A basement window wall

Basement windows are always tricky. In particular, in the case of a planned change in use, experience with one's own property may also show that it might make more sense to fill a basement window. In this guide we describe for you what you need to consider if you want to wall a basement window.

For older buildings basement windows have a very important task

For older buildings basement windows have an important job. They significantly regulate the humidity inside the cellar. Most basements of existing buildings until the 1970s are designed so that they are used as a deposit. At the same time moisture can rise in the cellar, which can then escape through the windows. This is the original principle, which was valid for centuries.

However, over time, especially at the end of the 20th century, there has been a change in user behavior. Living space is scarce and therefore basements are often used as living space, at least as a hobby or party room. In the case of these cellars, the light from the cellar is more prominent. So a cellar must show a certain dimensioning of windows, since otherwise it may not be used as (rented) living space.

Basement windows often fulfill these tasks

It may therefore be that a seemingly senseless set basement window to meet exactly these requirements. So, before you wall up a cellar window, you need to know the requirements for the cellar exactly:

  • possibly the basement window is needed for ventilation and moisture regulation
  • possibly the conditions must be met so that a basement apartment can be rented

Especially with older buildings so the lingering of a basement window can lead to fatal consequences and damage the fabric lasting. In contrast, the missing or too small window area for rented basement windows can quickly remedy the situation. So, especially in older houses, where the humid basement belongs to the venting concept of the house, you should consult an expert if necessary, if you are not sure.

Structural differences in basement windows

You must also take into account the construction of the cellar window. Depending on the circumstances on site, a basement window can be arranged differently:

  • Above-ground, free basement window
  • Basement window in front of a light shaft
  • Circumferential excavation around the house (for example concrete wall with 1 m distance to the house) with then conventional windows as basement window

The above-ground as well as the basement window with a circumferential light shaft or ditch can wall from the technical side like a conventional window. However, if the window leads to a light shaft, you must start further considerations.

Basement window with light shaft

This raises the question of whether the light shaft should be preserved as such or not. If not, there are again two possibilities: either the light shaft is taken out and then filled or the light shaft is filled. But then it should be remembered that, depending on the individual situation in extreme weather situations (downpours, heavy rainfall, rapid snowmelt), water can be forced into the light shaft from below. So it can be quite useful to completely disassemble a light well and then fill it.

The insulation of the outer wall

Another important aspect when filling the light shaft is the façade or basement wall insulation. In any case, a corresponding perimeter insulation must be installed here. But that can be different. First of all suitable materials should be used for walling the basement window. Optimal are the same building materials as they were used for the rest of the basement foundation.

Materials and insulation options in the bricked basement window

In general, concrete, concrete blocks, bricks are suitable. Less suitable are absorbent and strongly absorbent stones such as gas concrete (aerated concrete). Now it is usually plastered from the outside and then applied a sealing layer. This can be a bitumen-like material, but also plastic. Then comes another seal, mostly studded to the outside and with water drainage. How the structure of the basement wall insulation ultimately fails, but depends heavily on the conditions (dry, often standing or even oppressive groundwater, etc.).

Tips & Tricks

In particular, if a modern and high-quality insulation of the basement foundations is still lacking on the building, it is worth considering connecting the bricking of the basement window with a refurbishment of the basement outer walls. In any case, please pay attention to the special features mentioned at the beginning of this article (venting, drainage or legal basis for renting).

Video Board: DIY How To Remove and Install A Basement Window