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Adding a bathroom to existing consented sleepout in garage - consent advice

Our property currently has a consented sleepout in the garage (consent was done in --- ). We want to add a bathrrom and extend the size of the sleepout into the garage. This would require extending our waste water to the garage. Does this need a full new consent, or is there another way to do it? Can we get an exemption from consent if whoever does the work is a registered builder and plumber etc? We also plan on re-doing the bathrrom within the house which will require plumping to be altered. Can we do one consent for both? We need some advice on CCC consents!