With the right roof insulation, homeowners can save energy and thus money. Refurbishment is often urgently required, especially on old roofs. Mathias Klement, an expert at Aroundhome, explains what you should pay attention to and what costs you will have to face.

German roofs are poorly insulated. The consequences: It is heated and burned for what it takes. This not only heats up the climate, but also burns a hole in your wallet. It is therefore an advantage to think about the right roof insulation.

Roof work is difficult to carry out in winter, so the warm season is ideal for renovation work. Before you jump into work, however, take a moment to plan. And watch out: You can get support, especially with financing.

Different types of insulation – different advantages

Not all roof insulation is created equal. In addition to the material and insulation thickness, there are major differences in the type of installation. There is no panacea here, but different advantages and disadvantages that must be weighed up. And of course in the end it is also a question of money.

Above-rafter insulation                                                    

With above-rafter insulation, the insulation material is placed above the wooden structure of the roof. This wooden structure, called a rafter, lies directly under the roof tiles. The problem: the bricks have to be covered. That can be very expensive. Nonetheless, over-rafter insulation is the most efficient way to save heating costs because it has one advantage: there are no thermal bridges. These are small gaps between the wooden rafters and the insulation material through which heat is lost.

Already knew? Because heat escapes through the poorly insulated cold spots in the outer shell of a building, experts call them thermal bridges – not cold bridges, as some believe.

Between the rafter insulation

The insulation between the rafters is, as the name suggests, installed between the rafters. In addition, it is glued with a vapor barrier film. The advantage: the roof does not have to be re-tiled. The work can be done from the inside. But there is also a major disadvantage: thermal bridges can arise. Even specialist companies can often not completely prevent thermal bridges, as Stiftung Warentest has found. Thermal bridges should not only be avoided in terms of energy efficiency. In the worst case, the cold spots can attract moisture and cause mold.

Under-rafter insulation

In order to avoid thermal bridges, it is worth combining between-rafter insulation with under-rafter insulation. Here, insulation material is attached from the inside under the rafters. This prevents gaps in which heat can escape. This in turn increases energy efficiency. Older houses that already have insulation between the rafters can be renovated inexpensively in this way. The only disadvantage: by installing it under the rafters, the living space is reduced by a few square meters.

Do it yourself or hire experts?

When building a new building, you are often already in contact with a roofer who can give you a recommendation and advise. Nevertheless, one should not go into a conversation uninformed. In the case of a roof renovation, many consider trying their hand at home improvement in order to save costs. You should be careful here, because small mistakes can be expensive in retrospect.

What does it cost me?

Protecting the environment and saving money, that’s all well and good, but: Roof renovations are not cheap. The costs are calculated based on the roof size. With above-rafter insulation, the square meter costs € 70 to € 120, with between-rafter insulation between 50 and 80 euros and with under-rafter insulation between 30 and 60 euros.

In order to estimate what costs you will have to face, the roof area must be calculated. This is the most important size for the roofer. The roof area is calculated from the base area, in combination with factors such as the roof pitch, the shape and the overhang. These elements complicate the calculation, so a specialist company can do this for you. Alternatively, you can use an online calculator.

However, it does not make sense to decide which type of insulation to choose based on the renovation costs. Refurbishment for efficient insulation can pay for itself over time. The following sample calculation is based on a building that is often found in Germany: a detached, unrenovated single-family house built in 1973, with 140 square meters of living space and a pitched roof (roof pitch 45 °). The roof is still in its original condition, i.e. it has not been renovated since 1973.


Example between rafter insulation:

In order to meet the requirements of the Energy Saving Ordinance (EnEV), the insulation between the rafters must be at least twelve centimeters thick. The costs for this are around € 13,000. The annual energy cost saving is € 700. This would amortize the investment after around 20 years. However, the next renovation may already be pending. It should also be noted that thermal bridges can arise.

Example of above-rafter insulation:

Even with roof insulation from the outside, the insulation layer must be at least twelve centimeters thick. The costs for the above-rafter insulation are significantly higher, as the roofing also has to be renewed at the same time. This is why above-rafter insulation costs € 30,500. The annual energy cost savings are also around € 700 here. Attention: The costs for the renovation will not be amortized with the savings in the following years.


When calculating costs, it should be noted that the larger and older – and therefore poorly insulated – the higher the savings in energy costs. The energy price is also expected to continue to rise in the next few years. This ensures that the energy savings become more and more lucrative over time. In addition, the measures lead to a considerable increase in the value of the building.

The Kreditanstalt für Wiederaufbau (KfW) recommends: “Energy-related construction measures are complex. It therefore makes sense to call in an energy efficiency expert when building, converting and renovating. This specialized energy consultant ensures the quality of the work – from planning to implementation. And: You definitely need it if you want to apply for KfW funding . Good to know that you will receive an extra grant of up to 4,000 euros for his construction supervision. “

Have you already applied for funding?

Efficient roof insulation increases the energy efficiency of your home, thereby potentially protecting the environment. Renovation measures on the roof insulation are therefore eligible for funding from KfW. There are two options here: credit or grant.

The loan “ Energy Efficient Renovation ” is a low-interest loan with a negative APR of z. B. -2.43%. Thanks to a repayment subsidy, your loan debt is reduced and the term is shortened. So you pay back less than you took in.

The second option is the investment grant 430. This was increased on 01/01/2020. Now there is financial support of up to 48,000 € for the renovation to the “KfW Efficiency House” or up to 10,000 € subsidy for individual measures.

Well prepared is half renovated

If you can hardly wait and want to continue saving, you can prepare the renovation of your own roof yourself. Detaching the antennas, removing the snow guard and sweeping the rafters is quick and easy. This saves you craftsman costs and at the same time you can practice as a do-it-yourselfer.