NCC Insulation Requirements: R-Values for Roofs, Walls and Floors by Climate Zone (2025 Guide)
The minimum insulation R-value for a house ceiling, wall or floor is read from the climate-zone tables in Part 13.2 of the ABCB Housing Provisions. This guide gives the headline NCC 2025 figures for the common cases in all eight zones, plus the thermal bridging, reflective foil, solar absorptance, edge-reduction and condensation rules around them.
NCC insulation requirements for a house are not one number. The minimum R-value for a ceiling, wall or floor is read from tables in Part 13.2 of the ABCB Housing Provisions, and every table is indexed by climate zone, then by roof or wall colour, roof ventilation, reflective foil, eaves overhang, wall height or subfloor height. The same ceiling can need R3.0 in Perth, R4.0 in Melbourne and R5.0 in Canberra. This guide sets out where those figures come from in NCC 2025, the headline minimums for the common cases in each zone, and the rules around the tables.
The short answer
On the elemental Deemed-to-Satisfy route, clause 13.2.3 sends roofs and ceilings to Tables 13.2.3a to 13.2.3r, clause 13.2.5 sends external walls to Tables 13.2.5a to 13.2.5o, and clause 13.2.6 sends floors to Tables 13.2.6a to 13.2.6h. For a pitched roof with a flat ceiling, standard ventilation, no reflective foil and no insulation under the roof cladding, the ceiling minimum runs from R3.0 in climate zone 5 and R3.5 in zone 4, through R4.0 in zone 6, to R5.0 for a light-coloured roof in zone 7. A brick veneer wall with 450 to 600 mm eaves needs R1.5 in zones 2 and 5, R2.0 in zone 4 and R2.5 in zones 6 and 7; a lightweight wall adds R0.3 in zones 2 and 4 to 7. A suspended floor over an enclosed subfloor needs R1.5 in zone 5, R2.0 in zone 6 and R2.5 in zones 7 and 8, and slabs need edge and under-slab insulation from zone 6.
The tables are for the elemental route only; a house rated with NatHERS software carries whatever the assessor needs for 7 stars. The clause text of 13.2.3, 13.2.5 and 13.2.6 is the same in NCC 2025 as in NCC 2022. New South Wales, Queensland and South Australia stay on NCC 2022 until 1 May 2027; Victoria, Tasmania, Western Australia and the ACT moved to NCC 2025 on 1 May 2026; the Northern Territory stays on 2022. See the state adoption dates post.
1. Two routes: NatHERS or the elemental tables
Volume Two clause H6D2(1) gives two Deemed-to-Satisfy ways to meet Performance Requirement H6P1. Option (a) is Specification 42: a house energy rating of at least 7 stars (S42C2(1)(a)) with separate heating and cooling load limits, dropping to 6.5 or 6 stars in climate zones 1 and 2 for a house with a qualifying covered outdoor living area. Option (b) is the elemental route: Parts 13.2 (fabric), 13.3 (glazing and shading), 13.4 (sealing) and 13.5 (ceiling fans) of the Housing Provisions.
The R-value tables belong to option (b) only, but S42C4(1) says a NatHERS-rated house must still comply with 13.2.2 (installation), 13.2.3(7) and 13.2.5(5) (thermal breaks), 13.2.3(5) (lost ceiling area, unless the software has compensated), 13.2.6(4), (5)(a)(i), (5)(b)(i) and (6) (slab edge insulation) and Part 13.4. Thermal breaks and slab-edge insulation therefore apply to every house; under-slab insulation is elemental-route only. Part 13.2 covers Class 1 buildings and Class 10a buildings with a conditioned space (13.2.1(1)).
