Moisture is the enemy of old buildings, so it makes sense to first tackle the things that can affect moisture the most. Leaky roofs, broken, missing, or clogged gutters, and poor grading can all cause moisture to run down walls or against the foundations, letting water into walls and basements. In extreme cases, you may need a roof replacement or considerable reconstruction work, which is costly, but should last for decades. Even if they don't need replacing, they'll almost certainly need cleaning, and you can also install gutter guards to prevent further debris accumulation. So, regrading or a French drain may be necessary to prevent further moisture issues.