Leviticus 27:15

And if he that sanctifieth it will redeem his house,.... An house set apart for holy uses might be redeemed, either by another paying the price set upon it by the priest, or by the original owner of it paying a fifth part more; and this was the case, whether of houses in walled cities or in villages: so Maimonides says,

"he that sanctifies his house, whether it be one of those in walled cities, or of those in villages, it may be always redeemed; he that redeems one out of the hand of holiness (or which has been sanctified), if it is a house in a walled city, and remains in the possession of the redeemer twelve months, it is absolutely his; but if it is a house in the villages, and the jubilee comes, and it is in the possession of the redeemer, it returns to its owner in the jubilee b:''

but if the owner of it had a mind to redeem it after he had devoted it,

then he shall add the fifth [part] of the money of thy estimation unto it, and it shall be his; that is, he was to give a fifth part more for the house than it was valued at by the priest, or than another might have it for; the reason of which was, to make men careful how they sanctified or vowed their houses or goods, and that it might be certain that the full value was given for it, the worth of which the priest might not know so well as the owner, and the latter, being willing to give the price set by the former, might give suspicion of it; wherefore, in order to have the full price of it with certainty, and to set an high value on things devoted, the owner was to give a fifth part more than the estimation of it: thus, for instance, if an house thus devoted was valued by the priest at the price of an hundred pounds, the owner was obliged, if he would redeem it, to give an hundred twenty pounds.

b Hilchot Eracin, c. 5. sect. 3, 4.