Overview
EN ISO 12567-2:2005 (ISO 12567-2:2005) defines a laboratory procedure to determine the thermal transmittance (U-value) of roof windows and other projecting windows using the hot box method. Published by CEN/ISO, the standard provides a repeatable test arrangement and measurement rules to produce standardized U-values for product comparison and declaration. It expressly excludes energy transfer due to solar radiation, air leakage through the specimen and edge effects occurring outside the specimen perimeter.
Key topics and technical requirements
- Test method: Hot box measurement following the general principles in ISO 8990 and the specimen-specific rules in ISO 12567-1, adapted for projecting/roof windows.
- Specimen mounting: Roof windows are mounted in a surround panel flush with the cold face (insert- or kerb/curb-mounted) and include normal flashings/kerb details to reflect real installations.
- Calibration: Calibration panels (CTS) must be installed flush with the cold face and calibration measurements performed at the same orientation as the specimen.
- Orientation: Vertical mounting of roof-window specimens is acceptable for product declaration and comparison, but orientation affects measured U-values (heat flow direction matters).
- Baffle and airflow: The cold-side baffle-to-glazing distance must be ≥ 80 mm (greater for air speeds > 2 m/s). Air velocity on the cold side during specimen tests must match calibration within ±10%.
- Edge-zone considerations: Linear thermal transmittance of the edge zone is addressed (annex material), but effects occurring outside the specimen perimeter are excluded from the scope.
- Measurement basis: Tests are steady-state and follow the environmental temperature and instrumentation arrangements specified in the standard and its annexes.
Applications
- Generating standardized U-values for roof windows, skylights and projecting glazed units.
- Comparative product testing and product performance declaration for manufacturers.
- Laboratory verification for certification and compliance with building regulations and energy-label schemes.
- Supplying validated input data for building energy simulations (with caution-orientation corrections may be needed).
Who should use this standard
- Test laboratories and calibration facilities performing thermal transmittance measurements.
- Window, skylight and façade manufacturers preparing product declarations.
- Certification bodies, specifiers, architects and façade engineers assessing thermal performance.
- Energy modelers needing standardized material U-values for building simulation (use alongside orientation-correction methods).
Related standards
Keywords: EN ISO 12567-2:2005, ISO 12567-2, thermal transmittance, U-value, hot box method, roof windows, projecting windows, skylights, calibration panel, baffle distance.
