> For instance old wood double hung sash windows require a weight box to work. Those boxes can’t really be insulated. In Denmark, this was solved by adding a s

> For instance old wood double hung sash windows require a weight box to work. Those boxes can’t really be insulated. In Denmark, this was solved by adding a second, modern window on the inside. The outside kept the same look, and it is even more insulating than a single modern window. Is it a bit clunky to have to open two windows ? Sure. But it is better than not having insulated windows, or ruining the appearance of cities.