Blow-in insulation - fast, efficient and cost-effective

Blow-in insulation is an efficient and cost-effective form of thermal insulation. It plays a role especially in old building renovations. The insulation material is blown through previously drilled holes in the facade, ceiling or floor. For this purpose, the presence of a cavity - ie a two-shell construction structure - required.

Blow Insulation: Cost-effective and fast

Blow-in insulation is suitable for many areas of the home and is extremely cost-effective compared to other types of insulation. The advantages of blow-in insulation also include the quick, uncomplicated application of the insulating material - as a rule, the insulation work is completed within one to two working days. Depending on the area of ​​application, the energy efficiency of a house can be improved by up to 30 percent through blown insulations. A structural problem is mainly thermal bridges, which can hardly be completely avoided in this form of thermal insulation.

Table 1: m2 costs for blown insulation in different areas of the house

house areaCost per m2 (EUR)
Insulation of the top floor ceiling15 – 25
Sloping ceilings - Insulation with insulating bag50 – 65
Sloping ceilings - blown insulation with hardboard system40 – 50
Flat roof insulation20 – 40
Core insulation of the facade15 – 30
Basement ceiling insulation15 – 25
Subsequent filling of beam constructions50 – 70

Workflows for a blow-in insulation

Before commencing insulation work, a skilled tradesman analyzes the condition of the parts of the building to be insulated with blown insulation. He checks whether existing cavities are suitable for Einblasdämmung, alternatively, they can also be created by a wooden structure. Especially before a core insulation of the facade an endoscopic examination is made to determine the width of the cavity. Then the grid for the injection holes is determined. These are between two and three centimeters in size and are placed so that the insulation material reaches all areas of the cavity well. In addition, the expert makes a decision about the insulating material to be used. In addition to the insulating effect, other factors play a role here as well - diffusion openness and capillary activity, moisture resistance, requirements for sound and heat insulation and the fire protection properties of the insulating layer.

Blowing with hose and packer

The blowing of the insulating material is carried out with a hose which is connected to a so-called packer. During the blowing process, the material is compressed, so that air bubbles can not be achieved. After complete filling of the cavity, the injection holes are closed. Then the surface can be plastered, painted or clad.

Tips & Tricks

With the exception of the insulation of the top floor ceiling, blow-in insulation should always be carried out by a specialist tradesman. Among other things, his tasks include determining whether a domestic area is suitable for blow-in insulation, the professional preparation of the insulation room and the choice of insulation materials. Even an improperly executed insulation may prove to be a problem later - for example due to wrong choice of insulation or insufficient compaction of the material.

Blow-in insulation of the top floor ceiling

A thermal insulation of the top floor ceiling takes place when the attic is not used for residential purposes. Blow-in insulations can be made here in two different forms:

  • Classic blow-in insulation: The compartments between the load-bearing beams are filled by the blow-in insulation. Above this is either an existing floorboard or the floor of the roof truss will be rebuilt. In a concrete ceiling without a cavity, the space required for the insulation can be created by a construction of wood and OSB boards.
  • Loose blow-in insulation: If the top floor ceiling is not to be used, the insulation material can be blown into the open compartments without a cover. In order for the roof truss to be inspected for maintenance purposes, the necessary routes are constructed.

Insufflation insulation of the sloping ceilings with insulating bags or hardboard system

Possible variants of a blow-in insulation of the roof slopes are:

  • Insulating sacks: For this purpose, insulating sacks in the form of foil hoses are inserted into the compartments between the rafters. By inflating with air, they adapt to the compartments. Then an insulation material is injected into the bags, which is completely compressed and thus permanently settling is.
  • Hardboard systems: For such insulation, an additional roof battens is applied to the rafters in order to create a rear ventilation level for the roof skin. On it perforated hardboard are mounted. The perforation allows the removal of moisture from the insulation layer, the plates also ensure that the insulation is not pressed against the roof tiles. The insulating material is injected seamlessly into the space between hardboard and inner wall paneling.

Flat roof insulation by means of blow-in insulation

In a flat roof insulation, the insulating layer is blown into the cavity between the roof and the living room ceiling. If no vapor barrier is integrated on the room side, a rear ventilation level of approximately 15 cm must be created in order to discharge the resulting condensation water from the insulation layer. In the presence of a vapor barrier, the insulation material can fill the entire cavity.

Core insulation (hollow wall insulation)

A core insulation or hollow wall insulation in older buildings is almost always made in the form of blowing insulation. Two-shell facades were in use since the turn of the 19th to the 20th century. The outer wall shell is used for weather protection, the inner shell should - initially without insulating layer - improve the thermal protection. The cavities of bivalve exterior walls of old buildings are usually between 1.5 and 12 cm wide. A subsequent core insulation can be made from a cavity width of 3.5 cm. In such very narrow cavities, however, a thermal insulation composite system (ETICS) or a combination of core insulation and ETICS is usually the better solution to sustainably optimize the energy efficiency of the building.

