EN ISO 10077 Thermal Performance of Windows, Doors and Shutters - Calculation of Thermal Transmittance

As energy efficiency becomes an increasingly global priority, the construction industry faces increasing pressure to design buildings that reduce energy consumption. A critical component of this effort is the thermal performance of windows and doors, which significantly impact a building's heat loss or gain. The ISO 10077 standard plays a key role in establishing criteria and methodologies for assessing this thermal performance.

The “ EN ISO 10077 Thermal performance of windows , doors and shutters - Calculation of heat transmittance” standard, which is based on a European standard and was later published by the International Organization for Standardization (ISO) , consists of the following sub-sections published under the same title:

• The standard "EN ISO 10077-1 Part 1: General" describes methods for calculating the thermal transmittance of windows and pedestrian doors with or without shutters, consisting of glazed or opaque panels placed in frames. This standard allows:
  • Different types of glazing (glass or plastic, single or multiple glazing, with or without low-emissivity coating and with voids filled with air or other gases)
  • Opaque panels inside windows or doors
  • Various frame types (wood, plastic, metallic with and without heat barriers, metallic with precision metallic joints, or any combination of materials)
  • Additional thermal resistance provided by different types of closed shutters or external shutters, where appropriate, depending on their air permeability.

The thermal transmittance of roof windows and other projecting windows can be calculated in accordance with this standard, provided that the thermal transmittance of the frame sections is determined by measurement or numerical calculation. Default values ​​for glazing, frames, and shutters are given in the appendices. Thermal bridging effects at the slat or joint between the window or door frame and the rest of the building envelope are excluded from the calculation.

The calculation does not include:

• Effects of solar radiation
• Heat transfer due to air leakage
• Condensation calculation
• Ventilation of air gaps in double and combined windows
• The surrounding sections of a bay window.

This standard does not apply to: curtain walls and other structural glazing, and industrial, commercial, and garage doors.

The table provided within the standard shows the relative position of this standard within the set of EPB standards in relation to the modular structure specified in ISO 52000-1. The EPB standard refers to a standard that complies with the requirements specified in ISO 52000-1, CEN/TS 16628, and CEN/TS 16629.

• The standard "EN ISO 10077-2 Part 2: Numerical method for frames" describes a method for calculating the linear thermal transmittance of frame profiles and their connections to glass or opaque panels, and provides reference input data. This method can also be used to evaluate the thermal resistance of shutter profiles and the thermal properties of shutter boxes and similar components (e.g., shutters). This standard also provides criteria for validating the numerical methods used for calculation.

This standard does not include the effects of solar radiation, heat transfer caused by air leakage, or three-dimensional heat transfer such as sensitive metallic connections. Thermal bridging effects between the frame and the building structure are not included.

The table provided within the standard shows the relative position of this standard within the set of EPB standards in the context of the modular structure specified in ISO 52000-1.

In short, EN ISO 10077 is an international standard that specifies methods for calculating the thermal transmittance (U-value) of windows, doors, and shutters. The U-value is important in determining how well a product insulates against heat transfer. Thermal transmittance (U-value) represents the rate of heat transfer within a structure. The lower the U-value, the better the insulation. EN ISO 10077 defines how to calculate the total U-value, taking into account the following factors:

• Frame and glass areas
• Linear thermal bridges at the glass edge
• Spacers and other components

Particular attention is paid to frame materials and configurations. While EN ISO 10077 includes default value tables, it also allows for specific measurements using advanced simulation tools, as described in EN ISO 10077-2. For applications requiring high accuracy, EN ISO 10077-2 outlines how to use two-dimensional finite element modeling to simulate heat flow. This method provides precise U-values ​​for specific products, taking into account geometric complexity and material inhomogeneity.

The primary objective of the EN ISO 10077 standard is to ensure consistent and reliable assessment of window and door thermal performance among manufacturers, designers, and regulators. This helps:

• To compare products according to their insulation performance.
• Supporting building energy performance simulations.
• To comply with national and international energy regulations.

This standard applies to all glazing systems, including:

• Frame and sash materials (e.g. wood, aluminum, PVC)
• Single, double and triple glazing
• Shutters and opaque panels

Consequently, the EN ISO 10077 standard is a fundamental element in assessing the energy efficiency of windows and doors. By providing clear methodologies for calculating thermal transmittance, it enables manufacturers, architects, and engineers to design products and buildings that meet modern energy performance demands. As global efforts towards sustainability intensify, standards like EN ISO 10077 will continue to be vital tools in shaping the future of green construction.

Our organization, which has been supporting businesses across all sectors for years through a wide range of testing, measurement, analysis, and evaluation activities, has a strong team of employees who closely follow global developments in science and technology and are constantly improving themselves. In this context, we also provide testing services in accordance with the EN ISO 10077 standard: Thermal performance of windows, doors, and shutters - Calculation of thermal transmittance.