s 525 Writing off writing-down allowances
(1) If a writing-down allowance is made in respect of qualifying expenditure attributable to a dwelling-house, the amount of the allowance is written off at the end of the chargeable period for which the allowance is made. (2) If a balancing event occurs at the end of a chargeable period, the amount written off under subsection (1) is to be taken into account in calculating the residue of qualifying expenditure immediately before the event to determine what balancing adjustment (if any) is to be made.