2. Total R-value versus added insulation R-value
The main tables give the minimum R-value of the insulation to be added, meaning the product's rated value under AS/NZS 4859.1 (13.2.2(1)). Total R-value is the resistance of the whole assembly, including cladding, air spaces, linings and surface air films, and appears where the code wants a calculated whole-of-element figure: the thermal bridging tables for metal frames and the sandwich panel roof table 13.2.3x. The Northern Territory's note under its 13.2.3 puts it simply: the Total R-value required is the Total R-value of the basic element plus the R-value of any added insulation. A batt sold as R4.0 satisfies a cell that says 4.0; a steel-framed ceiling that must reach a Total R-value of 2.95 in Table 13.2.3s needs a calculation.
3. Roof and ceiling minimums by climate zone (13.2.3)
Clause 13.2.3(1) allocates two tables to each zone, one for a pitched roof with a horizontal ceiling and one for a flat, skillion or cathedral roof; zone 1 gets four because it splits single storey from two or more. Rows are roof ventilation (vented or standard), reflective insulation under the roof and any under-roof insulation; columns are bands of roof solar absorptance (SA). The zone comes first, and the climate zones guide covers how to find it. Reading the row for a standard-ventilated roof space, no reflective insulation and no under-roof insulation:
Zone 1 (Table 13.2.3a, single storey): R3.5 for a roof of SA 0.23 or less. Every darker band in that row is X, so a mid-toned roof in Darwin needs foil or under-roof insulation before a ceiling figure exists. With foil the row reads R1.5, R2.0, R2.5, R4.0 to SA 0.53, then X.
Zone 2 (13.2.3c): R3.0 to SA 0.32, R3.5 to 0.42, R4.0 to 0.64. With foil, R2.5 for any colour.
Zone 3 (13.2.3d): R3.5 at SA 0.23 or less, R4.0 to 0.32, R5.0 to 0.42, X beyond.
Zone 4 (13.2.3e): R3.5 for any SA to 0.64. Zone 5 (13.2.3f): R3.0. Zone 6 (13.2.3g): R4.0 for any SA from 0.23 to 0.96.
Zone 7 (13.2.3h): R5.0 at SA 0.23 or less, R4.5 to 0.42, R4.0 to 0.64, R3.5 for the darkest roofs.
Zone 8 (13.2.3i): R4.5 at SA 0.23 or less, R4.0 to 0.42, R3.5 to 0.64, R3.0 for the darkest roofs.
Note the reversal: in the warm zones a darker roof pushes the ceiling value up or off the table, while in zones 7 and 8 it lets the value come down. Under 13.2.3(10) a roof in climate zones 1 to 5 must have a solar absorptance of not more than 0.64, which is why no warm-zone table has a column beyond it.
4. External wall minimums by climate zone (13.2.5)
Clause 13.2.5(1) covers walls that are not lightweight (concrete block, masonry veneer, masonry cavity) and 13.2.5(2) covers lightweight walls, which the note describes as a framed wall with no high thermal mass cladding or lining, typically weatherboard, fibre cement, metal or autoclaved aerated concrete. Each table is indexed by wall solar absorptance, eaves overhang and wall height. For a wall of SA 0.5 to 0.7 (typical face brick and mid-tone cladding), an overhang of 450 to 600 mm and a wall height up to 2.4 m:
Zone 2: masonry veneer R1.5 (13.2.5c); lightweight R1.8, since 13.2.5(2)(b) uses the same table with R0.3 added.
Zone 3: any non-lightweight wall R1.5 (13.2.5e, a one-cell table); lightweight R1.5 to SA 0.6 and R2.0 above it (13.2.5f).
Zone 4: veneer R2.0 (13.2.5g), lightweight R2.3. Zone 5: veneer R1.5 (13.2.5i), lightweight R1.8.
Zone 6: veneer R2.5 (13.2.5k), lightweight R2.8. Zone 7: veneer R2.5 (13.2.5m), lightweight R2.8.
Zone 8: only a lightweight table exists (13.2.5o), reading X at 2.4 m and R2.7 at 2.4 to 2.7 m. Masonry veneer is not listed in 13.2.5(1) for zone 8, so an alpine brick veneer house is a NatHERS or Performance Solution job.
