are often applied to one or both of the internal surfaces (i.e. the ones facing the air gap) of other forms of modern insulative glazing, in order to prevent loss of heat through infrared radiation. Slightly less effective "hard" coatings are still suitable for evacuated glazing, however. Furthermore, because of the atmospheric pressure present on the outside of an evacuated glazing unit, its two glass sheets must somehow be held apart in order to prevent them flexing together and touching each other, which would defeat the object of evacuating the unit. The task of holding the panes apart is performed by a grid of spacers, which typically consist of small stainless steel discs that are placed around 20 mm apart. The spacers are small enough that they are visible only at very close distances, typically up to 1 m. However, the fact that the spacers will conduct some heat often leads in cold weather to the formation of temporary, grid-shaped patterns on the surface of an evacuated window, consisting either of small circles of interior condensation centred around the spacers, where the glass is slightly colder than average, or, when there is dew outside, small circles on the exterior face of the glass, in which the dew is absent because the spacers make the glass near them slightly warmer. The conduction of heat between the panes, caused by the spacers, tends to limit evacuated glazing's overall insulative effectiveness. Nevertheless, evacuated glazing is still as insulative as much thicker conventional double glazing and tends to be stronger, since the two constituent glass sheets are pressed together by the atmosphere, and hence react practically as one thick sheet to bending forces. Evacuated glazing also offers very good sound insulation in comparison with other popular types of window glazing. Building code seismic requirements The most current building code enforced in most jurisdictions in the United States is the 2006 International Building Code (IBC, 2006). The 2006 IBC references for the 2005 edition of the standard Minimum Design Loads for buildings and other Structures prepared by the American Society of Civil Engineers (ASCE, 2005) for its seismic provisions. ASCE 7-05 contains specific requirements for nonstructural components including requirements for architectural glass. Danger of reflected sunlight If incorrectly designed, concave surfaces with extensive amounts of glass can act as solar concentrators depending on the angle of the sun, potentially injuring people and damaging property. Toughened