The building is not getting any worse (6)
I believe the answer is:
stable
'the building' is the definition.
(stable is a kind of building)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for stable that I've seen before include "String may be kept in this" , "far from bats?" , "Equine housing" , "providing accommodation for Arabs, perhaps" , "Secure - fast - horses" .)