Division 1—Prescribed qualifications
In this Division—independent technical expert means a person who, in relation to building work—
(a) is not the building owner or an employee of the building owner; and (b) has not— (i) been involved in any aspect of the relevant development (other than through the provision of preliminary advice of a routine or general nature); or (ii) had a direct or indirect pecuniary interest in any aspect of the relevant development or any body associated with any aspect of the relevant development; and (c) has engineering or other qualifications that the relevant authority is satisfied, on the basis of advice received from a relevant professional association or a relevant registration or accreditation authority, qualify the person to act as a technical expert under these regulations.
(3) In subregulation (2)—professional engineer means a person who is—
(a) a corporate member of the Institution of Engineers, Australia who has appropriate experience and competence in the field of civil engineering; or (b) a person who is registered on the National Professional Engineers Register administered by the Institution of Engineers, Australia and who has appropriate experience and competence in the field of civil engineering.
These references typically differ only in the subregulations they relate to, and are generally concerned with roads, stormwater and earthworks.
First and foremost the primary requirement is independence.
At the simplest could say that:
Two idiots independently reaching the same conclusion is far better for the public interest, than one idiot acting as self appointed authority. It is through the continuing challenge from others that real competence is developed, not via a once off assessment and appointed position of authority. Far too many of the self-certifications flowing in from other states are worthless scrap paper. The certificates contain inadequate information to permit an independent technical check on the suitability of a development proposal.
It is not so much as that building officials in SA want to see the calculations, but that the requirements of the Building Code of Australia (BCA), is based on adequate evidence-of-suitability, and the certifications available are not considered adequate and the proposals are otherwise of questionable suitability.
At the simplest there is just a plain lack of effort defending the development proposals: besides a lack of evidence-of-suitability, the descriptions of the proposals are often also inadequate. The very lack of thought and consideration is the reason for the regulations being in the way. The regulations are only really a hindrance to those who choose not to do the right thing.
... more on the issues of independence later.