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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.

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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