But Secure? As vital parts of the exterior enclosure of buildings, windows must resist weather conditions while helping to maintain a comfortable interior space. They must withstand wind, rain, projectiles and exterior temperature extremes while allowing transmission of light, providing ventilation, accommodating building movements, and forming a relatively lightweight cladding system. Problems associated with any one of these areas can compromise overall building performance. As with most materials, windows deteriorate with age, and some repair and maintenance is necessary. The original performance of these building elements is typically reduced over time, which can adversely affect interior conditions and surrounding building construction.
Avoiding Water Penetration in Windows
BSD Rain Control in Buildings | Building Science Corporation
In order for water to penetrate a wall, all three of the following conditions must be true at the same time and location:. Rain, striking a wall at an angle, may have enough horizontal momentum to drive it through an opening see Figure 2a. The water will penetrate the wall if the opening is continuous and properly oriented. The solution in Figure 2b, shows how a labyrinth shaped opening interrupts the flow of water. Other solutions include covering the gap, or orienting the opening downward similar to a louver or baffle 4. The adhesive and cohesive properties of water allow it to cling to a surface and even oppose gravity. In Figure 3a, water is flowing along the underside of the block until it reaches the edge where it drips onto the backside of the wall.
Causes of Water Penetration and Damage
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Driving rain deposition is quantitatively the largest single source of moisture for most walls and roofs leading to building enclosure deterioration. Controlling rain penetration is, therefore, one of the most important parts of a successful moisture control strategy which involves understanding and predicting moisture movement within and through the enclosure to improve building enclosure performance, particularly durability. This document will consider rain control from a general to a specific level. The following sections will cover: basic moisture control principles that should be employed in the design of above-grade building enclosures; driving rain as a moisture load on walls; a classification system of the various rain control strategies available for walls; and finally, good design practices for walls.