General Information on the Insulation of Roofs
A roof defines the upper limit of a building.
It protects the building and its inhabitants against the effects of rain, wind, cold and heat. Especially old buildings loose a lot of heat through the roof. For this reason the roof is normally the first part of a building to be renovated. There are three ways of insulating a roof: The insulation below, between or on top of the rafters.
The insulation on top of the rafters has the advantage of avoiding thermal bridges and to allow a very thick insulation. A disadvantage is that a refitting requires a substantial effort. The insulation between the rafters has the advantage of being easy and time-saving to fit. However, this kind of insulation is not as effective as the insulation on top of the rafters, because the rafters act as thermal bridges. The insulation below the rafters has similar advantages (easy installation) but has the disadvantage of considerably reducing the available attic space.
Requirements of Roofs
The EnEV requires all roofs and ceilings which separate heated rooms from outside air to have a u-value of 0.30 W/(m²K).
This applies to new buildings as well as to the refitting of insulation. Exceptions are only allowed if this value cannot be obtained due to the thickness of the rafters or an interior lining (see attachment 3, table 4.1) At the same time the EnEV has certain requirements concerning the wind-tightness (from outside) and air-tightness(from inside) in order to limit heat loss.
According to DIN 4108-2 a thermal conduction resistance of > 1.20 m²K/W has to be achieved.
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