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Energy requirements for existing cellar ceilings and various basement surfaces

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In the Energy Saving Ordinance (EnEV), requirements concerning existing basement surfaces (that includes walls separating from ground or unheated space, ceilings separating from ground or from outside air below) have to be met only as far as these components are subject of a refurbishment measure described in Annex 3 of the ordinance (“conditional requirements”) or are part of the envelop of an extension (e. g. base of a heated extension). The requirements described below apply to residential buildings and zones of non-residential buildings heated to normal temperatures; for zones of non-residential buildings with set-point temperatures below 19°C different (or partially even no) requirements are valid.

Concerning basement surfaces, Annex 3 lists the following measures as triggers

  • replacement or first-time installation of walls against ground or unheated space (except attics) air as well as of ceilings separating heated space on the lower side from ground or from unheated space; here, a u-value of 0.30 W/(m²·K) is required for the surfaces concerned;
  • installation of outside coverings or sheathings, moisture barriers or drainages on basement surfaces (especially walls against ground); here, a u-value of 0.30 W/(m²·K) is required for the surfaces concerned;
  • installation or replacement of floor constructions (i. e. all the functional layers) on the heated side of a basement ceiling (or ground floor of a heated basement); here, a u-value of 0.50 W/(m²·K) is required for the surfaces concerned;
  • replacement or first-time installation of ceilings against outside air below or installation of sheathings on the cold side of these ceilings; here, a u-value of 0.24 W/(m²·K) is required for the surfaces concerned;

if more than 10% of the basement surfaces of a building (i. e. the sum of all surfaces of walls and ceilings against ground, outside air below or unheated space – except attics) are subject of the measure. A further precondition for all trigger measures is that the components are parts of the envelope of heated space.

Basement components that were constructed or renovated – meeting the energy performance requirements – after December 31, 1983 are excluded from these provisions. In these cases, the legislative authority assumes that the requirement level of the Thermal Insulation Ordinance 82/84 is met: For this assumed level before the measure, the cost effectiveness of an improvement to the U-values required in Annex 3 could not be proven by accompanying studies in general. This does not, however, mean that in individual cases the cost effectiveness cannot be achieved.

If for one of the above mentioned measures the insulation thickness is limited for technical reasons (e. g. because of insufficient height of the room or because of connection to stairs), it is sufficient to install the maximal insulation layer using an insulation material of a maximum thermal conductivity of λ= 0.035 W/Km (WLG 035). If an insulation consisting of renewable material is selected or if the insulation measure is carried out using blow-in technologies, a deviance to a maximum of WLG 045 is permitted.

The requirements are also fulfilled if, after the changes to the building envelope, the requirements of a similar new building according to EnEV (level 2014) are not exceeded by more than 40%.

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