354. Underwater Mortgage: The obligation to add one-fifth when redeeming a house

If a person consecrates a house to the Temple and he or his heirs later wish to redeem it, the kohein appraises it. The person redeeming it then adds one-fifth to that amount in order to redeem it. (“One-fifth” actually means 25% - i.e., it’s one-fifth of the total amount. For example, if something is worth $100, he adds $25. $25 is one-fifth of $125, which is the total amount.)

The reason for this mitzvah is that God is merciful – He gave us a way to redeem a consecrated house if the one who donated it should later regret it. However, people should not be too hasty to consecrate things. The fact that one must add an extra fifth when redeeming a house should give a person pause. He should take the time to consider whether he truly wishes to give this house to the Temple based on the fact that reversing his action is costly.

As with other things that one might consecrate towards Temple upkeep, dedicating a house works in all times and places but it ought not be done in the absence of the Temple. If someone should consecrate a house nowadays, the value he pledged would be forfeit (or, less severely, he could exchange it for some object, which must be destroyed). In any event, the part where the kohein appraises the value of the house for redemption, which is the crux of or current mitzvah, is only in effect at a time when the Jubilee year is observed.

This mitzvah is discussed in the Talmud in the ninth and final chapter of tractate Arachin. It is codified in the Mishneh Torah in the fifth chapter of Hilchos Arachin and is #116 of the 248 positive mitzvos in the Rambam’s Sefer HaMitzvos.