Natural ventilation seems hard to come by; with all of the glass enclosing fully airconditioned office buildings positioned as the resolution for high rise residential living units.

Brisbane and many other developments are filled with them.

The first question to ask is: office or residential? An opened sash is espied.

Let’s start with residential.

By way of a gap in the onslaught of glass, a recess in the façade is visible; perhaps a veranda concealed by the glass balustrade blending into the amorphous sheen.  This describes a residential structure. Some wonder if the window slit that remains can supply the natural ventilation required to fulfill the National Construction Code [NCC] for livable rooms.

The NCC 2019 Vol. 2 Part 3.8.5 says: Ventilation requirements

Ventilation must be provided to a habitable room, sanitary compartment, bathroom, shower room, laundry and any other room occupied by a person for any purpose by any of the following means:

[a] Openings, windows, doors, or other devices which can be opened—

With a ventilating area not less than 5% of the floor area of the room required to be ventilated …

Explanatory information:

The ventilating area of the window is measured as the size of the openable sash of the window. This is the case regardless of the type of window, i.e. whether it is an awning, casement or sliding window and irrespective of the restrictions on the openable sash.

The slit window’s 5 per cent ventilation area may be beset by an obstruction, with the open window actually taking the form of an awning window.

For a room of 12 square metres, typical for a bedroom, at 5 per cent of the habitable floor area, a space of 0. 6 sq m remains; allowing for a sash 1 metre high by 0.6m. Child safety standards produce an opening of 125 mm maximum.

To follow the rules, and avoid legal problems, few to none would not reduce the 125 mm space. At 125 mm, the genuine open-air area is 0.15 sq m. A bank of four windows are required to achieve 5 per cent.

If the window is wired for insects, additional ventilation is blocked.

Some councils demand neighbour-friendly screens, allowing for a maximum open area of these screens in Brisbane is 25 per cent up to 1700 mm above floor level. In this instance, 75 per cent more air is blocked.

If the NCC supports 5 per cent of the floor area, the corresponding clause should become:

With a ventilating region not less than 5 per cent of the floor area of the subject space to be ventilated.

Explanatory Information

The ventilating region is measured as the open area at 90 degrees horizontal to the wall. For any obstructions, the opening area is to be widened to guarantee the minimum. Common obstructions take the form of sashes in their open position, designated insect screens and any other fixture.

The NCC maintains eight climate zones in the energy efficiency section and none in ventilation. Ventilation minimums must differ across zones.

Most of us grew up in air-conditioned areas. Yet with the onset of COVID-19, we must reconsider the issue.

Professor Lidia Morawska, director of QUT’s International Laboratory for Air Quality and Health, says that our atmosphere demands well-ventilated areas that do not allow for air recirculation.

Openable windows must be more economic to produce, many believe. Fresh air is essential, as exterior air contains ultra-violently sterilised sunlight, instead of toxicogenic recirculated air. Let the sunshine and fresh air in for the very best results.


*This article was first published in The Fifth Estate.