Exterior Wall Cladding, What is exterior wall cladding

Exterior wall cladding speaks to what is exterior wall cladding and types of exterior wall cladding.

It is rain screen cladding and the generic solution to wind current problem which is to allow wind pressure differences between the outside and inside of the exterior wall to neutralize themselves through a concept known as pressure equalized wall design.

This involves the creation of an airtight plane, known as the air barrier, behind the outer face of the wall. The air barrier is protected from direct exposure to the outdoors by an unsealed, labrynth jointed layer known as the windscreen. Between the rainscreen and the barrier is a space known as the pressure equalization chamber (PEC).

As wind pressures on the exterior wall build up and fluctuate, small current of air pass back and forth through each unsealed joint in the rainscreen, just enough to equalize the pressure inside the PEC with the pressure immediately outside of it.

These currents are far too weak to carry water with them. A small flaw in the air barrier, such as a sealant bead that has pulled away from one side of the joint, is unlikely to cause a water leak because the volume of air that can pass through the flaw is still relatively small and is probably insufficient to carry water.

By contrast any flaw, no matter how small, in an external sealant joint without an air barrier behind it will cause a water leak, because the sealant joint itself is wet.

Because wind pressures across the face of a building may vary considerably at any given between one area of the face and another, the PEC must be divided into airtight compartments small enough so that volumes of air cannot rush through the joints in higher pressure areas of the face and flow across the air chamber to lower pressure areas, carrying water with them.

The appropriate size of these chambers may vary considerably, depending on the design of the wall system and the wind forces to which it is exposed. Broadly speaking, PECs are normally no taller than one story or wider than one or two columns bay. In some applications they may be significantly smaller.

The term rainscreen principal originated with the concept of pressure equalized wall design and at one time it was used exclusively in reference to pressure equalized cladding systems. More recently the term rainscreen cladding has become to be applied more broadly to any cladding system with a system of internal drainage, regardless of the extent of compartmentalization of the drainage space and the degree of pressure equalization that can be achieved.

In practice, varying degrees of pressure equalization are achievable and the line between cladding systems best characterized as simple rainscreens or pressure equalized walls is often the same.

 

 

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