Our energy assessor specified R5.0 ceiling insulation for a climate zone 7 build, but the builder insists R4.0 is enough because the roof has sarking. Who is right?
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Ask your own, freeCorrection, 26 September 2026. An earlier version of this answer settled the question from Table 13.2.3h of the ABCB Housing Provisions. That table does not apply in Tasmania. This version replaces it.
Neither side can win this argument by quoting the national zone 7 table, because in Tasmania it is not the law. The Tasmanian schedule to the Housing Provisions replaces the whole of Section 13, the energy efficiency section that contains Table 13.2.3h, with Part 3.12 of BCA 2019. [1] NCC 2022 Volume Two does the same one level up: in Tasmania, Part H6 is replaced with Part 2.6 of BCA 2019 Amendment 1. [2] [3]
What that means for this dispute.
- Table 13.2.3h, its R3.5 to R5.0 range and its roof ventilation notes do not decide a Tasmanian ceiling. An argument built on them, from either side, is built on the wrong provision.
- The requirement that governs is in BCA 2019 Part 3.12. [1]
- We have not reproduced the BCA 2019 figures here. We have not verified them against the source, and a ceiling R-value is not a number to guess.
How to settle it. Put the question back to both of them in BCA 2019 terms:
- Ask the assessor which BCA 2019 compliance pathway the R5.0 comes from, and the clause or table that produced it. If it came out of an energy rating rather than a table, the rating is the source, and the question becomes whether the rating was done on the Tasmanian basis.
- Ask the builder to point to the BCA 2019 Part 3.12 provision that lets sarking bring the ceiling down to R4.0. "The roof has sarking" is not an answer until it is tied to a clause.
- Take both answers to your building surveyor before the insulation is ordered.
Edition note. Tasmania is on NCC 2022 Amendment 2 until 30 April 2027, with the latest edition applying from 1 May 2027. The Tasmanian schedule to the NCC 2025 Housing Provisions, as published, carries the same replacement of Section 13 with BCA 2019 Part 3.12, and NCC 2025 Volume Two carries the same replacement of Part H6. [4] [5] On the published text, the move to NCC 2025 does not bring the national energy tables into Tasmania. Confirm with CBOS before relying on that for a project approved after 1 May 2027.
- 1ABCB Housing Provisions Standard (NCC 2022)Tasmania schedule, TAS Parts 13.1 to 13.7 · p. 547
- 2NCC 2022 Volume TwoTasmania schedule, TAS Part H6 Energy efficiency · p. 275
- 3ABCB Housing Provisions Standard (NCC 2022)Tasmania schedule, referenced documents: BCA 2019 Amendment 1 (TAS Section 13, TAS Part H6) · p. 551
- 4ABCB Housing Provisions Standard (NCC 2025)Tasmania schedule, TAS Parts 13.1 to 13.7 · p. 563
- 5NCC 2025 Volume TwoTasmania schedule, TAS Part H6 Energy efficiency · p. 293
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This answer is for professional reference only and does not replace a registered building surveyor or certifier. The operative edition of the NCC differs by jurisdiction and changes over time. Verify against the current code for your jurisdiction before relying on it.