Zone 1: Tables 13.2.5a and 13.2.5b are built around shading, and a lightweight wall in this case needs reflective insulation only.
Zone 6 has a trap: for a light-coloured veneer (SA 0.35 or less) with 450 to 600 mm eaves, every wall height in Table 13.2.5k reads X, and the R2.5 answer only appears for walls darker than SA 0.5. Under 13.2.5(3) the outer surface of a wall in zones 1 to 5 must have a solar absorptance of not more than 0.7. Western Australia allows a zone 6 site to be treated as zone 5 for Parts 13.2 and 13.3 only (WA 13.2.1(4)), with condensation management unaffected.
5. Floors and slabs (13.2.6)
A suspended floor over an unenclosed space needs the value in Table 13.2.6a: R2.0 in zones 1 and 2, R1.5 in zone 3, X in zones 4 and 5, and for zones 6 to 8 a single merged entry of R4.0, or R3.5 with a reflective airspace. Over an enclosed subfloor, 13.2.6(2) asks for subfloor wall insulation of R1.5 in zone 1 and R0.5 for a wall up to 600 mm in zones 2 and 3 (Tables 13.2.6b, 13.2.6c). From zone 4 the tables trade floor insulation against subfloor wall insulation and foil facing down: for a subfloor wall up to 600 mm, no foil and no wall insulation, the floor needs R1.0 with an R0.5 wall in zone 4, R1.5 in zone 5, R2.0 in zone 6 and R2.5 in zones 7 and 8.
Under 13.2.6(5) a concrete slab-on-ground, other than a waffle pod slab, needs at least R0.64 around the vertical edge and R0.64 under the slab in zones 6 and 7, and R1.0 edge with R2.0 underneath in zone 8. Any slab with in-slab or in-screed heating or cooling needs R1.0 around its edge in every zone (13.2.6(4)), except a system used solely in a bathroom or the like.
6. Thermal bridging in metal frames
The table values assume a timber frame. For a metal-framed pitched roof with a flat ceiling, 13.2.3(3)(a) offers four options: achieve the Total R-value in Table 13.2.3s (a table value of R4.0 becomes 2.95); add R0.5 between the ceiling frames; add a continuous layer of at least R0.13 above or below the joists; or stack two layers with the top one, at least R0.5, laid across the joists. Skillion and cathedral roofs use Table 13.2.3t or 13.2.3u.
Walls follow 13.2.5(4): the Total R-value in Tables 13.2.5p to 13.2.5r calculated to AS/NZS 4859.2, or the options in 13.2.5s to 13.2.5u. Table 13.2.5t for lightweight steel-framed walls offers a 20 mm reflective airspace outside the frame, or R0.5 more between the frames (up to R1.5), or a continuous layer of at least R0.30 (above R1.5). Separately, 13.2.5(5) requires a thermal break of at least R0.2 at every point of contact between cladding and a metal frame where the wall has no lining, or a lining fixed directly to the frame, and is clad with weatherboards, fibre cement or metal sheeting fixed to the frame; the note deems 12 mm expanded polystyrene or 20 mm timber to achieve R0.2. Clause 13.2.3(7) is the roof equivalent for metal sheeting fixed directly to metal purlins, rafters or battens.
7. Reflective insulation rules
Where reflective insulation is used to reach a roof table value, 13.2.3(2) requires a surface emittance of not more than 0.05, an adjacent roof space of at least 20 mm and, in climate zones 3 to 8, that it faces downward. Clause 13.2.2(2) adds the necessary airspace, close fitting at penetrations, support by framing and sheets overlapped at least 150 mm or taped. The 13.2.5 note adds that foils outside the primary insulation layer may be subject to the vapour permeance limits of 10.8.1(2).
