Wall Pressurization, What is wall pressurization

Wall pressurization speaks to what is wall pressurization, why wall pressurization , types of wall pressurization.

It is known as pressure equalized wall design. This is a cladding design that embodies the rainscreen and pressure equalization principles, in very simple form.

No surface joint sealants or gaskets are used. The metal rainscreen panels do not touch one another, but are separated by generous gaps that preclude capillary movement of water, provide installation clearances and allow for expansion and contraction. All four edges of each panel are shaped so as to create labrynth joints and the forces of surface tension and gravity are counteracted by sloping surfaces and drips.

Installation is simple and forgiving of minor lapses in workmanship. Metal U shaped clips are bolted to the backup wall, which is coated with an airtight mastic to create an air barrier. Rigid insulation panels are adhered to the wall, allowing the clips to project through.

Finally the metal panels that make up the the rainscreen are simply hung on horizontal rods that are supported by the channels, much as pictures are hung on hooks on a wall. The space between the metal rainscreen panels and the insulation acts as an internal drainage space.

To achieve a pressure equalized design, horizontal metal angles are installed between the channels at one or two story intervals. The vertical channels further divide the PEC into narrow compartments. The spaces between the edges of the panels and the channels are narrow enough to restrict air flow sufficiently to achieve a pressure design.

If more complete compartmentalization is needed, compressible foam rods or gaskets can be installed alongside the channels to create more airtight boundaries at these locations. When wind drives rain against this wall, small quantities of air flow through the open joints in the rainscreen until the pressure in the PEC equals the outside pressure. These air flows are sufficient in volume or velocity to carry water with them.

The principals of rainscreen design and pressure equalization may also be applied on a small scale to guide us in many aspects of exterior detailing of buildings. This practice may be embodied in the placement of weatherstrip in a window sill detail.

In the correct detail, the weatherstrip, whose function is to act as an air barrier, is placed to the inside of the lower rail of the sash. The open joint under the sash rail, which is provided with a capillary break, acts as the PEC. Unless the weatherstrip is grossly defective, water cannot be blown through the joint by air pressure differentials.

Notice how the other forces that could transport water through the joint are counteracted. A slope on the sill called a wash, prevents gravity from pulling water in. The groove in the lower edge of the sash that acts as a capillary break also acts as a drip to counteract surface tension. The L shaped joint between the sash and the sill acts as a labrynth to prevent entry by momentum.

In an incorrect installation, the weatherstrip can be wetted by rain. Any minor flaw in the weatherstrip will allow water to be blown through the joint.

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