Typical double-hung and casement exterior windows with no storm windows provide between 22 and 27 dBA of noise reduction from the outside. This noise reduction is the actual measured difference between indoor and outdoor sound pressure levels with the actual installation. It is usually less than any laboratory rating (such as STC or TL) because laboratory ratings do not consider actual installations that may not be fully sealed. These ratings also do not account for the absorption in the room in which measurements are performed. Replacement windows are double-paned with two windows 2 in (5 cm) apart. These are shown in Figure 3.34 from the inside and Figure 3.35 from the outside. Figure 3.36 shows a gliding replacement window. In each case, these windows offer noise reductions in the range of 33 to 38 dBA.