The only thing I can think of right now is that you need some color variation for those houses. No ancient city was ever built with every house...houses were built as the city grew. As such, even poor people went through trends and had access to different materials, not to mention fires. I'd add a pattern overlay of something colorful and set that to multiply or one of the burn modes then turn down the opacity. You could get away with just a clouds overlay but that leaves you with just brown and dark brown...color gives you some reds and oranges etc.