This is NOT a true rainscreen.
Rainscreen Technology
What is a Rainscreen?
- A rainscreen is the exterior weather facing surface of an exterior wall detail that stands off from the moisture resistant surface of the structural back up wall.
- In many cases this would be a brick veneer, stone veneer or other types of masonry veneers.
- The rainscreen is the first first line of defense against the effects of moisture on the wall detail.
- A rainscreen also helps protect the interior of the wall detail from a variation in air pressure (wind), ultraviolet rays of the sun and other severe weather conditions.
- A rainscreen is the exterior portion of the cavity detail.
A very important, though often ignored, point about rainscreens:
***A veneer that does not stand off from the moisture resistant surface of the structural backupwall to create a cavity is NOT a true rainscreen, it is just a veneer.
What Must Rainscreen Technology Really Do?
1. It Must Be A Predictable Drainage Plane
- It must create a separation between the backside of a masonry veneer and the exterior surface of the moisture resistant construction paper on the exterior sheathing of the structural back up wall.
- This allows moisture in a liquid state (water) that passes through the rainscreen to have an unobstructed path from a high point of the wall, where it enters, to a low point of the wall, where it exits.
- Water must exit a wall system quickly. It is all about the amount of time that water is in a wall detail and how much it absorbs into the interior materials of a wall detail.
2. It Must Be A Predictable Pressure Equalization Plane
- It must create a separation between the backside of a masonry veneer and the exterior surface of the moisture resistant construction paper that is installed on the exterior sheeting of the structural back up wall.
- This allows moisture contaminated air to exit the interior of the wall system from all points in that wall system.
- Moisture laden air that is allowed to pressurize will attempt to move to a lower pressure, which may be deeper into the interior of a wall detail.
When air moves from a location of high pressure to another location of low pressure, there is air flow. This phenomenon could occur across thousands of miles or a fraction of an inch. The volume of air could be a hurricane or the slightest draft.
The amount of moisture a hurricane can move in its air flow is billions of gallons. The amount of moisture a slight draft can move is less.
Once moisture has penetrated deep into a wall system (through the moisture resistant construction paper and into the exterior sheathing) the wall is deep wet. The air flow that exists in most wall systems is a slight draft that will not dry this condition out quickly. (The wall is in serious trouble!)
Learn more about the "Time factor" in moisture control through MTI's About Time research video.
