Apartment complex renovation

[William Simpson]

168 unit apartments in Atlanta, Georgia. 

Half off the property is occupied with property coverage that only covers occupied buildings  

Other half of the property is under renovation and has builders risk policy(no new buildings, no structural changes.) this policy obviously only covers vacant buildings. 

Builders risk coverage is significantly higher cost than property coverage. Do I need builders risk, or can I just extend my property coverage to cover all buildings and maybe have an endorsement for renovation(if they do that?) 

Has to be a cheaper way, ideas?