One thing to know about comparing the cost of building a basement versus adding on a second-story is it all typically depends on the price of lumber. Building a second story usually requires much more lumber. When lumber prices were at an all-time high during the lumber shortage of 2021, the cost of adding on a second story was terrifyingly more expensive than building a basement in most cases. However, before the lumber shortage, it was generally accepted that building up was the cheaper route. So as current lumber prices continue to drop, the price to build up should be getting closer to the price of building down.