Almondia – Bautipps Die Bauherrenberatung

It all comes down to optimal roof insulation

If you want to ensure sustainable and energy-efficient insulation of your roof, there is no way around roof insulation. Find out what options are available to you to improve your home’s energy performance and what to consider when deciding to insulate your roof here.

Why good roof insulation is important

Suitable insulation for roofs is essential for various reasons. First and foremost, already continuously rising energy prices provide weighty arguments for the use of the most long-term and cost-effective solution possible with regard to roof insulation. After all, with the help of an optimally insulated roof, energy costs can be saved every year. Subsequently, the rapidly changing climatic conditions during the year create the need for flexible insulation solutions that meet the environmental conditions, for a comfortable living environment all year round. In winter, no homeowner wants cold to penetrate into the living area from the outside, nor should warming heating air get out. In summer, in turn, not too much heat should enter the interior of the house, and air-conditioned premises thus maintain their stable and cool temperature ideally regardless of external conditions. Especially in the attic, these aspects have a special significance. Therefore, as a homeowner or purchaser, you cannot permanently avoid suitable roof insulation.

What must perform roof insulation

Proper insulation of your roof is, first of all, an essential part of the basic thermal insulation to prevent heating losses of your house in winter, as well as to prevent excessive heating of the interior in summer months, that is, roof insulation must ensure air tightness. In addition to this primary insulation function, however, the insulation must also allow diffusion. Moisture must be able to escape to the outside so that condensation caused by heating cycle and room use does not remain inside. This function is performed by a vapor barrier film. If the vapor barrier is missing or incorrectly installed, there is a risk of moisture and possible damage to the roof, which can only be repaired at a higher cost.

The different types of insulation

Insulation of your roof they can do both from the outside and from the inside. However, while external insulation requires re-roofing, insulation from the inside usually means a reduction of the internal surface due to the thickness of the insulation material.

Above-rafter insulation (exterior)

In this variant, the new insulation boards are attached to the entablature after removal of the roofing. The structure and rafters underneath remain freely visible. A vapor barrier is laid in the same breath. Advantageously, the attic can remain inhabited during the reconstruction. The disadvantages are again the high cost of materials and the need for new roofing.

Insulation between rafters (inside)

The insulation itself is done from the inside. Therefore, the roofing does not need to be removed. A subsequent installation is therefore feasible at any time. Anyone aiming to renovate an old building will find this the ideal solution. Here, the insulation material is integrated between the rafters. The advantage is that extensive roof renovation is not necessary, and heating costs are saved in the winter. The disadvantage, however, is that the solution requires a lot of effort, which means that installation costs can quickly add up.

Under rafter insulation (inside)

Those who choose this option, create an additional layer of insulation. Thermal bridges in the area of the rafters are thus subsequently eliminated. Under-rafter insulation can also be used to supplement between-rafter insulation. The advantage here, in turn, is that the costs are still manageable. A disadvantage could be the complete shoring of the rafters, the appearance in this regard is lost. Energy efficiency is increased with the method in the same way as with the other two types of insulation.

The insulating material

Depending on the type of insulation can be used different materials. In addition to insulation material such as mineral wool, rigid foam boards or even polystyrene, for example, chipboard with tongue and groove, battens and vapor barrier film are also used. The use of these and other materials depends on how the particular roof is to be insulated.

Mineral wool is used for under-rafter and inter-rafter insulation. EOS or Styrofoam, in turn, is used for above-rafter insulation. Styrofoam and mineral wool are easy to process, adjust and install. The disadvantage is again that you should wear a mouth guard as well as protective clothing if you are aiming for self-installation. Due to the microparticles that are created, the highest value must be placed on occupational safety in order not to risk lung diseases during processing.

Roof insulation: costs and funding opportunities

Of course, in all questions of planning your roof insulation, the cost factor should not be ignored.

For roof insulation from the inside, costs between 12,000 euros and 20,000 euros are considered realistic nowadays. New roofing is not necessary in this case. When it comes to roof insulation from the outside, again, costs between 30,000 euros and 35,000 euros are the norm (along with the re-roofing that is required along the way).

However, since 2021, various funding opportunities have been available. The renovation subsidy can be obtained after the application with the help of BAFA. The BEG subsidy is applied, which covers individual measures. For those who are still at the beginning of the planning process, we recommend using our Prefabricated house calculator to get a first impression and identify suitable offers.

Structure of the roof insulation

Basically, it is necessary to distinguish between the two options of internal and external insulation of the roof. Both variants have different advantages and disadvantages that have to be weighed up when making a decision, not least in terms of costs, where there are sometimes considerable differences. In conclusion, here are some key points that you should consider when making your decision:

Roof insulation inside

  • Insulation material is fixed between the rafters
  • Installation of the vapor retarder / vapor barrier
  • Support and counter battens are installed with the cladding

Roof insulation outside

  • Rafters form the basis
  • Vapor barrier is attached to rafters
  • On top of this comes the underlayment, counter battens / load-bearing battens
  • Above it takes place the normal roofing

Conclusion: The main advantages and disadvantages of both variants

Advantages and disadvantages of internal roof insulation

+ usually possible without approval
+ cheaper than external insulation
+ especially suitable for half-timbered facades, listed buildings
– Reduction of the interior height
– Insulation losses at rafters
Roof beams no longer accessible

Advantages and disadvantages of the outer roof insulation

+ no measures required in the inner roof space, no spatial restrictions
+ Avoidance of thermal bridges thanks to continuous insulation
+ Installation effort limited to outdoor area, living space usable throughout
– bureaucratic effort: adjustment of building height requires official approval
– Distance areas to possible neighboring properties to be taken into account
– higher cost

Autorin Sarah Völkl

Sarah Völkl hat Architektur studiert und ist seit Jahren das Gesicht von a better place. Mit ihren Videos ist sie bei YouTube vielen Personen schon länger bekannt. Sarah teilt Ihr Wissen jetzt auch bei den Bautipps von Almondia.

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