Prestofen Shed Windows feature an exclusive PVC (polychloride vinyl) frame that houses a single 3mm glass pane. Easily installed, these windows provide optimal insulation at far lower cost than regular windows. This picture style frame with 6 light grilles requires no maintenance and features a removable grill. It will always stay white – no fading or yellowing. The exterior window frame is 16-5/8 X 34-3/4" and the interior window frame is 14-1/4 X 32-1/4". The necessary opening for window installation is 14-3/8 X 32-3/8.