Foundation and front of building unchanged (5)
I believe the answer is:
basis
'foundation' is the definition.
(I know that foundation can be written as basis)
'front of building unchanged' is the wordplay.
'front of' suggests taking the first letters (the letter at the front of the word).
'unchanged' becomes 'as is' (as things currently are).
The initial letter of 'building' is 'b'.
'b'+'asis'='BASIS'
'and' is the link.
(Other definitions for basis that I've seen before include "Principle on which a theory is founded" , "grounds" , "First principle" , "Foundation or support, or a main principle" , "Underlying support for a theory" .)