NCC 2016 Volume Two
ACT 7.1.4 External Glazing - Application of Part 3.12.2

ACT 7.1.4 External Glazing - Application of Part 3.12.2


Subject to (b), in applying Part 3.12.2 to an addition or extension all glazing on the respective storey, including the addition or extension and any existing glazing in the unaltered part of the storey, must be assessed where Part 3.12.2 indicates the whole storey must be assessed. However, the Total System U-Value of an existing glazing unit in the unaltered part of the building can take account of any of the following:


Window treatments listed in Table ACT, to the extent provided in that table, where the glazing unit incorporates the respective treatment in compliance with the notes to that table.


Window shutters mentioned in Annex G of international standard ISO 10077-1, (Thermal performance of windows, doors and shutters — Calculation of thermal transmittance), where the glazing unit is readily closed in by the shutters, and the shutters can be readily opened so they do not shade the glazing of the unit, and the closed shutters comply with the respective construction, material and permeability provisions of that Annex G.



The Total System U-Value of the existing glazing unit, incorporating shutters, can be calculated by adding the inverse of the respective shutters’ value of additional thermal resistance, ΔR, from Table G.1 (Additional thermal resistance for windows with closed shutters), of the above-mentioned Annex G.


ACT 7.1.4(a) does not apply to windows otherwise dealt with under (c) or (d).


If an addition or alteration fails to incorporate a wall that can contain translucent glazing with an area of at least 1 m2 or 1% of the addition’s or alteration’s floor area, whichever is the greater, not overshadowed by a building in winter, and orientated within the north sector shown in Figure, then all glazing (existing or otherwise) in the storey need not comply with the requirements of that relate to aggregate conductance of the glazing if—


the addition or alteration has a total floor area not exceeding 50 m2; and


compliance with the requirements of that relate to aggregate conductance of the glazing would not result in a building (or part thereof), as extended or altered, having its energy efficiency reduced below—


the relevant statutory minimum, which is the minimum energy efficiency requirement, if any, that all or part of the building, respectively, was required to achieve when constructed or altered; or


for a building that has not been altered or extended, the current energy efficiency of the building, which is the lesser of its energy efficiency determined using the factors Part 3.12 covers, or the energy efficiency it would be required to achieve under Part 3.12 if it was to be built; or


for the following parts of a building—an unaltered, unextended, altered, or extended part—the energy efficiency for the part as per (ii) as if (ii) applied to the part—


the aggregate conductance of the glazing is in accordance with BCA requirements that applied in the ACT immediately before or anytime after the adoption of BCA 2010 in the ACT; and


bulk thermal insulation has been added to the roof of the unaltered part of the building, in accordance with the requirements of that apply to roofs with an upper surface solar absorptance value of not more than 0.4.


The Building (General) Regulation 2008, section 29 (Unaltered parts need not comply with building code—alternative energy efficiency requirements for external glazing Act, s 29 (2) (b)) prescribes when windows with solar control film or when "isolated glazing" need not comply with the BCA, Part 3.12.2, in relation to a substantial alteration mentioned in the Building Act 2004, section 29 (Approval requirements). Those alternative energy efficiency provisions may apply to existing windows that ACT 7 applies to whether or not the window is in respect of a "substantial alteration" as defined in the Building (General) Regulation 2008, section 23 (Substantial alteration—Act 29 (2) (a)). However, the storey's area mentioned in must exclude the enclosed area, ΔA, that the isolated glazing unit is located in. Isolated units must be in an area enclosed by walls and doors (a "zone"), and all glazing units in the zone must be treated as isolated units. ΔA is the zone's area, and must be counted only once for a particular zone, even if the zone has more than one isolated unit. If the ABCB's glazing calculator is used to demonstrate compliance, isolated unit details need not be entered (they may be disregarded), and if so, the entry for the storey's area must be reduced by the sum of each ΔA value for each zone. The ΔA reduction does not apply to glazing units disregarded because of the solar control film, because they lack zone requirements.

Figure ACT 7.1.4

Diagram a. Addition incorporating a wall within the north sector


Note: Plan showing a method of compliance with certain requirements of ACT 7.1.4(a) and (b), in assessing window energy efficiency as part of a deemed-to-satisfy alternative to using house energy efficiency rating software.

Figure ACT 7.1.4

Diagram b. Addition incorporating a wall within the north sector


Note: Plan showing a method of compliance with certain requirements of ACT 7.1.4(c), in assessing window energy efficiency as part of a deemed-to-satisfy alternative to using house energy efficiency rating software, where the ABCB’s 2009 glazing calculator may be used rather than the current calculator, as a concession.

