Table of contents:

Window reveal: construction and insulation
Window reveal: construction and insulation
Anonim

Hardly anyone knows the word window reveal, even if we all see it every day. Because the window reveal is an important element in the installation of windows and a potential weak point for thermal insulation. Failure to insulate the window reveal can cause significant energy loss and even mold.

Table of contents Table of contents Window reveal: What is it anyway?

  • What is special about the window reveal?
  • Risk of thermal bridges if the reveal is incorrectly insulated
  • Install windows in the reveal: how it works
  • How can the window reveal be insulated?

Table of contents Table of contents Window reveal: What is it anyway?

  • What is special about the window reveal?
  • Risk of thermal bridges if the reveal is incorrectly insulated
  • Install windows in the reveal: how it works
  • How can the window reveal be insulated?

A window reveal - also a window reveal - is the vertical cut through the wall that is created through the window opening: if you want to install a window in a wall, you have to leave a corresponding window opening in the outer wall. Of course, walls always have a certain thickness, so that vertical walls of wall thickness are created in this opening on the right and left. The vertical wall surfaces facing the window are the window reveals. The upper horizontal part of the opening is called lintel, the lower parapet. The window itself divides the window reveal into a so-called inner reveal with the window sill and an outer reveal with the outer window sill. If the lower part of the outer reveal is part of the masonry, it is a sole bench.

The material for the window reveal corresponds to the respective wall materials, for example sandstone, sand-lime brick, brick, concrete or wood. The window reveal itself is usually plastered and painted on the outside, inward, i.e. in the room, often also papered.

Accordingly, there are soffits for doors. In the case of wall arches, however, this only refers to the inner surface of the curved piece that stands on the last stone of the vertical wall, the so-called fighter.

What is special about the window reveal?

The window reveal is sometimes called window connection, masonry connection, wall connection or simply component connection. These names already indicate the meaning of the window reveal: it is the seat of the window and the only direct connection point between the window frame - the colloquial window frame - and the wall, or the transition between the wall and the window. And thus a sensitive zone with material transitions - there the masonry meets a frame made of wood, plastic or aluminum.

Different materials always mean different expansion when exposed to heat - there is a lot going on in terms of building physics. Transition joints and other connecting elements between the window and window reveal must therefore be tough, but always remain flexible. And above all, everything has to keep tight - the reveal is a possible weak point and it does the hard work. After all, only the window separates the interior from the often inhospitable outdoor area with rain, wind, hail and snow. In winter, this can mean differences of 40 degrees Celsius and more over a few centimeters, plus there are year-round differences in humidity between outside and inside.

The requirements for tightness have increased even more since the end of the 1990s when air-tight windows were installed in the reveal. With this so-called window stop, the windows are mounted in such a way that the seal must be denser on the inside than on the outside - hardly any space for any stretching exercises on the window frame. The joints are the only flexible area in the window reveal and must be filled in carefully.

Fensterrahmen anbringen
Fensterrahmen anbringen

Depending on the function, the window reveal is simply referred to as a window connection, masonry connection, wall connection or component connection.

Photo: iStock / brizmaker

Risk of thermal bridges if the reveal is incorrectly insulated

Thermal bridges occur at transitions from well-insulated to poorly insulated. This makes an area colder and therefore an attraction for condensed water. Incorrect insulation also creates thermal bridges with window reveals. Moisture can form on the inside of the room, usually causing mold. If new windows are installed, not only must the damage be removed by dismantling the old frame, but the soffit must also be insulated accordingly. Otherwise, new windows are useless and in the worst case, they even favor mold.

Install windows in the reveal: how it works

You can mount windows and doors in the reveal in different ways, this is called a stop. The decisive factor is the type of reveal and the type of window:

  • With the so-called blunt stop, the reveal is completely smooth and you can basically mount the frame anywhere. The more or less central installation is common, so that the resulting forces are optimally transferred into the masonry. The central position is also the most energetically favorable.

