The most common and most likely answer to this crossword clue is the 14 letter word SUPERSTRUCTURE
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Buddy explains!
The straight part
We know that "Part of building above foundations" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of building above foundations = superstructure.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SUPERSTRUCTURE mean?
SUPERSTRUCTURE noun- Any structure built above the top full deck (FM 55-501).
- Any material structure or edifice built on something else; that which is raised on a foundation or basis.
- (sometimes figurative) All that part of a building above the basement.
- The sleepers and fastenings, in distinction from the roadbed.
- The social sphere of ideology which includes religion, art, politics, law and all traditional values.