I have studied the order of adjectives. But sometimes we have two adjectives that refer to the same category. Why do we say "a total, compelete idiot" not "a complete, total idiot"? Or "old, delapitaded houses" not "delapidated, old houses"?
2. It is possible that we subconsciously think of 'old house' as being more of a classification than 'dilapidated house'; if that is so, it would explain why the descriptive 'dilapidated' comes first.
Don't forget that there are no absolute 'rules' about the order of adjectives, just observations on what usually happens.