This is the most advanced method of rain penetration control.  When applied correctly, it limits direct entry, it prevents capillary action, it manages cavity drainage correctly and it arrests the penetration of wind driven rain. To do so, a rainscreen application involves more than a specialized cladding.  Specifically, a rainscreen system must include a drained and vented cladding, a cavity behind the cladding, an air barrier system in the backup wall, compartment seals in the cavity and suitable flashings for drainage from the cavity.

When a rainscreen cladding and wall system functions correctly, it controls wind driven rain by separating the rain from the wind pressure and dealing with them separately.  As the wind impinges on the cladding, it penetrates into the wall cavity through cladding vents to push on the backup wall air barrier system.  If the air barrier is tight and well supported, the wind stagnates in the cavity to increase the cavity pressure until it rises to become about equal to the surface pressure on the cladding.  When these two pressures become roughly equal, the rain is no longer pushed or entrained into the wall cavity.   The rain then flows downward over the surface of the cladding to be rejected at the next flashing, drip or cut.  It is in this manner that the rainscreen separates the rain from the wind.  The rain is effectively stopped at the cladding surface  while the wind is effectively resisted by the backup wall and air barrier system.

In addition to the above, the rainscreen system must also prevent the wind cavity pressure from spilling around the corner or over the roof if the cavity pressure is to be equalized with the wind pressure during a storm.  It is for this reason that the cavities of a rainscreen system are compartmentalized at or near the roof line and at or near building corners.  In addition, the compartment seals must be robust and strong to resist differences in pressure from one cavity to the other.  

Once again, a rainscreen system is not a cladding material.  It does not function unless the backup wall includes an effective air barrier, the wall cavity includes compartment seals and the system is equipped with suitable drains and cladding vents to allow wind pressure equalization.  Also, should a leak occur through the exterior wall it may be necessary to dismantle part of the cladding to make corrections or repairs, The rainscreen system cannot be repaired by the application of caulking to the outside.  

Alternately, the addition of wall cavities, vents and drains and air barriers, can significantly reduce heating and cooling energy losses, minimized condensation problems in summer and winter, minimize or eliminate the production of mold and reduce cladding maintenance to practically zero.

The rainscreen principle has been successfully applied to numerous types of cladding to include aluminum curtain walls, various precast wall systems. steel buildings, masonry walls and window designs.  The application of the rainscreen principle provides the best overall rain penetration resistance in comparison to other methods.

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