Example C5: Background ventilators and intermittent extract fans

For a two storey semi-detached house of 84 m2 floor area, paragraph 2.19 shows that the equivalent background ventilator area is 40000 mm2. To maximise the air flow through the dwelling by encouraging cross ventilation, it is best to locate similar equivalent areas of background ventilators on opposite sides of the dwelling. Calculate the percentage window opening area (percentage of floor area) for each room having an external wall. Using Appendix B with an opening angle of 20° gives 1/10th of the floor area. Therefore, for a living room of 14.8 m2 floor area there should be a window opening area of at least 1.48 m2. This calculation should be repeated for each habitable room.