What is a thermal barrier

Thermal insulation: tips for energetic renovation


Is it even worth insulating?

With an uninsulated house, you literally heat out the open window. About 20 percent and more of the heating energy escape through uninsulated walls and roofs. The uninsulated basement ceiling loses another 5 to 10 percent. That adds up quite a bit. If you wrap your house well with insulation, you not only save on heating costs, but also gain significantly in living comfort. In winter it stays comfortably warm, without drafts and cold walls. And in summer, the insulation helps keep the heat outside, especially under the roof. If the windows are also replaced or provided with new glazing, homeowners can calmly look forward to the next winter or summer. And look forward to the secured building structure and the increase in value of your house.


With our renovation calculator, you can easily calculate whether thermal insulation is worthwhile for your building. You can also determine the savings potential of a renovation and draw up a cost-benefit assessment.

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What is good thermal insulation?

Heat always flows where it is colder. Outside in winter, inside in summer. Heat flows through components such as brickwork, windows or roof. The "U-value" describes the heat transfer through a component. It indicates the thermal output that flows through a component with an area of ​​one square meter, with a temperature difference of one degree between the two sides of the component. The U-value is measured in watts per square meter and Kelvin W / (m²K). The better the thermal insulation, the lower the U-value. For facades, the U-value required by EnEV 2013 is 0.24 W / (m²K). In many unrenovated buildings, the U-value of the outer wall is 1.5 to 2 W / (m²K). A good thermal insulation of the facade nowadays easily achieves a U-value of less than 0.2 W / (m²K).


What can you insulate in the house?

The entire building envelope, i.e. the roof or attic, facade and basement ceiling should be insulated according to today's standard. The following areas can be insulated on the house:


1. Insulation pitched roof

The pitched roof with different roof pitches is the typical roof structure. If a roof is more than 20 years old, modern insulation is recommended. If the attic space is not used, insulating the top floor ceiling is the simplest and cheapest solution. A distinction must still be made here as to whether the attic should be accessible or not. The attic insulation can also be carried out by experienced do-it-yourselfers. However, if the attic is to be used as living space, the sloping roof and possibly the ceiling must be insulated from the loft.

There are basically three options for thermal insulation of the roof:

  • Most often, the insulation is carried out between the rafters. In most cases, the rafter thickness is not sufficient to install the recommended insulation material thickness of 20 centimeters. This can be remedied by doubling the rafters.
  • Under-rafter insulation is the ideal complement to between-rafter insulation and helps to further increase energy efficiency. Under-rafter insulation reduces thermal bridges in the area of ​​the wooden rafters, which have a 3-4 times higher thermal conductivity than the insulation between the rafters. In addition, under-rafter insulation can serve as an installation level in which all necessary cables and lines are laid.
  • If the roof is re-covered, above-rafter insulation is recommended. Here the new insulation lies outside on the rafters. The above-rafter insulation is a task for an experienced specialist company.

Older roofs often have a U-value of 1.0 W / (m²K) or worse. Newly insulated roofs reduce the U-value to 0.20 to 0.15 W / (m²K). So they insulate five to almost seven times better.


2. Insulation of the outer wall

In older houses, facades often have a U-value of 1.2 W / (m²K) and more. In comparison, a well-insulated wall now has 0.2 W (m²K). In comparison, uninsulated walls lose up to six times more energy when heating.

Additional advantage of thermal insulation: On the inside of insulated facades, the wall surfaces remain significantly warmer than before. This makes it much more comfortable and there is no longer any condensation. Continuous insulation also eliminates thermal bridges on which mold can form. Under no circumstances should new windows be built into an inadequately insulated facade. Otherwise, mold can develop from new windows in old walls. It is advantageous to carry out both renovation measures at the same time. In connection with the correct ventilation, mold then no longer has a chance. A thermal insulation composite system (ETICS) is most often used as insulation on facades. Here, insulation boards are glued to the old plaster or - depending on the substrate - also dowelled.

This is followed by a thin layer of mortar in which a reinforcement mesh is embedded in order to absorb tensile stresses and avoid cracks. This is then followed by a plaster as a top coat. Houses with double-shell masonry can be retrofitted with core insulation. The air layer between the two walls is about 6 to 8 centimeters. Insulation material is then blown in through small holes in the outer wall. The cost is around 20-25 euros per square meter. The work is carried out in 1-2 days. Curtain-type, rear-ventilated facades in older houses usually have wooden shingles or slate as weather protection and are rarely insulated. They can then be insulated when the curtain shell is removed and replaced. Here the cost of the insulation (approx. 20 to 30 euros per square meter) is significantly cheaper than for the new curtain, which can consist of natural wooden cladding, for example.


3. Thermal insulation of the outer wall from the inside

If the facade should or must be preserved, interior insulation is the alternative. An insulation thickness of 6 to 8 centimeters is sufficient. This saves around 10 to 15 percent of heating energy. Correct sealing is important for insulation from the inside. A vapor barrier must be installed if the insulation panels do not take on this function. To avoid structural damage, facade insulation (inside or outside) should be carried out by a specialist company.


4. Insulation of the basement ceiling

The insulation of the basement ceiling ensures warm feet and lower heating costs. The easiest way is to glue or dowel insulation panels in the basement to the underside of the ceiling. The U-values ​​of the basement ceiling in older houses are mostly over 1.0 W / (m²K). Today, U-values ​​of 0.3 W / (m²K) or better are possible. The limiting factor is often the low headroom in the basement, which can be compensated for by using higher quality insulation materials (lower insulation material thickness).