Roof insulation - uncomplicated and effective


A loft insulation is a good alternative to a complete roof insulation, as long as the attic of the house is not used. It is fast and uncomplicated. Compared to other types of insulation, it is often very cost-effective, depending on the design.

About an uninsulated roof, up to 20 percent of the used heating energy is lost. In view of high and further rising energy prices, roof insulation can not be dispensed with. If the top floor is to be inhabited, a complete roof insulation is necessary to achieve a pleasant living climate there and in the rest of the building to avoid energy losses. For a permanently uninhabited attic roof insulation or the insulation of the top floor ceiling is an uncomplicated and cost-effective alternative. An extension of the attic and the installation of a complete roof insulation are then possible at any time.

Loft insulation - with high energy efficiency and relevant savings potential

Basically, a loft insulation has a high energy-saving potential, which is equivalent to a complete roof insulation (Aufsparrendämmung, Unter- or Zwischensparrendämmung). With a roof area of ​​100 m2 - calculated for the consumption of a heating oil system - an attic insulation can save up to 1,600 euros per year.

Table 1: Top floor insulation - Annual consumption and emission scenarios

(Calculation basis: 0.80 EUR per liter of heating oil)

insulation variantsOld building before 1978Thermal insulation according to EnEV 2009"Forward-looking" thermal insulation
Heating oil consumption (l / m2)212,41,2
Costs (EUR per m2)16,81,920,96
CO2 emissions (kg / m2)637,23,6
Heat transfer coefficient (W / (m2K)2,10,240,12

This somewhat older example calculation by the insulation manufacturer ISOVER shows quite impressively the potential of attic insulation. The "future-oriented" thermal insulation, which was not legally prescribed in the terminology of the company at the time, is largely identical to today's requirements of the Energy Saving Ordinance (EnEV) 2014.

Tips & Tricks

Roof insulation can significantly increase the energy efficiency of a building. With few exceptions, it is mandatory for buildings with uninhabited attic by the EnEV 2014.

The requirements for the thermal insulation of an uninhabited attic are prescribed by the EnEV 2014 binding. For newer buildings, the heat transfer coefficient (U-value) of the top floor ceiling must not exceed the limit of 0.24 W / (m2K). Exceptions apply to owner-occupied houses, which consist of a maximum of two apartments. These are not subject to the insulation obligation, if the current owner already lived in the house before February 01, 2002. The minimum thermal protection in such cases requires an insulating layer of about 5 cm. In the event of a change of ownership, an underfloor insulation or a complete roof insulation must be carried out within two years. All other buildings must be retrofitted by the end of 2015 with adequate thermal insulation of the attic / top floor or the entire roof. For new buildings, the EnEV requirements for the maximum permissible energy consumption of the building de facto make it mandatory from the outset to provide thermal insulation.

Insulation thickness and moisture diffusion

Structurally, a loft insulation can be made relatively easy. A foil is applied to the floor of the attic as a vapor barrier to protect the ceiling structure against moisture damage. If the top floor of a beam construction, it is checked whether the height of the bars for the thickness of the insulating layer is sufficient or an increase in the ceiling rafters by the installation of strips is necessary. The height of the insulating layer depends on the current EnEV specifications.

Table 2: Minimum insulation thickness of selected insulation materials according to EnEV 2014

insulationGlass and rock woolEPS / StyrofoamWood fiber insulation boardscellulosehemp
Minimum insulation thickness (cm)1414181616

Loft insulation - diffusion-open or diffusion-proof?

When it comes to the question of whether thermal insulation should be permeable to diffusion or diffusion-proof, in practice the ghosts are often different. In general, a loft insulation must be able to prevent the ingress of moisture into the top floor ceiling, but must not have a negative impact on the ventilation of the roof and ceiling construction. The introduction of a vapor barrier is generally recommended for beamed ceilings, otherwise an additional ventilation level is usually required between the underlay membrane and the insulating layer. For concrete floors, a vapor barrier may be omitted. Diffusion-open and capillary-active insulation materials ensure a good moisture balance in the roof truss even with an integrated vapor barrier.

Avoiding thermal bridges

Also important is a seamless connection of attic insulation and exterior wall insulation to avoid thermal bridges and thus energy losses and the ingress of moisture into the insulation layer and the ceiling structure.

Insulation of attic stairs

In rehabilitation projects, uninsulated floor stairs can prove to be a significant weak point of the attic insulation. It is recommended to replace such stairs from the outset with insulated stair structures. For walk-in attics it is also necessary to adapt the doors and the stairs to the new floor height.

Which forms of attic insulation are there?

