Zum 1. November 2020 hat das Gebäudeenergiegesetz (GEG) das bisherige Energieeinsparungsgesetz (EnEG), die bisherige Energieeinsparverordnung (EnEV) und das bisherige Erneuerbare-Energien-Wärmegesetz (EEWärmeG) abgelöst. Aus diesem Grund wird das Bundesinstitut für Bau-, Stadt- und Raumforschung das Infoportal Energieeinsparung in Kürze an den neuen Rechtsstand anpassen. Die Arbeiten dazu laufen mit Hochdruck. Der neue auf das GEG umgestaltete Internetauftritt wird innerhalb der nächsten Wochen zur Verfügung stehen.

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Retrofit insulation of a pitched roof

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Zwischensparrendämmung bei einem Steildach von der InnenseiteSource: Fotolia

Occasions for a retrofit insulation of a pitched room can be:

  • an extension in the attic
  • a renovation of the roofing or
  • a wish to improve the thermal comfort during winters and summers.

Depending on the set goal and the existing construction, there are different ways to realise a retrofit insulation of the roof.

  • In case of a sufficient dimension of the rafters, the measure can be realised exclu-sively by insulation of the space between the rafters.
  • In course of the renovation of the roofing, a combination of insulation between rafters combined and insulation above rafters is a common variation. This can achieve very good insulation values. As an alternative, the vertical dimension of the rafters can be enlarged using reinforcing battens.
  • If the roofing is kept in place, a combination of insulation between and underneath the rafters is an appropriate choice. This, however, reduces the usable room height of the attic beneath the sloping ceilings.
  • If a heated extension in the attic is not planned in the foreseeable future, the insulation of the top storey ceiling is a suitable alternative.

The achieved energy cost savings of a thermal insulation of a roof also depend on the initial state.

U-values for selected constructions

Among other things, the energy performance of a roof depends on the existing construction. Depending on the age of the building and on the region, a variety of constructions can be found. The age of the building alone only allows a lim-ited inference of the energy quality.

The following table shows exemplary U-values of frequent constructions. Pitched roofs are normally designed as wooden constructions.

Roof
Construction systemYear of constructionStructure of building elementU-Wert W/(m²·K)

Steep roof,

timber structure

until 1948rafter, vented, clay shingle on battens, 1 cm common reed matting, plastered1.96

Steep roof,

timber structure

1949-57rafter, vented, clay shingle on battens, 5 cm wood-wool slab, plastered1.06

Steep roof,

timber structure

1958-68rafter, vented, 4 cm insulation, vented, clay shingle on battens, 2.4 cm formwork, wood-wool slab, plastered0.60

Steep roof,

timber structure

1948-78rafter, vented, 4 cm insulation, vented, clay shingle on battens, 1.25 cm gypsum plaster board, plastered0.95

Source: [Zentrum für Umweltbewusstes Bauen e. V.]

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