The Roof

This film illustrates all steps from stocktaking and evaluation of the existing roof construction including the roof windows and chimneys to the renovation of damaged roof elements and a professional thermal insulation of the roof.

The following explanations of the film are supplemented by architectural drawings and photos, which were created in the course of the research project to convert an old building into a low-energy house.

Energy Losses on the Roof

For inhabited or used rooms of an attic, the roof surface forms the largest part of the boundary surface and thus the largest part of the heat exchange surface.

The loss of energy in case of insufficient thermal insulation and leaky roof surfaces is very high, therefore energy-saving measures in this area are particularly efficient.

For existing inadequately insulated and sloped roofs, additional insulation can be installed between, under or above the rafters. Flat roofs are also suitable for additional or new thermal insulation. According to the GEG 2021, the minimum requirement for the heat transfer coefficient for roofs is U=0.24 W/m²K.

Inventory & Evaluation of the Roof Construction

As the upper limit of the building envelope, the roof is exposed like no other construction to the extreme stresses of rain, snow, wind, cold, and heat. Damage to roof structures, roof coverings, and their connections to skylights, chimneys, and gutters can be the result.

Damage to Wooden Structures

The examples in the pictures show damage and moisture in the roof structure. Moisture that penetrates through damaged roof coverings or is caused by the condensation of air humidity can cause decay.  Insects, fungi, or overstressing by loads can also cause damage to wooden structures.  

Damage to Roof Coverings

Before energy-saving measures are implemented, the existing roof structures must be examined.

If there is any damage to the roof coverings, these must first be repaired.

The picture example shows damage to the slate covering of a pitched roof.  

Thermal Insulation of the Roof Construction

If the roof covering is not renewed, it is recommended to choose between the rafter and under rafter insulation. 

In old buildings with a rafter height of less than 20 cm, additional under-rafter insulation should be installed. 

Different thermal insulation materials can be selected for this:  

  • Thermal insulation made of mineral wool or
    Heat insulation fillings made of cellulose, perlite, polystyrene balls, or crushed cork.

Attaching the Thermal Insulation

The thermal insulation must be laid without joints and the adjoining rafters must be fully bonded to avoid thermal bridges.

Defective areas must be filled with the same building materials.

Different Constructions of Flat Roofs

Non-ventilated Flat Roof

The substructure of the non-ventilated flat roof usually consists of reinforced concrete. 

This should already be laid out with a gradient for the planned drainage. 

Particular care should be taken to install the vapor barrier and the upper roof sealing to prevent the thermal insulation from getting damp. 

The thermal insulation must be sufficiently dimensioned according to the relevant guidelines.

Skylight Opening

Roof windows are essential components of architectural design. Their arrangement and structure determine the overall impression of the roof surface. 

The frames are often made from the wood of native forests, e.g. pine, spruce, or larch. Wood is a renewable raw material and can be processed easily. Due to its natural color and grain, wood has special aesthetic characteristics.   

An exterior cladding, e.g. made of anodized aluminum sheet, protects against rain, snow, sun, and wind.  

The heat transfer coefficients for roof windows required by the Energy Saving Ordinance can only be achieved with multi-pane insulating glazing.  

Installation of new roof windows

Windows that show greater damage must be removed and replaced with new ones. 

The replacement and new installation of roof windows require constructive measures in the area of the roof construction. 

When installing the roof window, leaks in the area of the vapor barrier and thermal bridges must be avoided.

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