The requirements for the external walls of the building relate primarily to thermal insulation. The construction law specifies, that buildings and installations in buildings should be designed so, that the amount of thermal energy needed for heating is kept reasonably low.
For single-family houses it is calculated (alternatively):
– heat transfer coefficient for walls U [ In / (m² x K) ]
(in the previous standards denoted by the letter k),
– seasonal heat demand indicator E.
Maximum heat transfer coefficients U [ In / (m² x K) ] for a single-family house they are for different types of partitions respectively:
o external sandwich walls with insulation = 0,3,
o single-layer external walls = 0,5,
o internal walls separating heated and unheated rooms = 1,0,
o flat roofs and ceilings under unheated attics with a temperature of. greater than 16 ° C = 0.3,
for flat roofs and ceilings under attics with a temperature of. less than 16 ° C = 0,5,
o ceilings above unheated cellars = 0,6,
about the windows, balcony doors and non-opening glazed surfaces in rooms with a temperature of 20 ° C = 2,6 (I II, III climatic zone)2,0 (IV, V zone),
o drzwi zewnętrzne wejściowe do budynku = 2,6.
The E index is calculated as the ratio of the seasonal heat energy demand to the volume of the heated part of the building. This indicator must not exceed the limit value, which depends on the ratio of the area of all external partitions (including the roof) the heated part to the volume of the heated part.
The E index describes the thermal properties of a building better than the U-value. Two buildings with the same U-values for the walls, may have different heat requirements; the building is more fragmented, with more external walls it will always be "colder".
Moisture is related to thermal insulation – the presence of moisture in the building material increases the thermal conductivity coefficient, which is associated with greater heat losses in the building. Moisture in the material must be taken into account when calculating the heat flow.
Temperature distribution in a brick wall without thermal insulation and in a wall with a heat-insulating layer:
The temperature curve in the insulated wall will be sharp at the border with the insulation. Means, that the entire wall is heated and gives the accumulated heat to the interior. This delays the cooling of the interior, even if the heating is switched off temporarily. The surface of the wall is approx 5,6 ° C higher than in the case of monolithic masonry, which causes a smoother air circulation in the interior.