Thermal Insulation Savings
Calculate U-value and required insulation thickness
How the calculation works
Choose the wall and plaster materials, enter their thicknesses and the target U-value. From the thermal resistance of each layer the calculator works out the current U, the insulation thickness needed and an estimated energy saving.
Formula and assumptions
Layer R = thickness (m) ÷ λ. Total R = R(si) 0.13 + layer R values + R(se) 0.04 (m²K/W). U = 1 ÷ R. Required insulation thickness = (1 ÷ target U − existing wall R) × insulation λ, rounded up to a standard thickness. λ values are indicative – use manufacturer data.
Worked example
Hollow brick 25 cm (λ 0.30): R = 0.25 ÷ 0.30 = 0.833; with surface resistances R = 1.003, U ≈ 1.00 W/m²K. Target U = 0.30 → R = 3.33; 2.33 m²K/W of insulation needed. EPS (λ 0.039): 2.33 × 0.039 = 9.1 cm → standard 10 cm.
What affects real consumption
- The actual λ value and moisture content of the material.
- Thermal bridges (fixings, anchors, ring beams).
- Quality of installation and airtightness.
Frequently asked questions
What is a U-value?
The thermal transmittance in W/m²K; the lower it is, the better the element insulates.
Is the energy saving exact?
No – it is an estimate from the temperature difference, heating hours and system efficiency entered; the real saving depends on habits and the building.