Like any question that pertains to a law in Australia, particularly a federal (Commonwealth) law, the answer is 'maybe' or 'it depends'.
Ramps are more or less expected at Government Buildings but you don't always get them at private buildings, so is it mandatory? Well, look at it this way, our office on the ground floor of 105 Molesworth Street has ramps to get into it. But the actual building itself (to get upstairs to where the lawyers, accountants etc. are) only has stairs which then lead to elevators. Is this discriminatory?
This question is not really a WHS one but more a human rights matter, but Human Rights, Industrial Relations and a lot more things are slowly falling under the umbrella of WHS, luckily I am pretty familiar with Discrimination law.
Australian Discrimination law is pretty well based in common sense. The right to enter a premises a non-disabled person has access to regardless of disability is outlined in the Disability Discrimination Act 1992 (Cth), s 23.
So this doesn't mean that a person can enter a top secret military establishment just by being disabled, but if a non-disabled person has the right to be there and the disabled person meets all the same criteria (i.e. Security clearance and authorisation in this case) then they must not be barred from entering.
But let's use a more common example, blind people going out to eat. Blind people are usually assisted through a cane or an assistance dog (or both). Even if a premises has a 'no dogs' policy, as the dog is seen as essential in managing the disability the dog is permitted to stay with the owner provided the owner shows they can exercise control over it.
So, we've established the fundamentals - you can't choose to kick a disabled person out of your business based purely on their disability and any reasonable aid they need in managing it, so where does it stand with ramps?
Well, this is basically a case by case thing. For instance some older courthouses in the state are still being retrofitted with ramps as the only access is stairs which is a huge barrier for older persons who may use canes and is practically a death sentence for anyone in a wheelchair.
Generally, anything considered 'essential' to the public must have a way for disabled people to enter. This would include;
AusPost Offices (agents may not be considered essential)
Hospitals
Court Houses
Police Stations
Utilities providers
Banks
Public Transport stations and vehicles
Supermarkets/shopping centres
Medical Centres
As you can imagine, if you are in a wheelchair you still need to be able to access all of the above just like any able bodied persons.
But does that mean that it is legal for say an accountant to have a stair only building? Well, maybe. If that accountant isn't stopping disabled people from using their services and can make other arrangements (i.e. meet elsewhere, meet virtually) I don't see that being seen as discrimination. But if an accountant ever said "no, you can't be my client because you're disabled and I can't have disabled people in my office" that is almost certainly discrimination.
To give an examples of private businesses I think should have disability access;
Compensation Lawyers (Workers Comp or General Litigation) Goes without saying, most of your clients will likely be disabled which is probably why they are suing someone. If a disabled client can't even access your building - that's a poor start.
Banks I don't think I've seen a bank that is not accessible to disabled persons. The picture that appears from this article is from Summerland Credit Union about 2 doors down from our office.
Employment Agencies Obviously as it is also illegal to discriminate against employees with disabilities (with some exceptions) you must have your buildings accessible for disabled people seeking work.
Training Organisations The right to education and further training is open to all, regardless of disability. For that reason any RTO (within reason) must be able to accommodate a disabled person.
So, in conclusion - if you have a ramp already (like we do), great - keep it and maintain it. If you don't you need to consider if the cost of installing one exceeds the good to the community. If you are in a niche industry like us, we probably could get away without one. But if you are a service that is open to everyone (i.e. banking, law, healthcare) then you should be attending to client needs.
If you suspect a business has been violating human rights, you can report them to humanrights.gov.au