Roof insulation what is useful and cost efficient

Many still underestimate the effect of roof insulation, and therefore consider it unnecessary. Why the roof insulation is particularly effective, and what type of roof insulation in which cases makes sense, tells you in detail this post.

Effectiveness of the roof insulation

Warm air always rises. For this simple reason, more heat is lost over the roof of a house than over the other components.

A professional roof insulation also ensures airtightness in the roof space. Due to the no longer moving masses of air, no train can form, which conveys the heat even faster to the outside. However, this only applies to heated attic rooms!

Roof insulation what is useful and cost efficient: insulation

Insulation of the upper floor ceiling

According to the EnEV, only heated parts of the building need to be insulated. That is, in general would be sufficient for an unheated attic, which is used only as a storage room, an insulation of the top floor ceiling, which is then mandatory.

Problems with the unheated roof space

But even if the top floor ceiling reaches the required U-value of 0.24 W / (m²K), there are still numerous problems with an unheated and drafty roof space, if the floor slab is not properly insulated and insulated on a case-by-case basis.

Even more problematic, however, is the change in the climate in the attic, if only the floor ceiling is insulated. The floor slab acts like a floor heating in the uninsulated roof space. Due to the - albeit small - heat losses in the loft during the heating season it creates a higher temperature than outside.

The radiant heat of the ceiling slightly heats up other components as well:

  • roof
  • purlins
  • rafter
  • battens
  • tile

The upward flowing warm air brings with it a lot of additional moisture in the roof space. Normally this is not a problem for uninsulated roofs, because they dehydrate again due to the natural ventilation.

However, insulation on the top of the ceiling is often problematic if it is not carried out properly or if it is located on unsuitable floor coverings.

If possible, no roof insulation in unheated attics

The entire problem is massively tightened if the roof is additionally made airtight. In the case of unheated lofts, in fact, only a professionally executed insulation of the uppermost storey ceiling should take place.

The required values ​​for the primary energy demand of the building, which have already been reduced by 30 percent with the introduction of the EnEV, must then be achieved in other ways in the area of ​​the heated rooms.

On-roof insulation, under-roof insulation, intermediate-spar insulation?

Decisive for the type of roof insulation here are effectiveness and costs. With an intermediate roof insulation one can assume costs starting from approx. 30 EUR per m², with rooftop insulation the average costs amount to approximately 200 EUR per m².

But the roof insulation is much more effective. The under rafter insulation is both in terms of cost and effect in the midfield. It is therefore necessary to find a reasonable balance here.

The condition of the roof and the local conditions have a significant effect on the costs. Rooftop insulation usually only makes sense if you can re-cover the roof.

However, what has been said here applies only to the pitched roof - insulation on flat roofs can also be carried out cost-effectively as on-roof insulation, and become necessary for their effectiveness (required U-value according to EnEV 2014: 0.20 W / (m²K)).

Video Board: How does efficient flat roof insulation work? Concepts from a construction site with Neopor