Earlier quoted context omitted.
More insulation is double edge sword. I moved into a super-energy-efficient house here in north/east Europe. Heating in winter is damn cheap. But retention works in summer too… so I had to get air conditioner :( And electrical ventilation is a must all year round to get air fresh, keep module at bay ant not loose energy living with open windows. Energy saving in bottom line will be abysmal :(
You're probably missing thermal mass in the house. Comes with bio-sourced insulating material, but usually not with rock/glass whool or polystyrene & the like.
In winter, the house works great to retain heat. But as I learned during construction when I had to prepare for laying flooring, it took a while to heat it up.