The Thermal Measurement Center of the Institute of Numerical Modeling (SMI) of the University of Latvia is expanding its accreditation scope and is now competent to perform testing for water vapor permeability!
Until now, the center was accredited for testing the thermal conductivity of materials λ [W/(m×K)] in accordance with the requirements of the international standard LVS EN 12667, but in October 2025, a new area was successfully added to the accreditation – determining the hygrothermal properties and water vapor permeability of building materials in accordance with the requirements of the LVS EN 12572 standard. Now we can also offer measurements of the water vapor diffusion resistance of materials μ [-] and the diffusion-equivalent air layer thickness Sd [m] for samples up to 5 cm thick.
Water vapor permeability parameters are important for ensuring the optimal moisture regime and sustainability of building materials and structures. They help predict the moisture content and its changes in materials and building elements, preventing the formation of condensation, which can cause mold growth, material degradation and loss of energy efficiency. In 2025, the Center for Thermal Physical Measurements The installation and calibration of a thermal camera (HotBox) (pictured) has also been completed, which allows standardized testing of the thermal transmittance (U-value) of finished building structures (windows, doors, panels, blocks, and similar elements of external envelope structures). It is planned to expand the scope of accreditation for U-value measurements in the coming months.
Some of the areas where the new vapor permeability testing capabilities will be particularly useful:
- Timber frame construction and roof systems
Problem: High risk of moisture accumulation in frame structures and low-slope roof insulation.
Importance: Sd measurements allow for the correct selection and combination of vapor barriers (inside) and diffusion membranes (outside). Incorrect selection causes moisture to be trapped in the insulation, which critically deteriorates thermal insulation capabilities (symbol L – thermal conductivity – increases, energy efficiency decreases) and promotes wood rotting. - Renovation and insulation of historic buildings
Problem: Insulation of old, solid walls (brick/concrete) with new, insufficiently vapor-permeable systems.
Importance: Accurate μ and Sd measurements ensure that the selected insulation is sufficiently permeable in relation to the old wall material. This avoids moisture trapping between layers and structural damage. The principle must be followed: “tighter inside, more permeable outside.” - Design of special premises (swimming pools, production workshops)
Importance: Testing allows the design of particularly high-performance vapor barrier layers, ensuring that the impact of constant moisture is not transferred to the load-bearing structures. This helps maintain the technical condition of the building and reduce energy consumption for drying the premises.
Problem: Constantly high indoor humidity creates a huge load on external structures.
The extension of this accreditation significantly strengthens the position of the LU SMI Thermal Physical Measurement Center as the leading hygrothermal properties testing partner in the Baltics. By offering accurate MU and Sd measurements, the center provides construction professionals and material manufacturers with critical information for designing long-lasting, energy-efficient and safe building structures. We encourage industry representatives to use this newly developed expertise to prevent moisture-related risks at an early stage, thus ensuring the highest construction quality and sustainability.
