The introduction outlines when values in Table 2.35 should be used for U-value and solar transmittance derivation. The survey process provides information on window area, glazing type, age, frame type and orientation.
| Glazing | Low E coating | Frame | Metal thermal break assumed | U-value (W/m2K) (Table 6a) | Solar transmittance (Table 6b) | Basis for U and g values |
|---|---|---|---|---|---|---|
| Single | N/A | Wood/PVC | N/A | 4.8 | .85 | |
| Single | N/A | Metal | 4mm | 5.7 | .85 | |
| Single with secondary glazing | N/A | Wood/PVC | N/A | 2.4 | .76 | |
| Single with secondary glazing | N/A | Metal | 4mm | 2.4 | .76 | |
| Double – pre 2004 | No | Wood/PVC | N/A | 3.1 | .76 | Air filled, 6mm gap |
| Double – pre 2004 | No | Metal | 4mm | 3.7 | .76 | Air filled, 6mm gap |
| Double – 2004 to 2009 | Yes | Wood/PVC | N/A | 2.2 | .72 | Air filled, low E hard coat εn = .15, 12mm gap |
| Double – 2004 to 2009 | Yes | Metal | 4mm | 2.7 | .72 | Air filled, low E hard coat εn = .15, 12mm gap |
| Double – 2010 onwards | Yes | Wood/PVC | N/A | 2.0 | .72 | Argon filled, low E hard coat εn = .15, 12mm gap |
| Double – 2010 onwards | Yes | Metal | 4mm | 2.5 | .72 | Argon filled, low E hard coat εn = .15, 12mm gap |
| Triple Pre - 2010 | Yes | Wood/PVC | N/A | 1.7 | 0.64 | Air filled, low E hard coat εn = .15, 12mm gap |
| Triple Pre - 2010 | Yes | Metal | 4mm | 2.1 | 0.64 | Air filled, low E hard coat εn = .15, 12mm gap |
| Triple 2010 Onwards | Yes | Wood/PVC | N/A | 1.5 | 0.64 | Argon filled, low E hard coat εn = .15, 12mm gap |
| Triple 2010 Onwards | Yes | Metal | 4mm | 1.9 | 0.64 | Argon filled, low E hard coat εn = .15, 12mm gap |
When using Table 2.35 base the row selected on the age of the glazing and the frame type (wood/PVC/metal) and select the resulting U and g values.
Any other U-value and solar transmittance from Table 2.28/Table 2.31 may be chosen subject to the guidance under Table 2.28/Table 2.31 provided supporting evidence is available.
Adjustments for roof windows apply as per new dwellings.
If the assessor chooses to use the default window U-value and solar transmittance from Table 2.35, the following defaults are assumed:
Installed before 2004:
Glass is uncoated, with 6mm air filled gap. Metal framed window thermal break is 4 mm for metal framed windows.
Installed 2004-2009:
Glass is hard coated with εn = 0.15. 12 mm air filled gap. Metal framed window thermal break is 4 mm.
Installed 2010 onwards:
Glass is hard coated with εn = 0.15. 12 mm argon filled gap. Metal framed window thermal break is 4 mm.
The following examples show use of Table 2.35 to determine U-value and solar transmittance defaults:
Where an assessor encounters retrofitted / upgraded glass in an existing window frame, they will most likely need to resort to the default window U-values in DEAP. Non-default values are used where there is sufficiently evidenced information to carry out a calculation to EN10077-1. It is unlikely that EN10077-2 (detailed calculation) or EN12567 (measurement) would be feasible in this case.