Core insulation

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The core insulation is the full insulation between two masonry walls with double-shell external masonry (front and back wall), constructions with curtain-type concrete slabs, house partition walls or between rafters ( insulation between rafters ) in the roof area - without the otherwise necessary air gap of at least 10-80 mm, which is the ventilation / Drying is used and without ventilation openings above and below - designated. The so-called “finger gap” (approx. 1 cm) is also omitted here.

Insulation materials

Solid materials such as polyurethane rigid foam (PUR / PIR), rock or mineral wool , extruded polystyrene rigid foam (XPS), expanded polystyrene rigid foam (EPS) or bulk material can be used for insulation in new buildings . Polyurethane in- situ foam , rock or glass wool, expanded polystyrene granulate (EPS), light-weight silicate foam granulate (SLS20), expanded perlite and airgel can be used for subsequent core insulation . The insulation materials must be permanently water-repellent ( hydrophobic ) and comply with the standardized application of DIN 4108-10 (WZ = insulation of double-shell walls, core insulation). The distance between the shells is limited to 150 mm. Larger shell spacings (currently regulated up to 200 mm) require air-layer anchors with building authority approval.

The reference values ​​of the Energy Saving Ordinance (EnEV 2009) of U ≤ 0.28 W / (m² · K) can already be met with 10 cm core insulation with a thermal conductivity of 0.035 W / (m · K). To meet the Passive House criterion of U ≤ 0.15 W / (m² · K), significantly better thermal insulation materials are required, possibly in combination with increased shell spacing, e.g. B. 20 cm core insulation of thermal conductivity 0.032 W / (m · K).

In the case of core insulation, according to DIN 1053, drainage openings are to be arranged in the base area of ​​the outer shell (5000 mm² per 20 m² wall surface). If the facing masonry is carried out correctly, no tracks (i.e. no water leakage) from the drainage openings can be found in practice. In the case of plastered facing walls, the drainage openings must be closed before plastering in order to prevent them from clogging with the plaster.

Board insulation materials can be used for core insulation in new buildings.

Subsequent core insulation

The subsequent core insulation in the existing building is possible with blow-in insulation materials or in- situ foam . The insulation material is introduced through holes drilled in the outer wall. A distinction must be made between pourable and fibrous products. The installation of pourable products, e.g. B. EPS granules, expanded perlite, lightweight silicate foam granules and airgel, requires few and small injection holes. The materials are distributed very well in the hollow layers. These products are predestined for the insulation of narrow hollow layers (up to 5 cm), for the optimization of rear-ventilated facades and post-insulation of exposed exposed aggregate concrete facades with rear-ventilated core insulation. However, as trickling through can occur, leaks should be identified and sealed using a smoke machine before the measure is taken. In the case of larger hollow layers, fibrous products, e.g. B. rock and glass wool can be used. These are more cost-effective and interlock with one another and with the masonry. Therefore, trickling through does not pose a risk. EPS insulation granulate can also be subsequently solidified with hot steam to prevent trickling out of masonry openings. However, there is no building authority approval for the solidified granulate.


  • Inexpensive compared to subsequently applied insulation layer ( generally ETICS ), i.e. H. shorter payback times
  • short construction times, often 1-2 days for a 1-2 family house
  • there is no loss of living space, nor does the look of the house change.
  • The subsequent core insulation of double-shell masonry, storey ceilings and intermediate rafters meets the requirements of EnEV 2014 if insulation materials of thermal conductivity group 0.40 or better are processed
  • The introduction of bound EPS granulate is new. This approved process ensures a stable connection between the pearls in the hollow layer. The EPS insulation material can no longer trickle out. Windows can then be exchanged or breakthrough work can be carried out.


  • The thickness of the insulation material is limited to the width of the existing space in the double-shell outer masonry (max. 15 cm according to DIN EN 1996). Larger shell spacings are possible with anchors in accordance with general building authority approval. The use of high-performance insulation materials such as airgel or in-situ polyurethane foam is another way of reducing the U-value of the wall.
  • Thermal bridges such as window reveals, wall anchors or brick connections of the double-shell masonry can be better minimized with ETICS .
  • Should water penetrate into the insulation layer, e.g. If, for example, a pipe lying in the wall breaks, drying will be difficult - especially when using mineral wool because of the capillary effects, here EPS insulating granulate offers decisive advantages.
  • In the event of later wall openings or work on the masonry, free-flowing blow-in insulation, such as EPS beads, will leak if this is not solidified, so that the blow-in insulation must then be partially replaced.

Individual evidence

  1. a b A. Drewer, H. Paschko, K. Paschko, M. Patschke: Thermal insulation materials: compass for selection and application. Verlagsges. Müller, 2013, ISBN 978-3-481-03094-0 , p. 89 ff.


  • Retrofitting core insulation without risk (PDF; 1.1 MB) . Results of the 2nd information circle on building renovation on February 4, 2000 - as part of the impulse program for thermal building renovation in Schleswig-Holstein.
  • A. Drewer, H. Paschko, K. Paschko, M. Patschke: Thermal insulation: compass for selection and application . Verlagsges. Müller, 2013, ISBN 978-3-481-03094-0 , p. 89 ff.