Start to build two outhouses to conceal entrance to duplex, creating carnage (9)
I believe the answer is:
bloodshed
'carnage' is the definition.
(I know that bloodshed is a type of carnage)
'start to build two outhouses to conceal entrance to duplex' is the wordplay.
'two outhouses' means two replacements for 'outhouse'.
'start to' indicates taking the first letters.
'outhouse' becomes 'loo' (I am not sure about this - if you are sure you should believe this answer much more).
'outhouse' becomes 'shed' (a shed is an outside building).
'to conceal' is an insertion indicator.
'entrance to' says to take the initial letters.
The initial letter of 'build' is 'b'.
The first letter of 'duplex' is 'd'.
'loo'+'shed'='looshed'
'looshed' enclosing 'd' is 'loodshed'.
'b'+'loodshed'='BLOODSHED'
'creating' acts as a link.
Can you help me to learn more?
(Other definitions for bloodshed that I've seen before include "The killing or wounding of people, very gory" , "Carnage" , "Indiscriminate slaughter" .)