Natural ventilation, or lack of.
The modernist triumph of bare-arse glass for fully airconditioned office buildings has become the ubiquitous answer for high rise residential.
Brisbane is now plagued by them. Pretty much the same for other Australian capitals with different climates.
The first dilemma on observation is: is it office or residential. A slightly open sash is espied.
Maybe residential – since when has an office building had an openable window?
Through a gap in the onslaught of glass a recess in the façade is seen; maybe a veranda camouflaged by the glass balustrade merging into the amorphous sheen. Fair chance it’s residential. (I detest modern glass balustrades.) Then the open slit of a window leads one to wonder: is that all the natural ventilation needed to comply with the National Construction Code [NCC] for habitable rooms. It is minuscule.
The NCC 2019 Vol. 2 Part 3.8.5 says:
184.108.40.206 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 …
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.
“irrespective of the restrictions on the sash” I interpret as it can open 1mm and comply. This clause flabbergasts me, and I want my understanding to be wrong.
Should readers of the codes – as I did – imagine the 5 per cent ventilation area would be free of obstruction, you are wrong. What is the actual open area? An awning window, as the now only seen answer in these high-rise unit blocks is the example.
Allow a room of 12 square metre – average for a bedroom. At 5 per cent of the habitable floor area 0. 6 sq m results giving a sash 1 metre high by 0.6m. Child safety requirements result in an opening of 125 mm maximum.
To always comply, and avoid litigation, few to none would not lessen the 125 mm. At 125 mm the true open air area is 0.15 sq m. Four windows are now needed to achieve 5 per cent – not one!
If the window is insect wired more ventilation is blocked.
Some councils demand “don’t perve-on-your-neighbour screens”. The maximum open area of such screens in Brisbane is 25 per cent up to 1700 mm above floor level. So, 75 per cent more air is blocked.
If the NCC believes in 5 per cent of the floor area –-nothing else – the clause should become:
With a ventilating area not less than 5 per cent of the floor area of the room to be ventilated.
The ventilating area is measured as the unobstructed area at 90 degrees horizontally to the wall. For any obstructions the opening size is to be increased to ensure the minimum. Common obstructions are: sashes in their most open position, fixed insect screens and any other fixture.
The NCC has eight climate zones in the energy efficiency section and none in ventilation. Ventilation minimums must also vary for the zones.
I lived in Port Moresby in a Commonwealth government designed house built after WW2 like those in Darwin. The ventilated wall area of all rooms was close to the floor area: 100 per cent – and the NCC says 5 per cent for Darwin is enough!
While I lead an almost fully unairconditioned life, many readers possibly went from an AC birth, home in an AC car, to an AC house, to an AC school, to an AC workplace and view an openable window as unnecessary.
Recent events with Covid 19 must cause them and the NCC to be concerned. It is well to remember a report years ago that concluded the healthiest housing was the most air leaky.
Professor Lidia Morawska director of QUT’s International Laboratory for Air Quality and Health said on ABC News:
“We don’t have any quantitative data about this and, of course, every environment is different, but what I do if I go to any place, I look around. How many people are there? How, according to my judgement, is the place ventilated?
“If I see that potentially in not ventilated places, the risk is high, I don’t go in there.”
On Coronavirus and AC she adds,” [Recirculation] can bring back the virus into the supplied air. So, ventilation as high as possible and no air recirculation.”
Why does the NCC have such a small minimum at 5 per cent and then allow the area to potentially be zero per cent and comply?
Maybe: [a] developer lobbying to cut costs as openable windows cost more than fixed glass, and now AC units are foolishly considered as essential as underpants for modern life.
The flogging real estate agent would say,” If it’s not there, it won’t sell.” [b] child safety is viewed as primal and all other requirements are sacrificed.
Neither cuts the mustard.
Developers waste money on multiple toilets based on the same “won’t sell” argument. If such indulgences must go for openable windows to be built at the same cost—great! Money spent where it should be.
I find it incomprehensible that the Australian Building Codes Board (ABCB) — drafters of the NCC– would allow a non-true ventilatable area to be reduced for safety reasons when it is dead easy to solve the child danger problem and have the ventilation.
Maybe they should ask their parents how they stopped them falling out of cots with more than 100 per cent ventilation area.
If there are any doubts about fresh air, recent images of 14-day quarantines exiting to the street from rooms – most likely with fixed glass and only AC in expensive hotels – exclaiming with euphoric glee: “Fresh air! Fresh air!” And the high-rise Victorian Housing Commission flats with windows opening to a slit at the sill, successfully fulfilling can’t-fall-out-of-window demands while looking like a prison, should prove the health benefits of access to fresh air.
After all, external air is ultra-violently sterilised [sunlight] as opposed to toxicogenic recirculated air.
ABCB must redress what they have allowed to happen and what healthy building design needs to be, as revealed by Covid19.
If they applied the same logic to a fire escape door as the ventilation area of a window sash it would be: “the fire door has to be of a size to allow two humans to pass through simultaneously. The escape area is measured as the area of the door irrespective of the restrictions placed on the door.”
Finally, to avoid discrimination against fresh air, I wish to suggest to the ABCB: an openable window can be closed, fixed glass cannot be opened.
Russell Hall is a Brisbane-based architect with experience in residential, retail, commercial and industrial design. He is interested in designing whatever comes along.
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