Building envelope quality is crucial to the energy performance, longevity and comfort of buildings. Envelopes must therefore meet many scientific and technical requirements. In Grenoble, the CSTB has a facility where 26 different tests are conducted to characterize the performance of envelope materials and components, in accordance with quality assurance standards or COFRAC No. 1-1542 accreditation (scope available on www.cofrac.fr). The CSTB guides industrial companies and consulting firms in designing innovative products and in the assessment and certification process.
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Analyzing optical and radiative properties
To determine the impacts of materials and components on envelope energy performance, the CSTB laboratory performs two types of analyses:
- On opaque and translucent materials and components (coating, closures, glazing, light transmitting sheets, etc.), for which the laboratory can characterize behavior when interacting with sources of natural and artificial radiation. This includes measuring optical properties (transmission, reflections and solar and light absorption) and investigating infrared emissivity.
- On facade materials and components, for which the laboratory analyzes solar heat gain (determination of g-value).
- concerning complex translucent facade components, the CSTB has developed a device, the G-meter, for taking measurements to establish the thermal balance of samples placed in climate-controlled conditions exposed (or not) to a solar flux. The g-value is deduced by taking the energy balances of the measurement chamber for the submitted sample, and comparing them with a reference sample.
To predict changes in building appearance over time, the colorimetric parameters of building materials and components are analyzed to characterize their stability or risk of color deviations or yellowing due to ageing and wear. This type of measurement can also be performed on all kinds of fabrics (sunshades, tent canvas, etc.).
Determining moisture transmission and air tightness
Long-term preservation of the quality and energy performance of buildings requires controlling excessive moisture and ensuring air tightness. To make this possible, the CSTB laboratory analyzes:
- Moisture transfer in the interior walls of buildings. This involves preventing the risk of condensation and degradation (mold, fungi, corrosion, hydrolysis, etc.).
- Air infiltration of materials, components and buildings (air permeability tester for materials and components; blower door test for buildings).
Based on the physical characteristics measured in the laboratory, the CSTB can also use simulation (WUFI®) to determine risks of disease related to envelope moisture.
Assessing thermal properties
It is invaluable to know the intrinsic thermal properties of envelope materials and components, as well as partition walls, to optimize building insulation. Various tests can help determine these properties: thermal conductivity; specific heat capacity and dynamic thermal behavior.
In particular, to assess the quality of cellular insulation, the laboratory tests rigid expanded foams, which can contain gases other than air. Gas diffusion is assessed using gas chromatography and by analyzing the open-cell percentage using pycnometric density measurements.
Testing mechanical and physiochemical properties
To ensure building quality and safety, the CSTB offers testing of the following:
- Mechanical strength, to determine resilience to impacts (tensile strength, compression, bending and impact resistance);
- Chemical stability during temperature changes if the product is made of rubber or elastomer materials (characterization of the infrared spectrum, thermogravimetric analysis).
Analyzing durability
This consists of assessing the performance of materials used outdoors. Sunshine, freeze-thaw action, heat, cold and moisture can be simulated with climatic enclosures and weatherometers for natural or accelerated in-situ ageing of materials.
The performance of materials is analyzed before and after ageing using optical, mechanical and physicochemical techniques.
