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13 – Introduction to building thermography
Example for lightweight built-up cladding with defective
insulation
Good area
Failing area
Outside temperature in ℃
0
0
Inside surface temperature in ℃
19.1
15.0
Outside surface temperature in ℃
0.3
1.5
Surface factor from IP17/01
0.95
0.75
Critical external surface temperature factor, after IP17/01
0.92
Insulation thickness to give this level of performance, mm
80
5.1
Local U value W/m2K
0.35
1.92
UKTA TN1 surface factor
0.78
UKTA TN1 surface factor outside
0.93
Notes to the table
1 Values of surface resistances taken from ADL2 2001, are:
■
■
2
3
4
5
13
Inside surface 0.13 m2K/W
Outside surface 0.04 m2K/W
These originate from BS EN ISO 6946 (BN EN ISO 6946:1997 Building components
and building elements - Thermal resistance and thermal transmittance - Calculation
method).
Thermal insulation used here is assumed to have a conductivity of 0.03 W/m K.
The difference in temperature between an anomaly and the good areas is 1.2 degrees on the outside and 4.1 degrees on the inside.
The UKTA TN1 surface temperature factor for internal surveys is:
Fsi = (Tsia – Tso)/(Tsi – Tso)
where:
Tsia = internal surface temperature at anomaly
Tso = external surface temperature (good area)
Tsi = internal surface temperature (good area)
The UKTA TN1 surface temperature factor for external surveys is:
Fso = (Tsoa – Tsi)/(Tso – Tsi)
where Tsoa = external surface temperature at anomaly
13.3.8.4.3
Selecting maximum acceptable defect area
The allowable area of defect is a quality control issue. It can be argued that there
should be no area on which condensation, mould growth or defective insulation will
occur and any such anomalies should be included in the report. However, a commonly
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Publ. No. 1558324 Rev. a267 – ENGLISH (EN) – March 12, 2008