The way to start work on a house (3)
I believe the answer is:
how
'the way to' is the definition.
(ie how to do something)
'start work on a house' is the wordplay.
'start' suggests taking the first letters.
'on' says to put letters next to each other.
'a house' becomes 'ho' (abbreviation for house).
The first letter of 'work' is 'w'.
'w' put after 'ho' is 'HOW'.
(Other definitions for how that I've seen before include "In what manner or method?" , "See 16" , "In what way?" , "By what means?" , "Who (anag.)" .)