Target U-value
Wall insulation thickness calculator
This sizing page estimates how much insulation is needed to reach the target U-value for a wall insulation thickness calculator.
Used for quick thermal checks of walls, roofs, and floors.
Working calculator
Enter the core dimensions and check the result directly on this page.
How much insulation is needed to reach 0.25 W/m²K?
The sizing example starts from the base wall resistance, subtracts it from the target total resistance, and converts the remaining resistance into thickness.
The table below compares the insulating thickness needed for the most common materials used on this site.
U-value
What this example represents
This variant describes an assembly related to a wall. The page focuses on material, thickness, and the resulting U-value. Read the value as a conceptual comparison: it shows the effect of thickness and lambda, but it does not include every junction detail, fixing, or moisture condition.
The insulation material or assumption is an insulation layer. If there is no additional insulation, the result mainly shows the limits of the structural layer itself.
Masonry assemblies need attention at ring beams, lintels, balconies, and foundation junctions. Before using the result for construction decisions, check current product data, local requirements, layer continuity, and possible thermal bridges.
Compare this page with nearby variants rather than reading it in isolation. The most useful set is the no-additional-layer case, a minimum option, and an option with margin for installation error and material tolerance.
If the example covers services, concrete, or heating, use it as a starting point for range checking. Exact sizing still depends on standards, loads, pressures, protective devices, or local execution conditions.
Wall insulation thickness calculator
Wall insulation thickness calculator
Base wall build-up used for the estimate.
Assembly thickness
Assembly thickness
Remaining resistance is translated into insulation thickness.
U-value
U-value
Target U-value 0.25 W/m²K based on a wall insulation thickness calculator reference build-up.
CategoryLambdaLayerMaterialThickness
How it works
Target note
This is a quick reference page for planning. Use the full calculator to verify junctions and detailed layer ordering.
Thickness comparison
Mineral wool and EPS are shown because they are common search targets and give a fast comparison baseline.
Target U-value calculation
The target resistance is 1 / U. Once the base wall resistance is known, the remaining resistance can be turned into thickness for a chosen insulation material.
For this reference page, mineral wool and EPS are compared side by side so the page stays useful without being empty.
Add layerRestore default setupRemove
Assembly nameThickness unitInternal Rsi (m2K/W)External Rse (m2K/W)
Calculation assumptions
The calculators use visible formulas and explicit unit conversions. Treat the result as a preliminary check, not a complete building design.
- SI and US units are converted separately; R, RSI, U-value, and U-factor are not mixed without the unit factor.
- Enter positive values and compare the result with the selected product datasheet.
- Local codes, thermal bridges, fasteners, and installation quality can change the requirement.
- Last formula review: 2026-04-27.
See how formulas, unit conversions, rounding, and limitations are handled. Methodology details.
Frequently Asked Questions
Lambda is the thermal conductivity of a material, usually shown in W/mK. Lower lambda means heat moves through that material more slowly, but the final assembly still depends on thickness, surface resistances, and every other layer.
U-value describes heat loss through the whole building element, not just one material. A low U-value usually means a better insulated wall, roof, or floor, provided the real build-up matches the layers entered in the calculator.
Yes. Use the comparison section to keep thickness constant, then compare materials by lambda and calculated thermal resistance. This is useful when two products look similar on paper but behave differently at the same installed depth.
Yes. You can print the result or export it to CSV, Excel, or PDF for reports and documentation.
Yes. It is designed for layered assemblies such as external walls, flat roofs, pitched roofs, floors, and slabs. For unusual assemblies, add every relevant layer and treat the result as a planning check before formal verification.
Yes. It is intended for fast concept-stage calculations, insulation comparison, and envelope optimisation before detailed design. It is best used to narrow choices, not to replace a code check or project-specific thermal bridge assessment.
Yes. You can switch between millimeters, centimeters, and inches, and the calculator keeps the values consistent. For fewer mistakes, choose one unit system at the start of a project and review converted thicknesses before export.
Use Wall insulation thickness calculator as a first-pass reference. Before specifying anything, compare the result with the reveals and corners, actual project dimensions, product data sheet, and local requirements.