Roof
roof pitch
Drempel
Flat roof
Upper floor slab
Solid ceiling
timber-beamed ceiling
Nail binder
Attic conversion
External wall
Façade
Partition joint in a house
cellar wall
Ground floor
cellar ceiling
Stairway to the cellar
Solid ceiling
Cap ceiling
Timber joist floor/cavity
Special components
In many window reveals in older houses, ‘mould stains’ can be seen. These are actually patches of mould. They always appear in places where, due to poor or lack of thermal insulation, the temperature falls below the so-called ‘dew point’. This is the surface where it is so cold in winter that water vapour in the air condenses (similar to the water droplets that form on a bottle taken out of the fridge). This moisture, combined with – ever-present – organic materials such as wallpaper, dust, etc., inevitably leads to mould stains.
If
- external walls are solid and uninsulated,
- external insulation has been installed incorrectly – i.e. the insulation has not been extended from the outside into the window reveal –
or if the wall is cavity brickwork,
black or grey patches may appear in the window reveal area. These patches are mould. This is not only an aesthetic problem, but also poses a health hazard.
The most effective measure is to insulate the window reveal from the outside. However, if it is not possible to insulate the window reveal, the only option is to treat the symptom: installing a reveal panel on the internal reveal.
Calcium silicate boards are the most commonly used soffit panels, as they have the following properties:
- capillary-active (i.e. any moisture that accumulates is absorbed throughout the board, distributed over a large area, stored and then released back into the interior)
- The board has a pH value of 10.5 and is therefore fungicidal. This means that mould growth on or within the board is virtually impossible. (Please note: the adhesive used must have the same properties! See below.)
- The board has an average thermal resistance of 0.062 W/m²K; depending on the board’s thickness, its surface temperature is therefore generally above the dew point.
The calcium silicate boards are coated over their entire surface on the adhesive side with the adhesive supplied with the system, using a fine-toothed trowel, and are bonded to the window reveal with a slight gap. An additional joint seal should be installed between the board and the window frame. As with any internal insulation, rear ventilation must be prevented in this case too. This also applies to small ‘air gaps’, to ensure that no moisture – and consequently no mould – can form on the masonry.
Calcium silicate boards are available as soffit boards from as little as 15 mm thick. If a thicker board is available, this should be used where possible, as the thicker the board, the greater its insulating effect and water-retention capacity.
All the benefits at a glance
Thermal insulation: As the panels are applied relatively thinly and do not have a high insulation value, the savings in heating energy are minimal or not measurable.
Advantages:
- Comfort is improved due to higher temperatures in the window reveal area
- Mould patches – and with them the health risks – disappear
- The window reveals become more visually appealing
- The work can also be carried out by the homeowner
Costs/Cost-effectiveness: As insulating the window reveals is less about thermal insulation – and thus saving on heating costs – and is primarily used to prevent mould, it serves first and foremost to protect the health of the occupants.
Funding: This insulation measure is not eligible for government funding.
Can I insulate it myself? Insulating the window reveal can also be done as a DIY project. Please follow the manufacturer’s installation guidelines! You should definitely stick to the recommended system and use the recommended adhesive. Tile adhesive, for example, is not suitable!
