Preserving a building façade is often a first requirement in historic building preservation. Historic windows can be a significant part of the historical façade. A big challenge can be incorporating modern serviceability, safety and security requirements into the preservation and renovation of historic windows. One way is to retrofit from the inside. We recommend retrofitting and hardening from the inside where you can. Often, that means adding a low profile supplemental window system on the interior and interior structural supports to carry the supplemental window loads to floor plates above and below. Interior retrofits preserve exterior aesthetics without significantly impacting interior workable space.