AS 2870 vs NCC 1

[LiamJS]

There are discrepancies between AS 2870 and NCC for the footing heights provided in tables. Why is the reason?

 

[LiamJS]

Anyone there using the standards? Which one do you adapt as deemed to comply?

 

[Retrograde]

What are the actual disrepancies? Which tables in particular are you talking about?

 

[sdz]

Liam, you're probably better posting in AS/NZS (au/nz) Code Issues
More information with table numbers would be helpful.

 

[LiamJS]

Thank you for your answers.

For example :
Stiffened Raft Class S Articulated Full Masonry: AS2870 Figure 3.1=500mm vs NCC 2019 Table 3.2.5.4b = 400mm

Another example:
Stiffened Raft Class M Full Masonry: AS2870 Figure 3.1=950mm vs NCC 2019 Table 3.2.5.5a = 800mm

There are others but I gave two examples. Another thing is that the standard is in "Pending Revision" status, and this makes things more confusing.

 

[LiamJS]

I saw AS/NZS (au/nz) Code Issues part. Next time I will post there.

 

[Retrograde]

I confess that I had no idea those tables are in the NCC. I have always just used AS 2870.

 

[LiamJS]

What makes sense to me is that AS 2870 is deemed to comply; NCC is minimum which no engineering solution can go below it.

However, I need clear statements about these somewhere in AS 2870 or in NCC to be sure. I couldn't find.

 

[Euler07]

The NCC and Australian Standards are written by different groups who have different opinions and different goals.

Regarding the tables, I remember the divergence started with AS2870-2011. If you look at the earlier versions of AS2870 then they should be the same. You would have to confirm this, but I remember there being some big drought in the eastern states which caused cracking of walls on clay sites and this led to AS2870 designs becoming heavier. I think the NCC may have disagreed with the change and left it as is.

Most companies I know kept the original design that they had been using for decades and didn't follow the upgrade.

What makes sense to me is that AS 2870 is deemed to comply; NCC is minimum which no engineering solution can go below it.

Both the NCC tables and AS2870 are deemed to comply. Therefore following those tables is not mandatory.

Hope this helps.

 

[LiamJS]

The NCC and Australian Standards are written by different groups who have different opinions and different goals.

Regarding the tables, I remember the divergence started with AS2870-2011. If you look at the earlier versions of AS2870 then they should be the same. You would have to confirm this, but I remember there being some big drought in the eastern states which caused cracking of walls on clay sites and this led to AS2870 designs becoming heavier. I think the NCC may have disagreed with the change and left it as is.

Most companies I know kept the original design that they had been using for decades and didn't follow the upgrade.


Both the NCC tables and AS2870 are deemed to comply. Therefore following those tables is not mandatory.

Hope this helps.

Thank you for the background story. That explains the confusion. Existence of two deemed to comply solution is really messed up. Then one should do calculations to go below any of them.

Another point is about which one is binding legally. While engineering part is not clear, legal part will be more confusing. They should solve this as soon as possible.

 

[Euler07]

Another point is about which one is binding legally. While engineering part is not clear, legal part will be more confusing. They should solve this as soon as possible.

Neither of them are legally binding since they are both deemed to satisfy solutions. Unfortunately the structure of the NCC and the law is not taught in university. I would recommend reading up on Part A2 of the NCC (including "expert judgement") as it will put you ahead of at least 90% of engineers

 

[Smoulder]

Not quite same but I take BPEQ case below to be requiring 2870 with no room for judgement. Recommendation treated as mandatory requirement. Sounds like footings had no actual problem.

Board v A

An engineer is reprimanded for unsatisfactory professional conduct in preparing slab and footing designs

bpeq.qld.gov.au

 

[Euler07]

Not quite same but I take BPEQ case below to be requiring 2870 with no room for judgement. Recommendation treated as mandatory requirement. Sounds like footings had no actual problem.

The board says that his design was inadequate but the same design on the same soil profile built 5 years ago was adequate? Am I reading that correctly? Regardless, it probably comes down to details and the defense of the engineer. If the engineer's defense was that the design complied with AS2870 but it did not then that's one thing. But if the engineer designed based on first principles and expert judgement then the defense argument may be different.

 

[Smoulder]

I do not know more than that webpage. Remember it from the monthly newsletter. You are right that it is missing details when it is supposed to be educating us but leaves more questions than answers. Maybe 5 year designs were AS2870 for E site and engineer thought overkill. Also not clear who complained and why but it is clear it was still performing okay for class E. So I take it as 2870 being minimum in QLD not just deemed to comply.

 

[LiamJS]

The problem is that engineering is not respected enough even in the minds of people who live in those buildings. They see the time and money spend for a Structural Engineer is a waste. You are building something with a 50-year lifetime cycle and having the cheapest engineering is okay.

This is the definition from the media release from WA government, if you search you can find it, here: "Expert Judgement involves the use of subjective judgement that may not necessarily be supported by any technical calculations. This judgement is based on the experience of an expert using reference material and documents to support a conclusion and is usually applied where the Performance Requirements are difficult to quantify." Yeah the most perfect expert here is the one guess it without spending any time or resource. But it is not someone who requires a soil report and model the soil by springs and consider the soil-structure interaction and decide the cracking level of above members. Nah not attractive. Let the provisions conflict each other. Let the lawyers have the job flow.

 

[Retrograde]

I'm no lawyer, but my understanding is that in Queensland, the NCC is legally binding because it is referenced in and given effect by the Building Act 1975 and the Plumbing and Drainage Act. This is similar for other states and their legislation.

The Australian Standards then have legal standing because they are referenced in the NCC.

On that basis the NCC has precedence over Australian Standards.