A loft insulation can be done in several ways. The decisive factor is whether the attic is accessible, but is little to hardly committed or walkable. Depending on the resulting demands on the insulation layer, there are different possibilities for attic insulation:

Insulation on the top of the ceiling on a non-occupied attic

The easiest way for attic insulation is to apply the insulation layer to the top of the ceiling. For unpaved pointed floors no further construction is required for this. The insulation is laid or poured on the vapor barrier layer.

Insulation on the ceiling top in a walk-in attic

In a walk-in attic, however, a construction is required by which the insulating layer protects against mechanical stress and damage. Usually, the insulation is introduced for this purpose as bulk or Einblasdämmung between a construction of storage timbers and then covered by walk-in floor panels (for example, wood, particleboard or OSB boards, laminate). Again, a vapor barrier or barrier is usually required, which must be more vapor-tight than the flooring of the roof.

Walk-in attic insulation in multi-family houses

In many apartment blocks walk-in attics are divided into drying and storage rooms. In addition to the thermal insulation here is a footfall sound insulation necessary.

Insulation on the ceiling underside

For underfloor insulation of the top floor, new suspended ceilings - for example made of gypsum fiber or plasterboard - must be installed. The cavity between these and the ceiling construction is filled by the insulating layer, which may consist of nonwovens, felts, sheets or a blown insulation. The vapor barrier is installed below the insulating layer.

Insulation in the ceiling construction

For beamed ceilings that have sufficiently large cavities, it is possible to fill them with insulation - the optimal form of insulation here is a blow-in insulation. If the cavity does not allow the minimum thicknesses required by the EnEV, exceptions to these requirements are possible with this type of insulation, provided that the insulation material fills the entire construction space.

Which insulating materials are optimal for attic insulation?

Special requirements for the insulating material does not provide a loft insulation. For example, mineral wool, polystyrene-based foam boards - usually EPS / Styrofoam - or natural insulating materials such as cellulose or hemp are possible

Fleeces, felts, mats

Roof insulation of roofs that are not or rarely used usually consist of nonwovens, felt or mats. They are rolled out tightly on the ceiling construction as well as the vapor barrier film. A lamination or an additional, thinner fleece protects the insulating layer against damage.

insulation boards

For walkable floors either insulation boards or blow-ins are used. Rock wool, glass wool or EPS / Styrofoam insulation boards are by far the most widely used, but insulation solutions using natural materials - such as wood fiber or hemp insulation boards - are also possible. Especially for refurbishment they are often the better solution due to their physical properties, they are also mineral wool and plastics in terms of their sound and heat protection properties, at least in terms of tendency superior. Optimal is a double installation of the panels, which significantly reduces the risk of thermal bridges.

Which investments are necessary for a loft insulation?

Regardless of their design, a loft insulation is generally less expensive than the thermal insulation of the entire roof, since the floor area of ​​the attic is much smaller compared to this. The average cost per m2 is between 15 and 50 euros. By choosing high-priced insulation materials - such as wood fiber insulation panels - this can of course result in deviations.

Table 3: Average cost of attic insulation

executionCost per m2 (EUR)
Not committed floor ceiling15 – 25
cavity insulation15 – 25
Walkable floor slab incl. Floor construction40 – 50

Which form of attic insulation is recommended?

The insulation of a walkable floor slab is more expensive than a loft insulation due to the combination of thermal insulation and floor construction, which should not be committed. Nevertheless, builders should also plan for the future when deciding on one or the other type of insulation. If the attic is later used as a utility room, no retrofitting is required in terms of thermal insulation, if the insulation layer is accessible. In an expansion of the roof truss for residential purposes, although a subsequent roof insulation is required, but at least the insulation of the floor ceiling is completed. The higher investment in walk-in attic insulation is therefore worthwhile in the vast majority of cases, as building owners thus keep a wider range of possible uses open.

Can an attic insulation be funded by KfW?

There is a public interest in efficient thermal insulation because the energy transition can not be achieved without it. Even a loft insulation is basically eligible. Possible:

  • The KfW loan 152: Currently (2015) there is this loan with a maximum loan amount of 50,000 euros, an interest rate of 0.75% and 7.5% repayment subsidy.
  • The KfW grant 430: The funding amounts to 10% of the total investment, the upper limit is currently 5,000 euros.

If the roof insulation is part of a major refurbishment project, further funding is possible.

How is KfW funding applied for?

The application for funding must be made before the start of the construction work and will be submitted directly to KfW. The prerequisite for a KfW loan or construction subsidy is a professional energy consultancy and an expert opinion from the consultant, who usually also handles the application formalities.

Tips & Tricks

Roof insulation is an uncomplicated and cost-effective form of thermal insulation for an uninhabited attic. Even if the attic is not used at the time of construction, walk-in insulation is recommended to avoid later retrofitting.


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