Partial 1031-Rental and Residence on 1 Deed

[Nate Lee]

Hello everyone, new member here.

I need some info on a partial 1031.  My property in Honolulu, Hawaii was originally purchased in the 70's with having 1 house on a large lot.  In the 90's, I built a 2nd house in the back of existing house. The first house is being used as a rental and the 2nd house is my residence.

I am planning to sell my property and would like to do a 1031 on the rental.  According to my CPA, in order to allocate the property he said he will need to know the cost of building 2nd house, my residence.

I don't have all my paperwork or receipts for the cost of the build.  

Are there another way of allocating the property in order to do a partial 1031?

Thank you.