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The thermal insulation in a building is intended to protect its occupants adequately from weather factors. It is also meant to ensure a comfortable indoor climate. For this, it is necessary to thermal and ventilate the rooms according to their usage pattern.
Thermal insulation encompasses, in particular, all measures for reducing heat transmission via the building's enclosing surfaces and partitions to rooms with differing temperatures.
The VST permanent formwork system consists of an in-situ concrete core and cement- bonded particle board on the surface.
The thermal conductivity coefficient of cement-bonded board is specified by the manufacturer as being = 0.26 W/mK. Concrete's characteristic values are defined by the related standard.
A VST structure's general insulation level is therefore established in dependence on the basic materials employed. Cement-bonded particle board generally has better thermal insulation properties than concrete alone; however, an additional layer of insulation is required to achieve contemporary insulation levels.
Thermal resistance
Because fresh concrete poses no risk of damage or impairment to the thermal insulant's properties, this item can be represented by the table below.
| nr. | description of layers | thickness | thermal conductivity coefficient l | R | U |
| [mm] | [W/mK] | [m²K/W] | [W/mK] | ||
| 1 | cement bonded particle board | 24 | 0,26 | 0,092 | |
| 2.1 | concrete core | 102 | 2,30 | 0,044 | |
| 2.2 | concrete core | 127 | 2,30 | 0,055 | |
| 2.3 | concrete core | 152 | 2,30 | 0,066 | |
| 2.4 | concrete core | 167 | 2,30 | 0,073 | |
| 2.5 | concrete core | 182 | 2,30 | 0,079 | |
| 2.6 | concrete core | 202 | 2,30 | 0,088 | |
| 2.7 | concrete core | 252 | 2,30 | 0,110 | |
| 3 | cement bonded particle board | 24 | 0,26 | 0,092 | |
| 1 | overall thickness D= 150 mm | 0,229 | 2,506 | ||
| 2 | overall thickness D= 175 mm | 0,240 | 2,440 | ||
| 3 | overall thickness D= 200 mm | 0,251 | 2,377 | ||
| 4 | overall thickness D= 215 mm | 0,257 | 2,341 | ||
| 5 | overall thickness D= 230 mm | 0,264 | 2,305 | ||
| 6 | overall thickness D= 250 mm | 0,272 | 2,260 | ||
| 7 | overall thickness D= 300 mm | 0,294 | 2,154 |
A perimeter wall is assumed for the purpose of calculating the U-value; furthermore, 0.04 + 0.13 = 0.17 m² K/W (according to DIN EN ISO 6946) is assumed as the rated value of the thermal transfer resistance.
Additional insulation should be installed to achieve the minimum permissible values or higher, desired qualities in accordance with applicable regulations.
Influence of moisture transport on thermal resistance
The possible influence of moisture transport due to surface condensation and internal condensate formation on a wall's insulation properties is to be assessed through calculation.
A test series conducted by the Fraunhofer Institute for Building Physics serves as a reference here.
The influence of temperature and humidity on resistance to water vapour diffusion was studied in the laboratory.
This problem only occurs with perimeter walls, no precipitation of condensate being expected in the interior at normal temperatures.
Because outer walls require thermal insulation to achieve the required minimum values, VST wall constructions always remain in the warm range.
