This isn't the usual "do I need building consent" question.
Just a little story about what's happened so far with replacing my earthquake damaged deck - where consent was definitely needed.
The timber deck is replacing a failed concrete deck.  The concrete deck weighs approx 12 tonnes, but the existing footings didn't fail in the EQs.  It's being replaced because about 5 tonnes of chimney fell on it in one piece, from about 3m above, landing bang smack in the middle and shattered it.  A numbskull from EQC thought that they could glue it back together - but that's another story. The replacement deck will be a fraction of the weight of the old one, and actually with one more footing holding it up - we weren't ever going to cheap out.
Meanwhile, as I've been writing cheques, Christchurch City Council has brought in a consent exemption to "aid the EQ repair progess", allowing construction of a deck up to 3m high, without consent.  Alas - I can't go back - and anyway the maximum fall from the deck is about 3.2 metres, so wouldn't be exempt anyway, unless I dropped it 200mm.
OK - so it's "restricted work" and needs design and building consent.  This done, by registered designer, to NZS 3604, consent application lodged.
One month later, council sends an RFI (request for information) for the application, in particular the footings for the timber deck, where they want a geotechnical survey "shallow load bearing test" done, and an engineering design based on the test results. This surprised the builder and the designer and me, though we always knew the footings need to be deeper than 600mm, as some are in loose uncompacted fill, so we planned to dig them to 1200mm.  
Geotech arranged, then passed on to engineer, back to designer, back to council.  Consent issued 4 months later, 3 council inspections required for footings etc, plus 3 inspections by the engineer and one by the geotech.
After all this the engineer has (at great cost, supported by pages of calculations) designed footings 1200mm deep.  My builder isn't an idiot.
Approximate additional unanticipated compliance cost so far is going to be about $6,000 - for a 30M2 deck, and in the end it's really $6000 compliance cost to dig 5 holes in the ground.  The additional "actual work" to meet all this will be close to nil.
Having a deck collapse would be a pretty nasty thing to happen.  But still - this is all just absolutely nuts.