Screens and fresh air

WA Health’s advice for healthier indoor air starts with the windows: open windows and doors regularly to let fresh air circulate, and open them when using chemical cleaners and sprays, following the product’s instructions.

Victoria’s Better Health Channel, in advice written for COVID-19, says bringing outdoor air in is the simplest way to ventilate a home, and if it is safe, that means opening doors and windows. Air moves best across a space, so it suggests opening doors, windows and vents on opposite sides of a room, and notes that even a slightly open window can help. Where the weather is too cold, or someone needs to watch an open window, it suggests opening the window for a set time instead, for example 10 minutes in every hour.

A screen is what lets a window stand open without letting insects in: healthdirect’s reason for insect screens is to stop mosquitoes getting inside, and Queensland’s advice for rooms without them is mosquito nets, particularly where people sleep. Where biting midges are a problem, WA Health suggests a fine mesh on doors and windows, because midges can fit through standard fly screens, and adds that ceiling fans may discourage them from biting.

For houses, the National Construction Code’s Housing Provisions ask that habitable rooms, bathrooms, laundries, sanitary compartments and any other room a person occupies be ventilated. One way is by windows, doors or other openings that can be opened, with a ventilating area of not less than 5% of the room’s floor area, opening to a suitable court or space open to the sky, an open verandah or carport, or an adjoining room under the code’s rules for borrowed ventilation.

The code’s explanatory note says a window’s ventilating area is measured as the size of its openable sash, whatever the kind of window and regardless of any restriction on how far the sash opens. As an illustration with an invented room: a bedroom 4 m by 3 m has 12 m² of floor, and 5% of that is 0.6 m² of openable sash.