8. The R3.0 edge reduction and the lost-area rule
Under 13.2.3(6), required ceiling insulation of more than R3.0 and up to R4.5 may be reduced to R3.0 within 450 mm of an external wall; above R4.5 the same reduction is allowed provided all other ceiling insulation is increased by R0.5. That is what lets batts taper at a low eave. Under 13.2.3(5), where ceiling insulation area is lost for operational or safety reasons, Table 13.2.3w sets the compensation: losing 0.5 to 1.0 per cent of the area takes a required R4.0 to R4.7, 1.0 to 1.5 per cent takes it to R5.2, and past 2.5 per cent there is no compensating value for R4.0. Roof lights do not trigger the rule.
9. Where insulation meets condensation (Part 10.8)
Clause 13.2.3(4) makes the link: where 10.8.3(1) applies, meaning a roof in climate zones 6, 7 or 8 with the insulation on the ceiling rather than the roof plane, any continuous insulation placed above the primary insulation layer to mitigate thermal bridging must have a vapour permeance at least equal to the primary layer. That roof must also keep a ventilated roof space of at least 18 mm above the insulation, so a board over the joists cannot close it. On the wall side, 10.8.1 governs any control layer outside the insulation. The climate zones guide sets out the Table 10.8.1 values and the zone 6 to 8 cavity rule.
10. What changed from NCC 2022, and the Northern Territory exception
Comparing the NCC 2022 text of 13.2.3, 13.2.5 and 13.2.6 with NCC 2025 Volume Two v1.2, the clause wording is the same: the table allocations, the solar absorptance caps, the R0.3 lightweight addition, the thermal bridging options, the R3.0 edge reduction and the slab figures. What changed in the cooler zones is Part 10.8, which those clauses defer to.
The Northern Territory replaces Part 13.2 with its own provisions. NT 13.2.3 asks a roof to achieve a Total R-value of 2.7, reduced to 2.2 where the roof solar absorptance is not more than 0.55 or the roof space is ventilated to stated opening areas, and NT Tables 13.2.3a to 13.2.3c convert that to added insulation. NT 13.2.5 asks each part of an external wall to reach a Total R-value of 1.9, or 1.4 on a slab-on-ground, or to be shaded heavy masonry. NT H6D2 sets a 5-star rating rather than 7.
Checklist
Confirm the route first: NatHERS 7 stars (S42C2) or the elemental Part 13.2 tables, and which NCC edition applies in the state.
Record the NCC climate zone from the ABCB map.
Fix the roof SA (zones 1 to 5: not more than 0.64) and wall SA (not more than 0.7), then read the ceiling, wall and floor values for the actual roof type, ventilation, foil, eaves, wall height and subfloor height; note any X, and add R0.3 for lightweight walls in zones 2 and 4 to 7.
For steel frames, add the thermal bridging step (13.2.3(3), 13.2.5(4), 13.2.6(3)) and the R0.2 thermal break where cladding or roofing is fixed directly to the frame.
Count downlights and fans against Table 13.2.3w, note the R3.0 edge reduction in 13.2.3(6), and apply 13.2.6(5) slab insulation in zones 6 to 8.
In zones 6 to 8, check continuous insulation and foils against 10.8.1 and 10.8.3 before they go on the section.
Check it against the source
AEC Assistant searches the full text of NCC 2025 and NCC 2022 and Australia-wide planning information, resolves the edition in force for the state you are working in, and returns the clause that applies to your project with the source alongside it. Paid plans add deeper knowledge of the standards the code references. Try it free. No credit card.
Sources: ABCB Housing Provisions 2025 (NCC 2025 Volume Two v1.2) clauses 13.1.1, 13.1.2, 13.2.1 to 13.2.7 and Tables 13.2.3a to 13.2.3x, 13.2.5a to 13.2.5u and 13.2.6a to 13.2.6k, the NT, WA and SA variations of those clauses, clauses 10.8.1 and 10.8.3; NCC 2025 Volume Two H6D2, S42C2 and S42C4; NCC 2022 Housing Provisions clauses 13.2.3, 13.2.5 and 13.2.6. Figures verified against the ABCB's published text on 4 September 2026. Diagram by AEC Assistant. This article is general guidance; the building surveyor or certifier for your project determines compliance.
