Interim savings - what costs do you have to calculate?

If no renovation of the roofing is planned, and yet a loft conversion is to take place, the intermediate rafter insulation is the most economical option for the roof insulation. What an interim insulation with different insulation materials can cost, and which factors are decisive for the price, you read in detail in this article.

prime example

As a prime example, we want to insulate the saddle roof (180 m² roof area) with an intermediate sparing insulation in a 12 x 10 m single-family house. A vapor barrier film is also applied. Additionally we cover the insulated rafters afterwards with Rigips. Our rafter height is sufficient for the required insulation thickness, so we do not need aufzudoppeln.In our example, the rafter portion of the roof area is 12%.

Insulation between the rafters2,355 EUR
vapor barrier1.215 EUR
Plasterboard panel3,675 EUR
Total cost of the project7,245 euros


Details about our insulation and cladding can be found in our service description.

All prices in the article are net prices.


Note that the quoted price example for interim savings is just a prime example. The work can cause significantly higher or lower costs in your house, depending on a variety of individual circumstances.


Intermediate rafter insulation is the simplest solution for insulating the attic. The insulation material is clamped as mats between the rafters. However, it always depends on the local conditions whether a sufficient insulation effect on the roof can be achieved solely by the inter-rafter insulation (the current EnEV requires a maximum heat transfer value of 0.20 W / (m · K) for roof areas). Should this not be achievable in the existing gap between the racks, the rafters must be doubled or an additional under rafter insulation must be installed. Compared to a significantly more expensive Aufsparrendämmung the effect of the Zwischensparsparentifikation is significantly limited and the risk of creating thermal bridges is very large in the Zwischensparparendentämmung.

Basic price criteria for intermediate savings

Rafter part in the roof area

The heat transfer value is always calculated over the entire roof. However, you can only insulate between the rafters. The higher the rafters on the roof surface, the greater the required insulation thickness between the rafters, and thus the insulation is more expensive.


As a rule, almost exclusively mineral wool sprag felts with rated values ​​of 032 or 035 are used for rafter sparing today. The prices for the material in this case are very close to each other, the differences are usually less than 2 EUR per m² in practice

Cost of possibly additional work required


If the inside height of your rafters is not sufficient for the selected insulation thickness, you have to double the rafters. This means that additional wood needs to be fixed to the interior rafters in order to increase the internal height of the rafters. You have to expect around 8 - 11 EUR per meter of rafter length.

additional under rafter insulation

Another possibility for additional insulation is the application of a sub-rafter insulation in addition to the intermediate rafter insulation. Depending on the required board thickness and insulation value, the costs are usually between 30 and 40 EUR per m². If you choose directly plasterable panels, you may be able to save yourself an interior paneling with Rigips.

Additional costs with additional under rafter insulation

In our example, therefore, additional costs of approx. 10 - 20 EUR per m² - ie approx. 1,800 - 3,600 EUR in total should be assumed if a plasterboard panel is removed. Alternatively, you can also perform a cladding with gypsum fiber boards, on which an insulation is laminated. With 60 mm mineral wool insulation, you have to reckon with additional costs of around 5 - 15 EUR per m², with 120 mm insulation with additional costs of around 15 - 25 EUR per m². So this is not necessarily the cheapest alternative, plasterable insulation panels are often cheaper, and also easier to work with.

Conservative factors

  • low rafter content in the roof area
  • sufficient internal height of the rafters (no need for doubling)
  • already good insulating roofing

Increasing factors

  • high rafter share
  • uneven rafter intervals
  • geometrically complicated roof trusses
  • low internal height of the rafters (additional doubling necessary)

Saving opportunities through self-construction or personal contribution

The installation of intermediate rafter insulation and vapor barrier is a classic work for the DIY. However, one should have basic knowledge and some experience, and work very carefully. Even small thermal bridges can cause severe moisture damage and massive mildew, which is usually noticed very late under the paneling.

Saving options for intermediate savings

If you do the intermediate rafter insulation yourself, you only have to bear the material costs. In our example, that would mean that you can save around 5 EUR per m² of roof area. Depending on the rafter spacing and roof shape, the savings can be up to around 8 EUR per m². However, one has to reckon with the fact that the material may be slightly more expensive than a craft company charged, which in turn puts the savings somewhat into perspective.

Saving options when attaching the vapor barrier

If you are a little skilled and work well, you can also apply the vapor barrier yourself. This also brings you a cost savings. Based on our example, you can also save around 5 - 7 EUR per m² for the vapor barrier.

Make interior lining yourself

If you also do the interior lining yourself, you save at least 10 - 13 EUR per m² in addition. Depending on how complex the paneling work, the savings can be even higher.

Total savings on our project

Our - very simply designed - project thus saves at least 25 EUR per m² of the costs of self-construction. In terms of numbers, the total cost of our example project would decrease from € 7.452.22 to around € 2,700, provided you can reasonably purchase the material.


There are a large number of subsidies available for energy renovation and insulation. In addition, you can also write off manual labor in many cases with the income tax return. More information about subsidies and possible depreciation can be found in our general funding overview. Please note, however, that in the case of self-damaging, some subsidies or discounts are not possible.

Tips & Tricks

In any case, have a specialist calculate the required insulation thickness that you need in your case. The deciding factor is not only the thickness of the insulation mats used and the design value of the insulation material you use, but also the rafter content. In the case of intermediate insulation, you must in any case achieve a heat transfer value at the roof that may not be higher than 0.20 W / (m · K).

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