(a) Except as provided by Subsection (b), an attempted waiver of a provision of this chapter is void.
(b) A written contract between an owner and a contractor for improvements to or construction of a single-family residence may provide that the payment required under Section 28.002(a) be made not later than a date that occurs before the 61st day after the date the owner receives the payment request. Notwithstanding Section 28.004(b), an unpaid amount under contract subject to this subsection that allows payment later than the date otherwise required under Section 28.002(a) bears interest at the rate of 1-1/2 percent each month.