    The blunt stop is inexpensive, but only allows so-called one-step joints. This means that only one joint to the outside and one joint to the inside is possible. The inner installation joint seals the window towards the inside, while the outer, as a so-called functional joint, is also a wind and rain joint. With the other types, the two-stage joint formation allows two joints with different tasks to be performed on the outside.

  • The reveal has a recess on the inside, you can only mount the frame on the inside from the projecting edge. With this construction, the frame itself is structurally protected against direct rain, or it protrudes a little into the insulation of the outer wall. An absolute plus in terms of energy.
  • An external stop is less common. With him you can only install the window frame from the outside. Old houses on the coast often still have a construction in which the wind pushes the window against the wall.

How to fasten the frame in the window reveal

Under no circumstances should the window “float freely” and be anchored in the window reveal with dowels. Dowels are of course still needed, but they are only used to fix and fasten the often heavy window in the wall. The weight of the window itself rests on special carrying blocks, which are placed under the corners and posts, so that they carry the weight onto the wall from the start. You can use blocks as spacers on the vertical sides. All blocks remain permanently in place and must therefore have absolutely firm contact with the wall and be immobile. They must not impair thermal insulation or tightness.

If the window is mounted in the middle of the reveal, long metal frame anchors are usually used. They are inserted through the frame into the masonry, where they spread apart by spreading them apart. If the window is mounted on the edge of the reveal, special anchors or claws are used, which are stuck in the masonry but do not exert any pressure from the inside.

The joints between the window frame and window reveal

Without joints between the wall and the window, it is not possible to compensate for the stretching exercises of the materials at different temperatures and humidity levels. The joint widths should of course not be arbitrary, they are crucial for the tightness. The permissible tolerance values ​​are regulated by the DIN 18202 standard. For wooden windows, the minimum dimension of the joint width is then one centimeter, for plastic and aluminum windows it should be one to two centimeters. The Energy Saving Ordinance of 2016 (EnEV 2016) stipulates that connection joints between building components and walls should be permanently impermeable to air. But there is no one-size-fits-all system. Because the connections between the component and the walls differ depending on the outer wall system and the type of window: sealing tapes, thermal tape, joint sealing tapes or, of course, sprayable sealants such as acrylic or silicone can be used.

However, the connection joints must generally prevent driving rain, wind and cold coming from outside, but at the same time allow steam to escape to the outside. Inner and outer seals must be coordinated. It is "denser inside than outside" so that the masonry and the components are optimally protected from moisture.

Versiegelte Fensterfuge
Versiegelte Fensterfuge

The joints between the wall and the window frame must be sealed, either with sealing tapes, thermal tape, joint sealing tapes or sprayable sealants such as acrylic or silicone.

Photo: iStock / OlyaSolodenko

How can the window reveal be insulated?

When insulating, you have to see a building as a whole: without appropriate insulation of the window reveal, external facade insulation does not do much - the narrow transition from inside to outside becomes a point of weakness and thermal bridges occur - with the moldy side effects mentioned above. And the heat finds every little weak point.

You can insulate the window reveal from the inside and / or outside. For this, you like to use reveal boards made of silicate, wood fibers, polystyrene, expanded clay or rock wool. Such reveal boards are significantly thinner than facade insulation boards, but have the same insulation effect. They have to be at least two centimeters thick and they should be attached seamlessly within the reveal area. The panels are glued to the clean and smooth surface and then mostly plastered. Important: The joint to the window frame must be sealed. This is done by plastering rails and overinsulation of the window frame.

If the house is insulated with a curtain-ventilated facade, you have to be particularly careful when insulating the window reveal. There must be no gap or joint between the facade insulation and the soffit insulation and the insulation material must go to the window frame.

Don't forget the window sills and roller shutter boxes above the window when insulating, there are also insulation solutions for this.

Reread windows later

If you replace old with new, better insulated windows, you can place the whole window differently in the reveal and, for example, move it forward. This is particularly useful if the facade would become thicker due to facade insulation and the window would otherwise lie in a thick wall like a loop hole. You do this in front of the facade insulation so that its insulation material immediately covers the transition from the wall to the window.

Thomas Hess

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