The calculation underpinning the estimated €1 billion net fiscal space is illustrated in Table A2 on page 27 of the Summer Economic Statement. The discretionary measures as detailed in item 8 include the carry forward impact of tax measures from budget 2016.
By definition, expenditure measures are included in the base for the calculation of the following year's fiscal space.
I should point out that the exact impacts of carryover will be reviewed as part of the normal Budgetary process, as there are a lot of moving parts to be considered, such as economic growth, take up of various schemes and specific tax relevant factors, which could impact on the expected return from the measures.