Seal old window

Thermal insulation is more important than ever today. Some of the biggest weaknesses are explicitly the windows in older buildings. In this guide you will find out how to seal old windows and what to consider compared to modern window seals.

People have always tried to insulate the windows they need

People have always built window openings in buildings. They also try to insulate these windows as efficiently as possible for just as long. First with skins and leather, later with transparent natural stones, then with lead-framed glass. With industrialization, large glass surfaces were possible for the first time. In the 19th. and 20. In the 19th century, double glazing came into focus. Due to the large number of old and existing buildings, we now differentiate between the following window types:

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  • Simple glazing
  • Double glazing (two wings, even box windows)
  • Double glazing (insulating window with vacuum or gas filling between the slices)
  • Thermal insulation windows (gas-filled and specially coated glass)

Apparently leaking windows are part of a centuries-old wetting experience

In the future, still windows with special solar films. The windows have always been part of the house ventilation and dehumidification concept. Because first, an exchange of air must take place. In addition, moisture rises from the ground, the temperatures usually produce a pressure in the house.

The warm, air enriched air now expresses it formally out of the house. The typical vulnerabilities are the windows here. Especially between the lifes and the window frame. Ultimately, however, it was part of the ventilation concept for centuries.

Towards the end of the 20th. There were fundamental changes in the 20th century

In the 1990s, highly efficient thermal insulation windows came onto the market for the first time. Of course, everyone wanted to save energy and install new windows like this. However, the window installation had not yet adapted to the new windows. The windows themselves are now absolutely airtight, but the frames are fitted with gas-permeable PU foam. As a result, it pressed the moist air into the wall (between the reveal and window frame) and here the air cooled down.

The result: mold growth on an unprecedented scale

Cold air can no longer hold as much water, so the cooling air has to give off water. Sweat or condensation water occurs in the walls, i.e. in the building fabric. This is exactly where the problem lies with old existing buildings that are to be fitted with ultra-modern thermal insulation windows. So the prerequisites must first be created so that such thermal insulation windows can be installed:

  • Window and door assembly according to RAL
  • separate house ventilation (preferably)
  • Thermal insulation windows
  • Appropriate facade insulation (no thermal bridges between window and facade)

Sealing old windows using different techniques

In the case of renovation, an old or existing building can be modernized accordingly. However, this is not always the intention. The owners often want to keep the original old windows in buildings that are worth preserving historically and in listed buildings. However, these windows must be sealed differently.

Sealing in half-timbered houses

You have to seal old windows so that they are tighter on the inside than on the outside. Inside, there must be no air between the window frame and the reveal. Darning cord (hemp) is used in old buildings such as half-timbered houses. These are stuffed between the reveal and the frame. The outside is then plastered with clay or clay and grouted. The sealing joint thus remains a construction and maintenance joint.

Sealing windows in old stone buildings

With ordinary stone buildings you can also insert a sealing tape, followed by PU foam. The inside is then completely sealed with silicone or acrylic. It is sealed to the outside in such a way that the joint remains open to diffusion, i.e. can ventilate. However, with this type of waterproofing with windows that are otherwise completely airtight, you have to ventilate the house sufficiently elsewhere.

If you renovate airtight, the total effort is greater

Either integrate a separate ventilation system (then you can convert the typical cold roof into a warm roof) or you have to adapt the ventilation (ventilation) through the windows to the structural requirements. Otherwise, incorrect ventilation can lead to mold very quickly. Failure to air the room also leads to this, because there are colder areas somewhere in the house (corners, outer walls, etc.).), in which condensation then forms.

Tips & Tricks If you want to seal your old windows according to modern standards, you should also tackle the thermal insulation of the facade. In addition, ventilation must be guaranteed. Only in combination with efficient facade insulation and equally effective house ventilation does the sealing of old windows produce a significant insulating effect, which in this way protects the building fabric for decades.