Things to know about interior insulation and construction physics

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Inside insulation is an alternative or supplement to retrofitting outside insulation and/or core insulation. Whilst in these systems the supporting masonry lies on the warm side of the insulation, which means it is usually physically uncritical, the potential or risk of condensation should always be taken into account. There are usually two decisive reasons for using inside insulation and improving the thermal protection:

  • The above-mentioned other possibilities for the arrangement of insulating layers are not possible or inadequate. For instance, in the case of older buildings that are used and heated, where it is neither permitted, desired or economically viable to change the façade view, inside insulation is often the only way to reduce the transmission heat loss.
  • Entire buildings or individual rooms are only used and heated occasionally. This applies e.g. for meeting rooms, ball rooms or sport and hobby rooms. Inside insulation offers decisive energy-saving benefits here. Fast, effective heating is possible because the solid external walls do not need to be heated due to the insulation applied on the inside.

Architects and engineers that were trained before or in the 1990s, often associate inside insulation with constructional damage. The were taught that dew can form in constructions with inside insulation by means of comparative calculations of walls with outside and inside insulation using the Glaser procedure. The solution then was: Careful planning and conscientious installation of inside insulation only in combination with interior vapour proof barriers and retarders.

However, part connections and openings, and also deformations (e.g. beam ends of wooden joist ceilings) represent a problem that is difficult to solve. The positive effect of preventing water vapour diffusing into the inside of the part and therefore condensation through films and/or vapour inhibitors is offset with a reduction of the drying potential for e.g. for moisture penetrating from outside. The summer process of drying moisture toward the inside of construction exposed to driving rain is obstructed by part layers with a high vapour diffusion resistance which can lead to a build up of moisture in the wall cross-section.

In contrast to system structures with vapour proof barriers or inhibitors, the properties of capillary-active inside insulation systems allow longer-term drying, even of previously damaged parts due to the retention of the drying potential. The creation of condensation is accepted because the capillary activity ensures fast and large-scale return of the moisture throughout the entire year. During the past decade, the group of capillary-active insulating materials has proven the most ‘application-safe’ for inside insulation.

The multi-dimensional calculation programs that have been available for some years and are now extremely well calibrated and are used to simulate the thermal and hygric behaviour of façade constructions prove this impressively.

  • Vapour barrier and inhibiting systems
  • Capillary-active systems
  • Information about system selection
  • Requirements with regard to the processing
  • Inside insulation of parts that have contact with the ground
  • Ordinance on thermal insulation (WSchV) / German energy conservat
  • Requirements acc. to EnEV
  • Company declaration about compliance with the EnEV requirements
  • Greenhouse gases
  • Heat transition coefficient (U-value) / heat transmission coeff
  • Overall heat transfer coefficient (R si and R se)
  • Overall heat transfer coefficient (R T)
  • U-value calculation [iQ-Lator]
  • iQ-Lator - principles