And now I understand everything.
Well not so much the triple-glazed windows as I don't think we have too m any of those here, I have previously lived in houses that were hotboxes in summer (and this was when it was nice balmly tropical weather and not even summer proper).
Did you take our summer weather and add it to your own? That temperature is slightly obscene.
Adelaide always gets Perth weather as that's the way the wind blows. So we know what we're going to get a couple day prior, unless a front pushes up from the south.