AS 1668.2 and clinical ventilation
Why the base building air conditioning that suits an office frequently cannot serve a clinic, and what to check before you sign.
The short answer
Of everything that can make a tenancy unsuitable for a clinic, ventilation is the one nobody looks at on the inspection. You can see whether there is a step at the door. You cannot see whether the air handling unit has any spare capacity.
Key points
- AS 1668.2 governs mechanical ventilation; the NCC makes it mandatory.
- It sets outdoor air rates by space type and required exhaust for specific rooms.
- Base building plant sized for an office often cannot serve a partitioned clinic.
- Carving one open tenancy into twelve rooms changes the ventilation problem entirely.
- Ask about capacity, zoning and whether you can add plant, before you sign.
Of everything that can make a tenancy unsuitable for a clinic, ventilation is the one nobody looks at on the inspection. You can see whether there is a step at the door. You cannot see whether the air handling unit has any spare capacity.
What AS 1668.2 does
AS 1668.2, The use of ventilation and airconditioning in buildings, Part 2: Mechanical ventilation in buildings sets out how much outdoor air a space needs and what has to be exhausted. The National Construction Code calls it up, which is what makes it mandatory rather than advisory.
Two mechanisms matter for a clinic:
Outdoor air rates. How much fresh air a space requires, which depends on what the space is used for and how many people are in it. A consulting room and a waiting room are not the same calculation.
Exhaust. Certain spaces must be exhausted rather than recirculated. Sanitary facilities, dirty utility, and depending on scope, procedure and treatment areas.
Why an office system often can’t do it
This is the practical heart of it, and it catches almost every first-time tenant.
A base building air conditioning system was sized for the building's intended use. In a commercial tower that means open-plan office: a large volume, few partitions, a predictable occupancy, and air that can move freely across the floor.
Then you arrive and divide that tenancy into twelve enclosed rooms with doors that close.
Three things break at once. Air distribution: each room now needs its own supply and its own return, and the existing ductwork was not laid out for that. Capacity: the outdoor air component may be adequate for an office occupancy and not for yours. Zoning and control: a consulting room where a patient is undressed and a waiting room full of coats have opposite requirements, and one thermostat for the whole floor serves neither.
Add required exhaust from utilities and sanitary facilities, which has to discharge somewhere the building will allow, and a system that was perfectly adequate becomes a project.
What that means commercially
One of three outcomes, and it’s worth knowing which before you sign:
- The base building system can serve you with reworked distribution inside the tenancy. Ordinary fitout scope.
- You install supplementary plant. Which needs somewhere to go, with structural capacity, acoustic separation and a maintenance route. On many tenancies that place does not exist or the landlord won’t permit it.
- The landlord upgrades the base building. A negotiation, with a timeline and a cost that’s not yours to control.
Where it goes further than the standard
AS 1668.2 is the baseline. Some clinical spaces need more.
Pressure-controlled rooms require the air to move in a specified direction relative to adjacent spaces, which is a design problem rather than a rate. Procedure rooms and theatres carry filtration and air change requirements that come from health facility guidance rather than from the ventilation standard alone. Laboratories with fume cupboards need make-up air so that exhausting the cupboard doesn’t pull the room into imbalance.
All of those are mechanical engineering, designed for your specific scope and commissioned with documented results before the occupancy permit issues.
What to ask before you sign
- What is the base building system, and what outdoor air capacity is available to this tenancy?
- Can it be zoned and controlled from within the tenancy, or is it a whole-floor system?
- Is there a path for exhaust to discharge, and will the landlord permit the penetration?
- If supplementary plant is needed, where would it go, and is that space available to me?
- Who pays if the base building system turns out to be inadequate?
The last one is a lease question, not an engineering one, and it is worth resolving at heads of agreement, not during construction. It sits on our lease checklist for that reason.
AS 1668.2 is a purchased document and it’s revised. Rates and requirements should come from the current edition through a mechanical engineer, not from a summary.
Sources and further reading
AS 1668.2 is a purchased document and is revised. Rates and requirements should come from a mechanical engineer working to the current edition.
Source for AS/NZS 4815 and 4187 reprocessing, AS 1428.1 access and AS 1668.2 ventilation. The standards themselves are purchased, not free.
The National Construction Code: building classification, fire separation, egress, sanitary provisions and access.
Room-by-room design guidance and standard components used across Australian health projects, including consulting, treatment and sterilising rooms.
Questions
What is AS 1668.2?
The Australian Standard for the use of ventilation and airconditioning in buildings, Part 2: mechanical ventilation. It sets outdoor air rates by space type and the spaces that must be exhausted rather than recirculated. The National Construction Code calls it up, which makes it mandatory.
Can base building air conditioning serve a medical clinic?
Sometimes, and often not without work. A system sized for open-plan office use has to cope with a tenancy divided into a dozen enclosed rooms, each needing its own supply and return, plus required exhaust from utilities. Distribution, capacity and zoning all have to be checked.
What happens if the building's system isn’t adequate?
One of three things: the distribution is reworked inside the tenancy, you install supplementary plant somewhere with structural capacity and landlord consent, or the landlord upgrades the base building. The third is a negotiation you do not control, and that is why it belongs in the lease discussion.
Do consulting rooms need more ventilation than an office?
The rate depends on the space type and occupancy rather than on the word 'medical', but the practical answer is usually yes once you account for enclosed rooms, exhaust from utilities and sanitary facilities, and the need to control zones independently.
Is AS 1668.2 the only ventilation requirement for a clinic?
It’s the baseline. Procedure rooms, theatres and pressure-controlled rooms carry additional filtration, air change and pressure requirements from health facility guidance, and laboratories with fume cupboards need make-up air designed alongside the exhaust.
Send us the floor plan
A site assessment tells you what the tenancy can take and what it will cost to get there, ideally before you have signed for it.