Mr Ide said the other two fires were at Clyde and Galloway, both near Alexandra. One was caused when ashes were put in a wheelie bin.
''Quite simply, you've got to put them into a metal bucket or drum, with a lid on it to exclude the oxygen, or cool the ashes straight away with water.''
Twenty-four firefighters from Queenstown and Frankton tackled Sunday's blaze.
It took hold in one house about 1.15pm, before spreading to the other.
Two people escaped from the second property without injury.
No-one from the other house was at home.
Mr Ide said everyone should be more cautious at this time of the year.
People should also be wary of overloading electrical multi- boxes.
And they should not attempt to extinguish a fire themselves, unless trained.
''The advice is always to get out of the property and call us as soon as possible.''
Mr Ide said the investigation was concluded and insurance assessors, who attended yesterday afternoon, agreed on the cause.