Complex sentence: Many of these houses had amenities like running water, and their wood construction made these houses susceptible to frequent fires, though new brick-and-stone houses erected in the early 1900s were built with indoor plumbing and less prone to fire.
Split into simpler sentences: Many of these houses had amenities like running water, and their wood construction made these houses susceptible to fires. New brick-and-stone houses erected in the early 1900s were built with indoor plumbing and less prone to fire.