Discussion»Questions»Home and Garden» What causes the interior of a house to always be SO cold in the wintertime, much colder than the temperature outside,
It is the key but the reason is that when the temp drops at night it takes much of the night for the indoor temp to drop when you have good insulation. The reserve is also true. So just because the outdoor temp rises 20 degrees in seven hours has little to do with the temp in your home rising. Raising windows will help. The above statement about a well insulated home is true generally but is not the answer to your question.
Because you live somewhere where it doesn't get very cold in the winter, so houses are built with staying cool in summer in mind. If houses were like that in Chicago, we'd all be dead.
It's in the construction. Either it wasn't insulated and draft sealed well enough, or the type of insulation used was a blown in kind and overtime loose fill insulation settles and leaves gaps at the top and the compressed loose fill has less air space and it lowers the R value of it. Could also be the acrylic caulk used to draft seal has started to deteriorate.