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 inter-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.

Sample example

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

All prices in the article are net prices.


Please note that the quoted price example for an interim saving is only 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 rafter insulation

Rafter area 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.

Insulating material

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

costs for possibly additionally necessary work

Sparrow doubling

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 sub-rafter insulation

Another possibility for additional insulation is the application of a sub-rafter insulation in addition to the inter-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 for additional under-rafter insulation

In our example, additional costs of approx. 10 - 20 EUR per m² - ie approx. 1,800 - 3,600 EUR in total should be assumed if a plasterboard covering is omitted. 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 rafters in the roof area
  • sufficient interior height of the rafters (no need for a double insulation)
  • already good insulating roofing

higher buoyancy factors

  • higher rafter spacing
  • uneven rafter spacing
  • geometrically complicated roof trusses
  • low interior height of the rafters (additional doubling required)

savings through self-construction or own contribution

The installation of intermediate rafter insulation and vapor barrier is a classical work for the DIY. However, you 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 cladding.

Saving options for intermediate rafter insulation

When you do the 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.

How to save when attaching the vapor barrier

If you are a little skilful and work well, you can also install 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 the interior trim yourself

If you also make the interior trim 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 in 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.


A large number of subsidies are 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 & TricksAlways ask a specialist to 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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