He's Taking Care of Her
Consider it a primal response to a man providing shelter; kind of like the males of some bird species who make a nest in order to attract a female. Some wiring in a woman's brain may help her see the physical labor involved in the remodel as a kind of unspoken mating ritual. She loves her house, and he knows how to take care of it, which feels like taking care of her. He's at home in the physical world of furnaces and hot-water heaters, which makes her feel protected and safe.