construction or as a retrofit referring particularly to fig1 there is illustrated a conventional block wall 140 formed of several courses of blocks 142 to provide for water inflow or outflow from an enclosure defined by the block wall and to provide for ventilation a block has been removed as depicted by a void or opening 144 to ensure that blocks 146 148 above the opening will not have a tendency to migrate downwardly into opening 144 a rectangular brace 150 may be inserted at the front and back of the opening this brace would provide support for the overlying blocks and prevent splitting or other damage to block wall 140 due to migration of blocks 146 148 and any further overlying blocks a flood vent 152 as particularly illustrated in fig1 and 19 includes a louvered panel 154 having a plurality of louvers 156 which comply with code requirements for flood vents a rodent screen 158 having a plurality of apertures 160 as described above is mounted adjacent interior surface 162 of louvered panel 154 and within lip 164 extending about the louvered panel to retain rodent screen 158 in place strips of double sided adhesive tape 166 are placed adjacent the interior surface of border 168 of the rodent screen and in corresponding locations on interior surface 162 surrounding louvers 156 of the louvered panel alternatively the.