ing installation.

3. To be absolutely safe against water being pumped back through a weep hole by wind pressure, the hole can be drained through a vertical weep tube that exits the wall a distance below the point that is being drained. If there is a vertical distance of 10" (250 mm) between the inlet and outlet of a weep tube, for example, it would take a wind of approximately 140 mph (225 km/ hr) to pump water up and into the building through the tube. This is the principle of the upstand applied in a slightly different disguise, using the same table to equate heights of water to pressures of air.

When detailing an upstand, remember that its ends must be dammed carefully at vertical joints or the water will simply drain out of the ends to become unwanted leakage. In aluminum cladding details, end dams are often plugs molded of synthetic rubber. ■

2. horizontal Joint Between Curtain Wall Panels

3. Weep Tube in Curtain Wall

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