Kommentar zu Wajikra 27:13

ואם גאל יגאלנה BUT IF HE WILL AT ALL REDEEM IT [THEN HE SHALL ADD A FIFTH …] — In respect to the owner Scripture is more stringent by requiring him to pay an additional fifth. And similarly in the case of one who dedicates a house to the Sanctuary (vv. 14, 15) and so, too, in the case of one who dedicates his field (v. 19), and similarly in the case of redeeming מעשר שני, “the Second Tithe”, the owner must add a fifth to their real value when redeeming them; but no other person has to do this (Sifra, Bechukotai, Chapter 10 7; Arakhin 25a).

ויסף חמישתו, “he shall add a fifth part thereof;” actually 25%, so that when combined, the addition is a fifth of the total. (Talmud tractate Baba Metzia folio 57) The same ratio for penalties applies to houses that are ancestral properties or to ancestrally owned fields. The same ratio applies also when the second tithe has to be redeemed, as the owner cannot transport the original all the way to Jerusalem. The background to this legislation which applies only to the original owner, not someone who has acquired it, is that an original owner may use sanctifying this property by arguing that seeing it is all his anyway, he may thereby avoid leaving those parts of the harvest which the Torah wanted him to leave for the poor and the orphaned. If, however, the owner sanctified something, no part of which was intended by the Torah as a tithe (tax) that he had to give away anyway, Shmuel in the Talmud ruled that he can redeem the whole for an addition of the smallest coin of the realm.(Baba Metzia 57)