... a door or tilt the top of the sash into your room. It balances the ventilation and dust/water resistance.2 ... .EPDM sealing ,maximizing air tightness ,water tightness and noise insulation performance.14.Professional glass pads can effectively resolve sagging issues.15 ... Standard C-Groove system applied.18.Multi-locking system ,dramatically increase the performance of water tightness ,and security.