# Specification 37
Specification 37 relates to the calculation of the U-value and solar admittance of building elements, which are important factors in determining the overall energy efficiency of a building.
It specifies the methods that should be used to calculate the U-value and solar admittance of building elements. It provides tables of default values for different types of materials and constructions.
The calculations consider factors such as the thickness and thermal conductivity of the material, as well as any air gaps or reflective surfaces that may affect the overall performance.
#### 1. Scope
This specification describes the methods of calculating the *U-Value* and *solar admittance* of a *wall-glazing construction*.
#### 2. General
For determining the aspect of a *wall-glazing construction*—(a)
the northern aspect is at or within 45° of true north; and
(b) the southern aspect is at or within 45° of true south; and
(c) the eastern aspect is within 45° of true east; and
(d) the western aspect is within 45° of true west.
#### 3. U-Value — Method 1 (Single Aspect)
(a) For the purposes of this method, a *wall-glazing construction* only includes the walls and *glazing* facing a single aspect.
(b) The *Total system U-Value* of the wall component of a *wall-glazing construction* must be calculated as the inverse of the *Total R-Value*, including allowance for thermal bridging, in accordance with—
(i) AS/NZS 4859.2; or
(ii) Specification 38 for *spandrel panels*.
(c) The *Total system U-Value* of a *wall-glazing construction* must be calculated as the area-weighted average of the *Total system U-Value* of each of the components of the *wall-glazing construction*.
(d) The *Total system U-Value* must not exceed the applicable value in J1.5(a).
#### 4. U-Value — Method 2 (Multiple Aspects)
(a) For the purposes of this method, a *wall-glazing construction* only includes the walls and *glazing* facing multiple aspects.
(b) The *Total system U-Value* of the wall component of a *wall-glazing construction* must be calculated as the inverse of the *Total R-Value*, including allowance for thermal bridging, in accordance with—
(i) AS/NZS 4859.2; or
(ii) Specification 38 for *spandrel panels*.
(c) The *Total system U-Value* of a *wall-glazing construction* must be calculated as the area-weighted average of the *Total system U-Value* of each of the components of the *wall-glazing construction*.
(d) The *Total system U-Value* must not exceed the applicable value in J1.5(a).
#### 5. Solar admittance — Method 1 (Single Aspect)
(a) The *solar admittance* of a *wall-glazing construction* must be calculated in accordance with the following formula:
$$
\text{SA} = \frac{\text{AW1} \times \text{SW1} \times \text{SHGCW1}}{\text{AWall}} + \frac{\text{AW2} \times \text{SW2} \times \text{SHGCW2}}{\text{AWall}} + \dots
$$
where—\
SA = the *wall-glazing construction* *solar admittance*; and\
AW1, AW2, etc = the area of each *glazing* element; and\
SW1, SW2, etc = the shading multiplier for each *glazing* element in accordance with Clause 7; and\
SHGCW1, W2, etc = the *Total system SHGC* of each *glazing* element; and\
AWall = the total *wall-glazing construction* area.
(b) The *solar admittance* of the *wall-glazing construction* must not exceed the applicable value in J1.5(e).
#### 6. Solar admittance — Method 2 (Multiple Aspects)
The *solar admittance* of *wall-glazing construction* must achieve a representative *air-conditioning* energy value less than that achieved by the reference *solar admittance*, when using the following formula:
$$
\begin{aligned}
& \text{Er} = \text{A}*\text{N} \times \alpha*\text{N} \times \text{SA}*\text{N} + \text{A}*\text{E} \times \alpha\_\text{E} \times \text{SA}*\text{E} \\
& + \text{A}*\text{S} \times \alpha\_\text{SA} \times \text{S}*\text{S} + \text{A}*\text{W} \times \alpha\_\text{W} \times \text{SA}\_\text{W}
\end{aligned}
$$
where—\
ER = the representative *air-conditioning* energy value; and\
AN, E, S, W = the area of the *wall-glazing construction* facing each aspect; and\
αN, E, S, W = the *solar admittance* weighting coefficient of each aspect equal to—
(a) where the *glazing* area on an aspect is less than 20% of the *wall-glazing construction* area, 0; and
(b) the values in Table S37C6a and Table S37C6b; and
SAN, E, S, W = the *wall-glazing construction* *solar admittance* of each aspect—
(a) equal to the applicable value in J1.5(b) in the reference case; and
(b) calculated in accordance with Clause 5(a) in the proposed case.
