EN 12086 Thermal Insulation Products for Building Applications - Determination of Water Vapor Transmission Properties

A European standard "EN 12086 Thermal insulation products for building applications - Determination of water vapour transmission properties" describes equipment and procedures for determining the water vapour transmission rate, water vapour permeability and water vapour permeability of test specimens at steady state under different sets of specified test conditions. These procedures are also applicable to thermal insulation products.

This standard is intended for use with products that may include homogeneous materials and integrated coatings or surfaces made of different materials.

A material is considered to be homogeneous in terms of mass distribution if its density is approximately the same everywhere, that is, if the measured density values ​​are close to its average density.

This test method is not normally used to determine the water vapour transmission properties of single, discrete vapour barriers (with high diffusion resistance) because of the length of the test. For vapour retarder or barrier products with a water vapour diffusion equivalent air layer thickness of at least 1000 m, other test methods (e.g. IR detection) may be used to measure the single vapour retarder or barrier, provided that the results obtained are in the same range as the values ​​measured in accordance with this standard.

Water vapor transmission rate and permeability values ​​are specific to the test sample (i.e. product) tested. For homogeneous products, water vapor permeability is a property of the material.

For the purposes of this standard, the following terms and definitions apply:

• The water vapor transmission rate expresses the amount of water vapor transmitted through a unit area per unit time under specified temperature, humidity and thickness conditions.
• Water vapor permeability refers to the ratio of the water vapor transmission rate of the test sample and the water vapor pressure difference between the two sample surfaces during the test.
• Water vapor resistance is the reciprocal of water vapor permeability.
• Water vapor permeability is the product of the permeability and the thickness of the test specimen. The water vapor permeability of a homogeneous product is a property of the material. It is the amount of water vapor passing through a unit area of ​​the product per unit time per unit of vapor pressure difference between the surfaces of the product for a unit thickness.
• The water vapor diffusion resistance factor expresses the ratio of the water vapor permeability of air and the water vapor permeability of the corresponding material or homogeneous product. It shows the relative magnitude of the water vapor resistance of the product and the water vapor resistance of a fixed air layer of equal thickness at the same temperature.
• The water vapour diffusion equivalent air layer thickness refers to the thickness of a quiescent air layer having the same water vapour resistance as the test sample. Conversion tables and units for these definitions are included in the standard appendix (Annex A).

In principle, the test sample is sealed in the open side of a test vessel containing a desiccant or aqueous saturated salt solution. The assembly is then placed in a test atmosphere of controlled temperature and humidity. Water vapor flows through the test sample due to the difference in partial water vapor pressures in the test assembly and in the test atmosphere. When steady state is reached, periodic weighings of the assembly are made to determine the water vapor transmission rate.

The main equipment used in these tests includes:

• Test vessels: Test vessels, preferably circular in shape, resistant to any desiccant or salt solution (corrosion) they may contain and impermeable to water or water vapour. These vessels are usually made of glass or metal. The size of the vessels depends on the size of the test specimen to be tested. The difference in size between the upper exposed area and the lower exposed area of ​​the test specimen should be less than 3 per cent. Some types of test vessels are not suitable for use with certain materials. This should be specified in the relevant product standard or another European standard.
• Measuring instruments: Measuring instruments capable of determining linear dimensions in accordance with the EN 12085 standard.
• Template: Template corresponding to the shape and size of the test vessel to replicate the open area of ​​the specimen (with tapered edges to facilitate removal after use). The template should have an area that is at least 90 percent of the surface of the test specimen to limit edge effect due to nonlinear vapor flow.
• Analytical balance: capable of weighing the test fixture to an accuracy of plus/minus 1 mg or better. If larger test fixtures are used, weighing accuracy can be determined by the total weight and the required accuracy of the test results.
• Chamber: Chamber that can be maintained within plus/minus 3 percent of the required relative humidity and plus/minus 1 degree of the required temperature. Air circulation with an air velocity of between 0,02 m/s and 0,3 m/s may be required to maintain the required conditions throughout the chamber. If a non-injection type humidity chamber is used, saturated salt solutions may be used.
• Sealant: Unaffected by test conditions. Examples of suitable sealants are: a blend of 90 percent microcrystalline wax and 10 percent plasticizer (e.g., low molecular weight polyisobutylene) or 40 percent microcrystalline wax with 60 percent refined crystalline paraffin.

Test samples should be representative of the product and include natural surface shells or coatings of different materials. If the purpose is to measure the permeability of the core material, all shells and coatings should be removed and the test samples should be at least 20 mm thick. For coated products with a water vapour diffusion resistance index of at least 3, the permeability for the core material can be determined from measurements made on the coating itself after separation from the product. Test samples should be cut to fit the dimensions of the selected test fixture.

The thickness of the test specimen should be the same as the thickness of the product. If this exceeds 100 mm, the specimen thickness can be reduced by cutting.

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