Table ACT Glazing unit U-Values

Glazing unit (not taking account of any window treatments) Improved U-Values with window treatments
U-Value R-value Holland blinds only Closed weave curtains only Heavy drapes only Closed weave curtains & pelmet Heavydrapes & pelmet
7.8 0.13 6.32 6.32 5.46 4.20 2.18
7.6 0.13 6.19 6.19 5.36 4.14 2.17
7.4 0.14 6.06 6.06 5.26 4.08 2.15
7.2 0.14 5.92 5.9 5.16 4.02 2.13
7.0 0.14 5.79 5.79 5.05 3.95 2.11
6.8 0.15 5.65 5.65 4.95 3.89 2.10
6.6 0.15 5.51 5.51 4.84 3.82 2.08
6.4 0.16 5.37 5.37 4.73 3.76 2.06
6.2 0.16 5.23 5.23 4.62 3.69 2.04
6.0 0.17 5.08 5.08 4.51 3.61 2.01
5.8 0.17 4.94 4.94 4.40 3.54 1.99
5.6 0.18 4.79 4.79 4.28 3.47 1.97
5.4 0.19 4.65 4.65 4.16 3.39 1.94
5.2 0.19 4.50 4.50 4.04 3.31 1.91
5.0 0.20 4.35 4.35 3.92 3.23 1.89
4.8 0.21 4.20 4.20 3.80 3.14 1.86
4.6 0.22 4.04 4.04 3.67 3.05 1.83
4.4 0.23 3.89 3.89 3.54 2.96 1.79
4.4 0.23 3.89 3.89 3.54 2.96 1.79
4.0 0.25 3.57 3.57 3.28 2.78 1.72
3.8 0.26 3.41 3.41 3.14 2.68 1.69
3.6 0.28 3.25 3.25 3.01 2.58 1.65
3.4 0.29 3.09 3.09 2.86 2.47 1.60
3.2 0.31 2.92 2.92 2.72 2.37 1.56
3.0 0.33 2.75 2.75 2.58 2.26 1.51
2.8 0.36 2.58 2.58 2.43 2.14 1.46
2.6 0.38 2.41 2.41 2.27 2.02 1.40
2.4 0.42 2.24 2.24 2.12 1.90 1.34
2.2 0.45 2.06 2.06 1.96 1.77 1.27
2.0 0.50 1.89 1.89 1.80 1.64 1.20
1.8 0.56 1.71 1.71 1.64 1.50 1.13
1.6 0.63 1.53 1.53 1.47 1.36 1.05
1.4 0.71 1.34 1.34 1.30 1.21 0.96
1.2 0.83 1.16 1.16 1.13 1.06 0.86
1.0 1.00 0.97 0.97 0.95 0.90 0.75
0.8 1.25 0.78 0.78 0.77 0.74 0.63
0.6 1.67 0.59 0.59 0.58 0.56 0.50


  1. Values in the table may be interpolated to more accurately reflect U-Values.
  2. Closed weave curtains have threads or yarns that generally abut, producing a fabric with negligible interstices. Thus, light, air and water pass through a closed weaved cotton fabric, but with significant filtering, unless the fabric is treated to block their passage; and they prevent visual detail being seen by eye through their fabric if woven from opaque thread or yarn. Closed weave curtains do not include open weave curtains, as open weave curtain fabric is woven so that warp threads rarely abut each other, leaving interstices in the fabric, which includes lace, sheer or net fabrics. Open weave curtains provide negligible change to the Total System U-Value.
  3. Heavy drapes permit no or negligible visible or UV light to pass through their fabric, which may include a composite of layered materials. They also do not readily allow air to pass through. They include closed weave heavy fabrics, such as velvet or velour or heavy cotton or comparable synthetics, with a rubber, acrylic, or similar, solar blocking backing layer bonded to the fabric. The presence of a light source, including the sun, cannot be detected by an unaided eye through the fabric. Another requirement of heavy drapes is to have sufficient inertia to maintain a barrier to air movement by remaining relatively stationary in a draft.
  4. Drapes or curtains must fully cover the window and form part of an enclosure of the layer of air between the drape or curtain and window to minimise air movement caused by convection air currents and air movement cause by HVAC systems, fans, or use of the room. That is achieved where curtains or drapes—
    1. are fully within and abut the window recess (reveals) and abut the reveals, head and sill; or
    2. overlap the side edges of the window by at least 150 mm, or abut a return wall if the window is in a re-entrant corner, and abut the floor; and
    3. close together (where openable) with no, or with negligible gaps.

    For the purposes of this note, a drape or curtain is taken to abut a surface where the drape or curtain is not more than 10 mm from that surface.

  5. Pelmets must be box pelmets and must work in combination with the curtain or drape to enclose the top of a curtain or drape to prevent air plunging by convection from beside or above the pelmet to the window, and must extend to the width of the window plus any required curtain overlap of the window edge. It must overlap the top of the curtain by 50 mm or more.