Retrofit insulation of a pitched roof
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 system||Year of construction||Structure of building element||U-Wert W/(m²·K)|
|until 1948||rafter, vented, clay shingle on battens, 1 cm common reed matting, plastered||1.96|
|1949-57||rafter, vented, clay shingle on battens, 5 cm wood-wool slab, plastered||1.06|
|1958-68||rafter, vented, 4 cm insulation, vented, clay shingle on battens, 2.4 cm formwork, wood-wool slab, plastered||0.60|
|1948-78||rafter, vented, 4 cm insulation, vented, clay shingle on battens, 1.25 cm gypsum plaster board, plastered||0.95|