Blow-in insulation of the basement ceiling

For the thermal insulation of the basement ceiling, blow-in insulation is by far the simplest and cheapest solution for thermal insulation. Without additional construction, it is possible if the ceiling has a sufficiently large cavity. Usually it is made from the ground floor. If the cavity is too narrow for sufficient insulation or the basement ceiling has many thermal bridges, a wood frame base on the basement side can form the basis for blow-in insulation.

slot insulation

A building can have numerous cable, pipe, air, maintenance and installation shafts. Insulation of such shafts is important on the one hand because they form thermal bridges, on the other hand, blowing insulation with a refractory insulating material optimizes the fire protection properties of the building. Shaft insulations can also be important for better sound insulation. Pipe and cable ducts can be perfectly insulated by blow-in insulation, while air ducts and maintenance ducts are more suitable for insulation with insulating mats.

Blow-ins in shafts - a job for experts

Blown insulating materials such as mineral wool fibers or perlites adapt themselves to the contours of the shaft, so that the insulation itself can be very uncomplicated. However, above all fire protection reasons, shaft insulation must always be carried out by experts who have received special training for this purpose.

Insulation materials for a blow-in insulation

As insulating materials for a blow-in insulation numerous materials come into question. They must be permeable and capillary active in order to actively regulate the moisture exchange. In house areas with relevant moisture load, they must also have hydrophobic (water-repellent) properties. Insulation materials of building material classes A1 or A2 (non-flammable, only a small proportion of flammable substances) also optimize the fire safety of the house. Blow-in insulation can be done either with granules or with fiber insulation. In addition to mineral and synthetic materials, natural insulating materials can also be used very well for such thermal insulation. Especially for core insulation also so-called local foams made of plastics come into question.


Granules for Einblasdämmungen consist for example of silicate lightweight foam granules, perlite, expanded clay or EPS / Styrofoam. An innovative and particularly high-performance insulation solution here are so-called aerogels, which, however, are also correspondingly expensive. Granules require only a few and small injection holes, spread very well and are therefore ideal for narrow cavities. A disadvantage of blow-in insulation with granules can be trickling in later wall breakthroughs or other injuries of the cavity walls, which make improvements to the insulation required.

fiber insulation materials

Compared to granules, fiber insulating materials are usually the cheaper solution. They are particularly suitable for blowing insulation in larger cavities. Compared to granules, they can be condensed to a significantly higher degree. In all dry house areas also insufflations with natural fibers are possible. Most commonly cellulose and mineral wool fibers (glass or rock wool) are used. There is no danger of scratches on fiber insulation materials - the material fibers become entangled with themselves and with the wall.

Table 2: Selected insulation materials for blow-in insulation

insulationThermal conductivity (W / mK)Minimum insulation thickness (cm)Cost / m2 (EUR)
glass wool0,032 – 0,0401410 – 20
rock wool0,035 – 0,0401410 – 20
EPS / Styrofoam0,035 – 0,045145 – 20
perlite0,04 – 0,072020 – 45
expanded clay0,1 – 0,187218 EUR / 50 l
cellulose0,04 – 0,0451610 – 20

Requirements of the EnEV 2014 for blow-in insulation

The basic requirement of the Energy Saving Ordinance (EnEV) 2014 for the thermal insulation of residential buildings is to achieve at least a heat transfer coefficient (U-value) of 0.24 0.24 W / m2K. For cellar insulation including the insulation of the cellar ceiling, a minimum value of 0.30 W / m2K applies. With regard to blow-in insulations, however, a privilege was enshrined in the EnEV 2014: In the case of energy-efficient renovation, a building is considered sufficiently insulated by this method if the insulation material completely fills an existing cavity. On the other hand, the requirements of the EnEV 2014 are valid without restriction for new buildings that are to receive blow-in insulation, for example as the core insulation of a double-skinned, ventilated facade.

Public funding

Like all other insulation measures, injection insulation can also be publicly funded by a loan or building grant from KfW. Prerequisites for this are the expert opinion of a professional energy consultant as well as an insulation performance above the minimum requirements of the EnEV 2014.

Tips & Tricks

Thermal bridges can hardly be avoided with blow-ins. By appropriate pretreatment of the cavity surfaces - for example, the sealing of joints - and the insulation of window openings and connections can minimize their impact. In the analysis of the building structure before the beginning of the insulating work, the specialist should necessarily check such sites separately.

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