New Zealand has the highest rate of car ownership per capita in the world, with 869 vehicles per 1000 people.  Improvements to public transport and the rise of inner city living is unlikely to quell this appetite for the automobile because the car is, and will likely remain, a symbol of freedom.  It’s an immediate means of escape, if only for a Sunday drive.  Additionally, research from German manufacturer Continental Tyres discovered that for many drivers their vehicle is a place to escape the world and a few minutes travel every day has a positive impact on mental health (although we presume this precludes being stuck in Auckland traffic).  

With the continued rise of shopping malls and need for medium density housing, we’re seeing more people in smaller spaces and this feeds into demand for more multi-storey car parks, either above ground or underneath.  Until our national fleet has completely transitioned to electric vehicles (if this ever happens) exhaust fumes from internal combustion engine vehicles require adequate ventilation to ensure the air is healthy for car park users.

Different Car Parks, Different Ventilation 

There is no single ventilation solution for car parks.  At the most basic level, it will depend on whether the car park is above ground or not.  

Multi-storey car parks above ground can use natural ventilation if the sides are open enough, reducing the need for mechanical ventilation (while not removing the need entirely).  The ventilation solution here will be impacted by the architectural design.  For example, if the car park has a perforated aluminium facade, the open rate of the perforated panels needs to be taken into consideration.

Below ground car parks will require mechanical ventilation, using extractor fans, jet fans or induction fans.  There has been some discussion that tunnel theory can apply to underground car parks but that’s really not possible.  The structures are usually too complex, with numerous bends, and the vehicles entering/exiting aren’t moving quickly enough to become an energy source for airflow. 

In both structures, if there is an attached loading bay, then this will require its own solution due to the design of these bays and the types of vehicles using them, typically being diesel powered heavy goods vehicles.  

Why Car Park Ventilation is Important

The reasons for the importance of car park ventilation are immediately obvious to most. Carbon monoxide (CO) from vehicle exhausts can lead to serious health issues.  The rapidity of which this can happen may come as a surprise to some though.  

Carbon monoxide poisoning is essentially a form of asphyxiation caused when the CO combines with haemoglobin, lowering its oxygen carrying capacity.  Where the CO level in the air is extreme (12,800 ppm) it can take under 3 minutes to lead to death.  This is extended to 30 mins at 3,200 ppm, and 2 hours at 1,600 ppm.  Even at 200 ppm, headaches, dizziness and nausea lasting for a few hours can be expected.  

For these reasons, many car parks will require continuous monitoring of CO levels, with an early warning system triggering notifications should levels exceed the permissible limits.   

Proper ventilation is also needed for fire safety.  The design of the car park ventilation system needs to provide a safe evacuation route for any occupants and should be both time to exit and enough breathable air to do so without significant health risk.  It should also aid the efforts of firefighters and help control smoke, preventing its spread.  

Car Park Ventilation and the Building Code

The section of the New Zealand Building Code (NZBC) concerned with car park ventilation is Clause G4, which states ‘natural ventilation of car parks shall comply with the natural ventilation part of AS 1668.2 Section 7’ and that the ‘mechanical ventilation of car parks shall comply with the mechanical ventilation part of AS 1668.2 Section 7.

What Section 7 does is define the amount of ventilation needed based on; the type and quantity of vehicles using car park, anticipated total time of engine use, time occupants will spend inside the car park, and if there is a need for increased ventilation due to extended exposure (i.e. car park attendants or rental vehicle businesses operating from the car park.  

Car Parks & Natural Ventilation

The requirements for naturally ventilated car parks are suitably prescriptive and a full overview of them is beyond the limits of this article (you can contact us to discuss them in more detail). What we can do here is draw your attention to the main points.  

For a start, natural ventilation isn’t compatible with underground structures so to meet code the lowest point of the car park floor should be no more than 1.2m below ground.  

Proximity to natural ventilation openings is also important.  All parts of the car park should be within either 20m of a ventilation opening, within 30m of two openings on separate walls, or within 7m of the shortest path between any natural ventilation opening and any other natural ventilation opening.

The open areas required for natural ventilation are dependent on the number of vehicles in the immediate area.  For example, if the parking is for 6 vehicles or less then an open area of not less than 5% of the floor area, equally distributed on at least 2 walls, is sufficient.  If there is parking for more than 6 vehicles, then openings need to be at least 12.5% of the floor area.  

An important distinction here is that this is for parked spaces.  Where queuing is expected the requirements change and the open area changes significantly, having to be at least 90% for the full length of the queuing area.  

Car Parks & Mechanical Ventilation

For car parks with more elaborate facades, the design of which might impact the open area requirements, or where parking spaces are underground, mechanical ventilation will be required.  

The requirements here are generally based on the airflow rates to supply air and exhaust air openings, proximity of parked vehicles to air openings, the number of vehicles and vehicle type.  For example, airflow rates at each supply air or exhausted air opening need to take into account the number of vehicle spaces through which the air passes.  Which makes sense really.

Also, where enclosures have exhaust ventilation only, every part of the car park must be within 7m of the shortest path between any exhaust air or relief air opening, with no more than 10% of the area more than 3m away from the shortest path between any exhaust air or relied air opening.  In other words, when you park in an underground car park, take a look around as you should be close to some sort of mechanical ventilation.  

Other Requirements for Car Park Ventilation

We mentioned loading docks earlier and the need for these to meet specific criteria, owing to the type of vehicles usually doing the loading and unloading.  If a loading dock is located more than 10m from an external wall with ventilation, it has to be ventilated by an exhaust system with an airflow rate of not less than 1500 L/s per vehicle docking space.

Queuing areas are similarly subject to more stringent controls.  Here, exhaust air intakes must be uniformly distributed for the full length of the queuing area, meeting exhaust airflow rates of 225 L/s per metre of each exit lane and 150 L/s per metre of each entry lane.  

As urban densification continues, the importance of proper ventilation in car parks and other enclosed spaces will likely become stricter and subject to more regulation.  The simple act of fitting ‘more’ into ‘less’ demands such.  Add in the risk of future Covid like outbreaks and we see the demand for ventilation increasing and new projects might want to consider not just meeting code, but exceeding it.   

Where there is a will to do that, the answers aren’t found in legislation. But they can be discovered with a phone call to us.  We’d be happy to help.