Glossary of insulation terms

Here are some common terms relating to PU insulation.
Remember that you can also consult our main Glossary for all terms used in the polyurethanes business.
Tip! Read more about building insulation at PU and you and in our Construction pages.

Thermal insulation is any substance or material that is used to resist and reduce heat transfer by conduction. Insulation is used in our buildings to maintain a comfortable internal temperature independently of external temperature changes.
The U-Value, also called the overall heat transfer coefficient or thermal transmittance is a measure of how well a material transmits heat over a given area, under standardized conditions. The lower the U-value, the better the insulating ability of the material.  U-value is the reciprocal of R-value.
Based on the U values, an empirical formula gives heat energy expenditure per square metre of external wall or roof during a heating period as approximately:
U value x 10 = litre of heating oil required
Unit: W/(m²K)
Formula: U = 1/R = QA/∆T
R- Value
R-value is a measure of the thermal resistance of an insulation or building material. The R-value depends on the insulation type. The higher the number, the greater the effectiveness of the building insulation. R-value is the reciprocal of U-value.
Unit: m²K/W
Formula: R = ∆T/ QA
K-value refers in Europe to the total insulation value of a building. It is obtained by the total inward surface of the outer walls of the building divided by the volume of the building, multiplied by the average U-value of the outward walls of the building.
Unit: W/(m3K)
λ-value indicates the ability of an insulation or building material to transfer heat by conduction from one side of the material to the other. What is called the k-value or thermal conductivity of construction materials in the US, is called λ-value in Europe.
The lower the number, the better the insulation performance of the material.
Unit: W/(mK)
K45 & E80
K45 stands for the new European norm of building insulation and implies that the total insulation value of a building shell (K value) should not exceed K=0.45.
A house with a volume of 400 m³ and a K-value of 0.45 (K45) will therefore require 180W to maintain its interior temperature 1 K above the exterior temperature. To maintain the house at 20°C when it is freezing outside (0°C), 3600 W of continuous heating is required.
The legislation has been adapted to not only consider the external shell, but also the different internal techniques like heating and ventilation. This is captured with the E-norm (E100; in some countries E80).
Norm: K45 and E100 (or lower)
An E100 building would easily have an energy demand of 1500-2100 € per annum.
Low Energy House (LEH)
A Low Energy House (LEH) is any type of house that, through design, technologies and building products, uses less energy from any source than a traditional or average contemporary house. Low-energy buildings typically use high levels of insulation, energy efficient windows, low levels of air infiltration and heat recovery ventilation to lower heating and cooling energy.
An LEH would normally have an airtight building shell of 1.5 ACH @ 50 P pressure, measured by blower-door test, whereas a traditional house would have a value of 7-8 ACH.
Norm: K32 and E70 (or lower)
An LEH would have a total energy demand for space heating and cooling of air-conditioned area of about 6 to 12 kW/m² per annum (or an average energy demand of 300-500 € per annum).
Passive House (PH)
The Passive House (PH) concept represents today’s highest energy standard with the promise of dramatically slashing the energy consumed by heating buildings. Strictly speaking, it is a building whose energy consumption does not exceed 15 KWh/m² per annum (K15).
The term ‘Passive House’ refers to a specific construction standard for buildings with good comfort conditions during winter and summer, and without a traditional heating or cooling system. A Passive House is a super-insulated, virtually airtight building that is primarily heated by passive solar gain and by internal gains from people, electrical equipment, etc. Energy losses are minimised. Any remaining heat demand is provided by an extremely small source. Avoidance of heat gain through shading and window orientation also helps to minimise any cooling load. An energy recovery ventilator provides a constant, balanced fresh air supply.
Performance characteristics of a Passive House:
1. Airtight building shell ≤ 0.6 ACH @ 50 P pressure, measured by blower-door test
2. Annual heat requirement ≤ 15 kWh/m² per annum
3. Primary Energy ≤ 120 kWh/m² per annum
In addition, the following are recommendations, varying with climate:
1. Window U-value ≤ 0.85 W/(m²K)
2. U-value of roof, wall and floor construction ≤ 0.15 W/(m²K)  (K15)
3. Ventilation system with heat recovery with ≥ 75% efficiency with low electric consumption @ 0,45 Wh/m³ (E45)
4. Thermal Bridge Free Construction ≤ 0.01 W/(mK)
Norm: K15 and E45 (or lower)
A Passive House would have a total energy demand for space heating and cooling of air-conditioned area of about 1 to 3 kW/m² per annum (or an average energy demand of 100-200 € per annum).
You can read more about Passive Houses in our Spotlight section.