Shadow boxes are commonly used in curtain wall construction but can be problematic if not designed and detailed correctly and appropriately for the climate. Much has been written about shadow box design, both successes and failures, but there is no consensus about how, or if, the cavity should be vented. There have been 3 primary approaches to treating the cavity between the glazing and the shadow box back pan: venting directly to the exterior environment, venting directly to the interior building environment and sealing the cavity. Venting the cavity directly to either the exterior or the interior building environment introduces moisture- and particulate-laden air that can condense under certain climatic conditions and will likely deposit dust and debris on the interior surfaces of the cavity, creating both permanent and temporary aesthetic concerns. When venting to the exterior, cold, winter air is allowed inside the cavity and on the interior side of the thermal break, potentially cooling the perimeter mullions to a point where condensation will form on their interior surfaces. Sealing the cavity eliminates both of these issues, but there is some evidence that heat and pressure may build up to a point where it could damage the glass and degrade the sealants and coatings inside the cavity. After considering all of the options, a modified version of venting to the exterior appears to address most of the issues. This approach vents the cavity into the vertical mullions, which ultimately connect to the exterior environment, but do so indirectly, relieving the heat and pressure but also somewhat tempering the exterior air that is allowed to enter.