my house is 31 ft x 24 ft one story. i would like to take off old roof and put a second floor on. the building inspector says that the exisiting joists 2x5's 16" on center my not be enough support. i need to know if i can sister more 2x5 next to the exisiting ones. the joist run from side to side spaning 24 ft. will sistering joists support 30 pds per inch? i plan on reinforcing everything with beams running vertical to joists.