In the case of large and complex buildings, it may be impractical for the thermographic survey and airtightness testing to cover 100% of the building. Where a complete thermographic survey is deemed impractical by a Level 2 qualified thermographic surveyor, the guidance in airtightness standard TSL2 (or relevant local standard) should be followed on the extent of the survey and testing. This could include, for example, airports, large hospitals, high-rise buildings.