Insulation slows heat transfer down, it doesn't create heat. In a well insulated house you need to do the reverse of what you do in winter. For example, you wouldn't keep a door open in winter letting the warm air out - so in summer during a heat wave, don't open a door and let the warm air in. Close curtains to lessen thermal gain, open windows at night to let cool air in only.Might as well go the whole hog and have a panic room too. Dont get carried away is my advice, no point building something you cannot afford to live in. Insulation is great until the house is to too hot to sleep in during the summer. A great many new houses are no good for anybody coming home dirty too, need a tradesmans entrance