the increase in the basis of such property which would (but for this subsection) result from such expenditure shall be reduced by the amount of the credit so allowed. (i) Processing fees Any State may impose a fee for the processing of applications for the certification of any rehabilitation under this section provided that the amount of such fee is used only to defray expenses associated with the processing of such applications. (j) Denial of double benefit No credit shall be allowed under this section for any amount for which credit is allowed under section 47. (k) Regulations The Secretary shall prescribe such regulations as may be appropriate to carry out the purposes of this section, including regulations where less than all of a building is used as a principal residence and where more than 1 taxpayer use the same dwelling unit as their principal residence. . (b) Conforming amendments (1) Subsection (a) of section 1016 of such Code is amended by striking and at the end of paragraph (36), by striking the period at the end of paragraph (37) and inserting , and , and by adding at the end the following new item: (38) to the extent provided in section 25E(h). . (2) The table of sections for subpart A of part IV of subchapter A of chapter 1 of such Code is amended by inserting after the item relating to section 25D the following new item: Sec. 25E. Rehabilitation of historic principal residences. . (c) Effective date The amendments made by this section shall apply with respect to rehabilitations the physical work on which begins after the date of enactment of this Act.