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Thermal Insulation

Thermal insulation is the most crucial and effective but at the same time the cheapest way to achieve environmentally friendly living. This applies to both new buildings and re-constructions, and it will also be saving heating costs for the rest of your life. Here you can get more detailed information about thermal insulation.

Thermal insulation of building materials

1. Thermal insulation

Thermal insulation will keep your house warm in winter. In summer when temperatures outside are much higher than inside, good thermal insulation keeps the air cool inside the house.

2. Thermal insulation in comparison

The diagram (available in German only) shows that special thermal insulation materials are much more efficient rather than building materials in providing thermal insulation. The thermal insulation effect of concrete, for example, is 80 times worse than of the thermal insulation material Austrotherm TOP®/XPS®. Therefore it is very important that the coldness can not penetrate unhindered inside the house via concrete balcony, roofs or basement walls. Although softwood is famous for its good insulation properties, it is 4 times worse than Austrotherm EPS®.

Therefore, it becomes generally accepted to divide building materials into two groups: building materials for load transfer and building materials for thermal insulation. Nowadays more than 6 million square metres per year of façades in Austria are made with composite thermal insulation systems. The insulation thicknesses, which are usual today, amortize at very short time. But the houses should not be insulated only because of the building regulations or the eco-subsidies; they should be specially good insulated because of ones who live in them.

3. Thermal conductivity [W/mK]

The thermal conductivity describes the heat conduction of building materials. Smaller the value, lower the heat conduction and better the thermal insulation of the material.

The nominal value of the thermal conductivity is generally used during the planning of building units. For the determination of the thermal conductivity the thermal conductivity of a building material at 100 °C in dry condition is ascertained in a lab (10,tr).

The thermal conductivity indicates amount of heat (Q) that goes through 1m thick homogenous building material per second and square metre when the temperature difference between the warmer and the colder side is 1 °C. The physical unit is measured in [W/mK].

Thermal insulation of constructional elements

Walls, ceilings and floors are generally composed of several building materials (walling, thermal insulation, plaster, etc.). To determine the complete thermal insulation of a constructional element the thermal insulation properties of the single building materials with its thicknesses and the so-called heat transfer resistance at the surface of the constructional element (inside, outside) have to be considered.

1. Heat transfer resistance R_si, R_se [m²K/W] (former 1/a)

Before the heat of the air can go into (or can leave) a constructional element (floor, ceiling, wall), the so-called boundary layer has to be penetrated. The boundary layer causes resistance to heat penetration. The main factors of this process are the strength of the air motion and the position of the surface of the constructional element. Outside the building the air motion is strong and heat transfer resistance is small. On the contrary, inside the building there is only slight air motion, and as a result the heat transfer resistance value is large. For example, the difference between the room temperature and the wall surface temperature is the consequence of the heat transfer resistance. The heat transfer resistance of walls, ceilings and floors in Austria is regulated by the standard OENORM EN ISO 6946.

Examples of the heat transfer resistance R_si + R_se:

Constructional element	R_si + R_se [m²K/W]
External wall	0.17
highest floor ceiling, externally insulated roof (heat flows upwards)	0.14
Ceilings above outside air (heat flows downwards)	0.21
intermediate ceilings	0.26

2. Heat transfer coefficient U-value [W/m²K] (former k-value)

The U-value states the amount of heat which flows through a constructional element per second and square metre, when the temperature difference between both sides is 1 °C. The U-value is calculated by making the reciprocal value of the total of the heat transfer resistance (R_si, R_se) and the quotient thickness of building material and thermal conductivity. The U-value is necessary for the calculation of heat losses through the constructional elements of a building.

Note: U-values must not be added!

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