The basic mechanism for natural ventilation in a building involves air flowing through purpose-made ventilator openings. These ventilators must be carefully designed as natural ventilation driving forces are weak compared to the dynamic forces created by mechanical systems. This paper describes a series of experimental parametric studies that investigated how components within a ventilator (in this case louvers and wire mesh screens) interacted. Air flow measurements through the individual louver and mesh components were compared to the air flow through mesh / louver combinations. The effect of altering the distance between the louver and the mesh was also investigated. Finally, a small comparative study was made between some of the experimental data and CFD predicted values. Initial results indicated that the air flow through a louver-mesh combination was always significantly less than the flow through an individual mesh or individual louver. A louver with a small diameter mesh (insect screen) was experiencing air flow reductions of the order of 50% while for a large diameter mesh (bird and animal screens) the reductions were approximately 20%. Providing a separation between the back of the louver and the mesh produced small improvements in the air flow, from 2% to 12%, depending upon the size of the separation and the louver blade inclination. The CFD analysis showed that agreement improved as the louver inclination angle increased (greater flow resistance), but that further work is need to improve the agreement at low inclination angles.