Attheendoftwentyyears - He employed seven years and a half in building the temple, and twelve and a half, or thirteen, in building his own house. - Compare this with 1 Kings 7:1.
Albert Barnes
Notes on the Whole Bible
Compare the references to 1Kings.
SDA Bible Commentary (limited)
Volume 1-7
1. It came to pass.Chapter 8 deals with Solomon’s building activities, his offerings, priestly appointments, and ships at Ezion-geber. The parallel, though not identical, record of Solomon’s enterprises is found in Kings 9:10-28.
Twenty years. Solomon began to build the Temple in his fourth year; the task occupied 7 years (1 Kings 6:1, 38). The following 13 years Solomon devoted to the task of the construction of his palace (1 Kings 7:1).