Frequently Asked Questions

Lambda describes the thermal conductivity of a material. A lower value means heat moves through the material more slowly, but lambda alone does not describe a full assembly. Thickness, layer position, and adjacent materials are also needed.

R-value shows the thermal resistance of one layer or a set of layers. U-value shows heat transfer through the complete assembly. A high R-value usually helps produce a low U-value, but the final result depends on the whole construction.

The calculators use common building units: millimetres, metres, W/mK, and m²K/W. The most common input mistakes are mixing millimetres with metres or using manufacturer values measured under different reference conditions.

Accuracy is suitable for estimates and option comparison, but it does not replace an energy assessment or professional design. Thermal bridges, moisture, fixings, gaps, and local regulations require separate review.

Manufacturer values can vary because of density, composition, test method, moisture, and declared use. If the database and a product sheet differ, use the current manufacturer documentation for final decisions.

Choosing insulation should combine thermal performance with installation, fire behaviour, acoustics, moisture, and durability. Walls, roofs, and floors can use similar formulas, but their construction details and local requirements differ.

If you find a material-data or translation issue, send the page URL, values, and a short explanation to contact@lambdacalculator.eu. These corrections help keep the database useful rather than just static reference text.

Surface resistances matter because they describe the conditions on each side of the assembly. The same layers can produce a different result when calculated as an external wall, roof, ground floor, or internal element.

The calculator can be used for walls, roofs, and floors, but each element has different details. A roof needs moisture and ventilation checks, a floor needs load and level checks, and a wall needs thermal bridge attention.

Local building rules matter because required U-values, calculation methods, and exceptions vary by country, region, and building type. The tool helps prepare data, but it does not interpret regulations for a project.

If a manufacturer lists several lambda values, use the one that matches the application, density, and declared conditions. Very favourable or unclear values should be confirmed in the technical data sheet before comparison.

Keep input data with the result. A layer list, thicknesses, lambda values, units, and check date make the calculation repeatable and explain why a later result may differ.

The calculator can support a discussion with a professional because it organizes thicknesses, lambda values, units, and result. It does not replace the responsibility of the person who signs the design or selects the construction solution.

If the result differs from a manufacturer tool or energy assessment, compare the assumptions step by step. Differences often come from surface resistances, rounding, thermal bridges, or boundary conditions.

Best practice is to keep a copy of the assumptions with the result. That makes it easy to return to the calculation after changes in material, price, standard, or local requirement.