simon
New Member
Posts: 19
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Post by simon on Nov 20, 2018 11:12:12 GMT 12
Hi,
Can anyone comment on the minimum occupancy required for a dwelling designed within AS/NZS1547:2012. I realise TP58 has a 4 occupancy minimum, but for a design in 1547 what would the minimum occupancy be for a 1 bedroom, small dwelling. Any experiences with councils on this, whether they have a requirement separate to 1547 for minimum. I would think at least 3 occupancy allowing for peak occupancy but is this reasonable if there is no further accomodation space apart from pitching a tent?
Simon
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Post by techworks on Nov 20, 2018 12:23:47 GMT 12
1547 TABLE J1 is a "guideline" based on a 24 yr retention time and 5 yr pumpout. (see J 3.1 & 3.2)
If you actually calculate min tank vol based on sludge/scum buildup using the two formulae in the BOPRC OSET Plan appendix you get the following tank volumes:
occ form 1 form 2
5 2944 3300
6 3533 3960
7 4122 4620
8 4710 5280
9 5299 5940
10 5888 6600
so table J1 tank sizes are undersized once you get past 7 people.
If you go by the foreword in 1547 which states "is stressed that a risk management approach entails looking more at the risk of a particular situation than the numerical values which are put forward in this document as guidance", then there is no reason to limit a design to the minimum tank size in table J1. Do a risk assessment, and calculate an appropriate tank size from first principles based on desired retention time and pumpout cycle.
This is particularly relevant for secondary dwelling that may only have a max occupancy of 1-2 persons.
However, in TP 58/GD06 an absolute minimum tanks size of 4500l is specified. The proposed change 14 for the BOPRC OSET plan is also proposing the same minimum tank size! Both these RC's are trying to build in redundancy to future expansion which I believe is exceeding their authority!
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