**Table S37C6a Solar admittance weighting coefficient — Class 2 common area, Class 5, 6, 7, 8 or 9b building or Class 9a building other than a ward area**
| | *Climate zone* 1 | *Climate zone* 2 | *Climate zone* 3 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 4 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 5 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 6 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 7 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 8 |
| --------------- | ---------------- | ---------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Northern aspect | 1.47 | 1.95 | 1.95 | 2.05 | 2.28 | 2.12 | 2.40 | 1.88 |
| Southern aspect | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Eastern aspect | 1.39 | 1.58 | 1.63 | 1.72 | 1.72 | 1.62 | 1.84 | 1.92 |
| Western aspect | 1.41 | 1.68 | 1.65 | 1.69 | 1.75 | 1.67 | 1.92 | 1.25 |
**Table S37C6a Solar admittance weighting coefficient — Class 3 or 9c building or Class 9a ward area**
| | *Climate zone* 1 | *Climate zone* 2 | *Climate zone* 3 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 4 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 5 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 6 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 7 | [*Climate zone*](https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-three-amendment-1/schedule-3-defined-terms/schedule-3-definitions#id5915c518-564d-4782-a026-f94c3f1acd5e) 8 |
| --------------- | ---------------- | ---------------- | ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Northern aspect | 1.42 | 1.77 | 1.72 | 1.55 | 1.88 | 1.52 | 1.60 | 1.24 |
| Southern aspect | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 | 1.00 |
| Eastern aspect | 1.30 | 1.49 | 1.48 | 1.37 | 1.48 | 1.28 | 1.35 | 1.26 |
| Western aspect | 1.37 | 1.54 | 1.50 | 1.36 | 1.52 | 1.33 | 1.40 | 1.05 |
#### 7. Shading
For the purpose of calculating *solar admittance*, the shading multiplier is—(a)
for shading provided by an external permanent projection that extends horizontally on both sides of the *glazing* for the same projection distance P, as shown in Figure 7—
(i) the value in Table S37C7a for shading on the northern, eastern or western aspects; or
(ii) the value in Table S37C7b for shading on the southern aspect; or
(b) 0.35 for shading that is provided by an external shading device such as a shutter, blind, vertical or horizontal building screen with blades, battens or slats, which—
(i) is capable of restricting at least 80% of summer solar radiation; and
(ii) if adjustable, will operate automatically in response to the level of solar radiation.
**Table S37C7a Shading multipliers — Northern, eastern and western aspects**
| G/H | P/H = 0 | P/H = 0.1 | P/H = 0.2 | P/H = 0.3 | P/H = 0.4 | P/H = 0.5 | P/H = 0.6 | P/H = 0.7 | P/H = 0.8 | P/H = 0.9 | P/H = 1 |
| :-----: | :-----: | :-------: | :-------: | :-------: | :-------: | :-------: | :-------: | :-------: | :-------: | :-------: | :-----: |
| **0** | 1.00 | 0.90 | 0.80 | 0.72 | 0.64 | 0.57 | 0.51 | 0.46 | 0.41 | 0.38 | 0.35 |
| **0.1** | 1.00 | 0.95 | 0.89 | 0.81 | 0.74 | 0.66 | 0.59 | 0.52 | 0.47 | 0.42 | 0.40 |
| **0.2** | 1.00 | 0.98 | 0.94 | 0.89 | 0.82 | 0.75 | 0.68 | 0.62 | 0.56 | 0.51 | 0.47 |
| **0.3** | 1.00 | 1.00 | 0.97 | 0.94 | 0.89 | 0.84 | 0.78 | 0.72 | 0.66 | 0.61 | 0.57 |
| **0.4** | 1.00 | 1.00 | 0.99 | 0.97 | 0.94 | 0.90 | 0.86 | 0.82 | 0.77 | 0.73 | 0.68 |
| **0.5** | 1.00 | 1.00 | 1.00 | 0.99 | 0.97 | 0.95 | 0.92 | 0.90 | 0.86 | 0.83 | 0.79 |
**Table S37C7b Shading multipliers — Southern aspect**
G/H
P/H = 0
P/H = 0.1
P/H = 0.2
P/H = 0.3
P/H = 0.4
P/H = 0.5
P/H = 0.6
P/H = 0.7
P/H = 0.8
P/H = 0.9
P/H = 1
0
1.00
0.93
0.87
0.82
0.77
0.73
0.69
0.65
0.62
0.60
0.58
0.1
1.00
0.97
0.93
0.88
0.84
0.79
0.75
0.71
0.67
0.64
0.62
0.2
1.00
0.98
0.96
0.93
0.89
0.85
0.81
0.77
0.73
0.70
0.68
0.3
1.00
0.99
0.98
0.96
0.93
0.90
0.87
0.83
0.80
0.77
0.74
0.4
1.00
1.00
0.99
0.98
0.96
0.94
0.91
0.89
0.86
0.84
0.81
0.5
1.00
1.00
0.99
0.99
0.98
0.96
0.95
0.93
0.91
0.90
0.88
**Figure 7** Permanent external shading - Measurement of P, G and H
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