, I would like to talk to you about our experience with rainscreen technology and invite you to come see us install this at our 2014 Project Spotlight between August 15 – September 15, 2014. Call me to set up a time to visit in person.
I would like to show you first-hand how I am committed to using techniques that support “building for longevity”: homes that last and are structurally sound for more than 100 years! The running theme here is that a properly designed and expertly installed rainscreen system provides moisture management and energy efficiency. If you don’t incorporate rainscreen technology into your new construction or remodeling project, you run the potential risk of costly water damage down the road resulting in mold, mildew and rot in your structural walls.