Rules for a window sill

The masonry under a window also serves as fall protection. The minimum height of the window sill is specified in the building regulations of the federal states and depends on the building type, the type of use and the possible fall height. The parapet is in contrast to the railing of a closed construction.

Parapet, railing and grille

The window parapet is one of the structures in the construction sense, which includes railings and grids. Since window parapets have a greater depth than railings and grids, they are set slightly lower in the minimum heights required by the state building regulations.

Fall protection is mandatory if a drop of one meter is exceeded. Therefore, the rules for the fall protection of windows also apply on the ground floor.

Model building regulations and country regulations

In a prototype building code, the following window parapet heights for private residential buildings are specified as reference values:

  • Up to twelve feet fall height eighty centimeters
  • Over twelve feet fall height ninety inches

Railings and grids must have heights of fall of up to twelve meters and a height of 1.10 meters.

These values ​​were adopted by most state building authorities. Exceptions, deviations or additional regulations exist in the following states:

  • Baden-Wurttemberg
    The general height of the parapet and guardrail must be eighty centimeters if a minimum depth of twenty centimeters is given, otherwise ninety centimeters apply.
  • Bavaria
    The Free State examines the individual case and approves it individually. As a rule, the model building code is applied.
  • Brandenburg
    The minimum height for parapets up to twelve meters fall height is ninety centimeters, beyond 1.10 meters.
  • Hamburg
    The minimum depth of a window sill must be 15 centimeters.

measurement approach

The height of a window sill is measured from the top of the finished floor to the top of the windowsill. In most cases, the window frame width is ignored.

Compliance with the dimensions must also be observed when converting, enlarging or moving a window.

Energetically nonsensical window parapets

In the architecture of the 1950s to the 1970s, window sills were often tapered to partially sink ribbed radiators under the windows. Apart from the thermally questionable placement, the lower wall thicknesses led to losses in the insulating effect. In many cases, the design of the window sills, especially in multi-family houses, ensured that a good U-value of the window was counteracted by the insulation weakness of the balustrade.

An old window sill of this kind should be re-insulated in order to reduce the heat loss during heating. Styrofoam plates with an applied reflective layer can significantly improve the heat transfer coefficient. Another energy advantage can be obtained by extending the windowsill. The rising heating heat is redirected towards the interior and does not rise vertically at the window.

Tips & Tricks

Always plan your window sills with a few centimeters of tolerance, so that they do not fall below the building regulations minimum heights after the construction of the floor, for example through wood or laminate flooring.

Video Board: How I Make & Install Trim Around Windows After Exterior Styrofoam Insulation