Thermal Transmittance (U-Value)Shows how much heat escapes through 1 m² of structure at a 1 Kelvin temperature difference. The lower the U-value, the better the structure insulates and the lower the annual energy loss.
Thermal Resistance (R-Value)Thermal resistance shows how well a structure slows down heat flow. The higher the R-value, the better. Adding insulation increases resistance and lowers heat transfer.
Lambda (λ)Lambda tells how well a material conducts heat. Lower lambda means better insulation. That is why thinner PIR/PUR can perform similarly to a thicker layer of standard EPS or mineral wool.
Thermal BridgesThermal bridges are weak spots such as lintels, ring beams, corners, anchors, plinths or balcony connections. Heat escapes faster there and condensation or mold often appears in these areas.
Dew Point, Moisture and Vapor DiffusionA damp structure insulates worse and can create mold risk. With old buildings, timber frames and internal insulation, always think about where water vapor can travel and where it may condense.
External vs. Internal InsulationIf possible, insulation is usually applied from the outside. Internal insulation is possible, but it must be designed very carefully because of dew point, moisture and mold risk.
How to choose a climate zoneThe climate zone in this calculator is not the lowest winter temperature. It represents an estimated average outdoor temperature during the heating season. A warmer zone gives lower losses, a mountain zone gives higher losses.
Indoor temperature mattersThe difference between 20 °C and 24 °C is not cosmetic. The bigger the indoor-outdoor temperature difference, the more energy escapes. A workshop, garage, bathroom and living room can therefore give different results.
Windows and doors are not just openingsWindow and door areas are subtracted from the wall and calculated using their own U-values. An old window can lose several times more heat than an insulated wall.
Ceiling and roof often decideWarm air rises, so a poorly insulated ceiling or attic can consume a large part of the savings from an insulated wall. The facade alone may not solve the whole building.
Floor and cold cellarA floor above a cellar, garage or ground behaves differently than a wall exposed to outdoor air. The loss is often lower than through a roof, but cold floors strongly affect comfort.
Ventilation and air leaksNot all heat escapes through materials. A lot of energy is carried away by air exchange, drafts, gaps, chimney effect or leaky windows. Older leaky houses can have very high ventilation losses.
Energy price changes paybackThe same insulation pays back differently with electricity, gas, wood or a heat pump. The more expensive the energy, the faster savings appear in money.
Insulation cost should mean the full systemFor a realistic price per area, include insulation, adhesive, anchors, mesh, render, labor, scaffolding and details. If you enter only the board price, the payback will look too optimistic.
When to call a designerCall a designer especially for internal insulation, damp masonry, heritage buildings, timber frames, flat roofs, complex assemblies, subsidy projects or official energy certificates. This calculator is an orientation tool, not a standard calculation.
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