Depending on the program, a single close construction to permanent loan combines the construction loan and the permanent mortgage into one closing. You close once, the construction phase happens, and the loan converts into permanent financing under the lender's terms once the home is complete and conditions are met. It does not convert automatically. It converts when the lender confirms the completion conditions in your loan agreement have been satisfied.
A two closing structure separates these into distinct events: one closing for the construction loan, a second closing later for the permanent mortgage once the home is done. Two separate closings may offer different options than a single close program, and the right fit depends on your lender, your goals and the specific program.
Neither structure is automatically better. The way to know which fits your situation is to compare the actual Loan Estimates side by side, not just a general description of "single close" or "two closings." Fees, terms and conditions vary by lender and by program.