Charles Ellicott Commentary Leviticus 27:15

"And if he that sanctified it will redeem his house, then he shall add the fifth part of the money of thy estimation unto it, and it shall be his." — Leviticus 27:15 (ASV)

And if he that sanctified it will redeem his house. —Though the net price thus fixed by the priest is the full amount that anyone else wishing to buy it must pay for the house, yet if its former owner (or, according to the practice common during the Second Temple, his son, wife, or nearest relative) wishes to redeem it, he is to add one-fifth more than the valuation price, just as in the case of animals, and for the same reason: namely, for taking back something he once promised to the Lord. (See Leviticus 27:13.)