The LPG gas leak igniting caused the explosion - which was so big it was heard streets away.
Auckland Council is set to launch an investigation into whether modifications to the backyard sleepout had the necessary consents.
A spokeswoman said officials were still waiting to get access to the property.
"Once we've have access we will be able to see if any activities have taken occurred that were not consented for. Until we gain access, there isn't anything further we can provide," said the spokeswoman.
Auckland Fire and Emergency Operational Support Facebook page showed the extent of the blast saying it was so violent the roof was flung into a neighbouring garden and the back wall hurled 30m against a nearby house.
Those who attended the blaze were amazed two people managed to survive the violent blast and fierce fire that erupted at the suburban property.
They said there was little left after the explosion which could be heard across the suburb with all the walls blowing out and the roof flying through the air and into a neighbour's property.
Coffin said it was a timely reminder for people to regularly check and maintain any gas fittings and connections in homes.
He said it was important to turn gas cylinders off when finished using it.
If you smelt gas it was important to get out of the house and call 111.