How to Glaze a Window: Insulating, Upgrading, and Replacing Single Glazed Windows


What is single glazing? What advantages and disadvantages does it have? Where is it sensible to use single-glazed windows? How can single windows be improved? How are they isolated and exchanged? How to glaze a window?

With single glazing, surfaces are glazed with simple flat glass panes. Single-glazed windows offer little thermal and sound insulation. They are therefore not permitted in new buildings, but in old buildings there are ways of retaining single windows and improving the insulation.

Pros and cons of single glazed windows

The argument most powerful advantage of single-glazed windows is their low price. Another advantage is the variety of colors in which you can buy single glazing. Just think of decorative church windows or slug panes – they are usually made of simple glass. As a third advantage, one should mention the fact that single-glazed windows let a lot of light and heat into a room.

Typical uses of single glazing result from the advantages: They are used as basement window glazing as well as in garages, tool sheds, tool sheds or simple glass greenhouses in the garden, the preliminary stages of conservatories, so to speak. Simple glasses are also used for decorative purposes.

However, single glazing gives you little thermal insulation. This is their main disadvantage. Compared to modern thermal insulation glazing, which is standard in residential construction today, single-glazed windows let about five times as much heat through. The high heat transfer means high heating losses in winter, at the expense of the environment and your heating costs. And in the summer you quickly have the heat in the house.

But not only is a lack of thermal insulation a disadvantage of single glazing. They also offer little protection against noise from outside – in other words: hardly any sound insulation.

The third disadvantage of single-glazed windows is the risk of injury if the single pane breaks. Their fracture behavior no longer corresponds to today’s safety standards. Single- glazed windows are also insecure in terms of burglary protection: they offer almost no resistance to burglars.

Ways to improve thermal, acoustic and burglary protection of single-glazed windows

For situations where you don’t want to or can’t do without single-glazed windows, there are now ways of improving their disadvantageous properties – without having to change the glazing and/or the window right away.

Rubber seals

So you can improve the old wood putty seals of the single glazing with rubber grommets, which do not change the glass properties per se, but at least fix leaks, which are a common reason for draughts. Commercially available rubber seals last about three years and cost less than one euro per meter.

Window films

There are also special window films in specialist shops, which are traded as energy-saving films or cold protection films, among other things. According to their manufacturers, such films should insulate simple window glazing up to 65 percent better. Cold protection films are comparatively inexpensive and preserve the original look of the windows.

Front panes

A more costly way of improving heat and heating costs despite single glazing are so-called inner cover panes. Mount such elements, also known as energy-saving attachment panes, on the inside in front of the window. They bring more thermal insulation and soundproofing, but do not come close to the better insulation values ​​of modern thermal insulation glazing.

Doubling of the single glasses with additional panes

Inner attachment panes are movably mounted on existing window sashes. They can be equipped with the currently standard heat protection coatings. But: Such coatings reduce passive solar gains. You also have to bear in mind that historic window sashes have to carry the extra weight of about ten kilos per square meter with four-millimeter float glass.

A tubular seal is glued all the way round to each sash, which is intended to ensure that the additional pane is sealed tightly against the room. In order to prevent condensation in the space, holes must be drilled outwards in the casement frame to vent it.

In order to bring a historical window closer to current standards, an extra rubber seal is often placed in the folds of the window frame. This can be glued or placed in a groove milled into the frame and partially into the sash. But: The rubber seals pry up the windows on the side of the straps, so they can loosen over time.

In addition, the grooving weakens the cross-section of the frame wood of historical window constructions. Milling represents an irreversible intervention in the historical substance. Such an intervention contradicts the principles of monument protection and must not be carried out within the framework of monument preservation.

How to Glaze a Window

Before glazing, remember that you cannot glaze every window yourself. Modern thermal insulation glazing and insulating windows are double or triple glazed. However, there is only “air” between the glass panes in old double-glazed windows.

Modern insulating and heat-insulating windows either have a vacuum or are filled with an inert gas. In addition, it is often not just window glass, but vaporized or coated glass.

However, there are numerous windows that you can certainly glaze yourself:

  • basement window
  • Tool Shed Window
  • garage window
  • attic window 

You can either cut the glass yourself or have it cut to size by the glazier. In addition, you now have to differentiate between the material of the windows:

Glaze plastic windows

Plastic windows are blocked. This means that the glass pane rests on a block. The arrangement is usually as follows: a block at the bottom on the hinge side (where the window will be hung). The second then diagonally, i.e. on the outside (to the hinge) above.

On the side, blocks are placed in the same corners where the other two blocks are. All four blocks are arranged diagonally. The window only rests on the lower block. All other blocks are used for stabilization. Incidentally, you can also align a window here .

Glazing wooden and metal windows

For wooden windows you need special glazing pins or nails. These are hammered into the frame and fix the pane. With metal windows, special loops or eyelets are usually used, which are inserted into the holes provided and thus hold the glass.

Step-by-step instructions for glazing a window

Before starting, you need to prepare several equipment, such as hammer, screwdriver, putty knife, and glass cutter, if you want to cut the glass yourself.

1. Preparatory work

When you have placed the window you will see the bottom fold for the glazing putty. Here a correspondingly thick bead of window putty is inserted all around. Now you can carefully place the glass pane in the putty bed.

2. Fix the window pane

First the window glass is fixed in the frame. Now block the window or set the pins or the metal eyelets – depending on the type of window you have.

3. Cement the outside

Now the putty is used on the outside between the frame and the glass. If you have further questions about glazing putty, here you have access to an article on renewing window putty , for example .

4. Rework after glazing

Now the window putty has to harden on the surface. Now you can paint over it.

Tips and tricks: The timely painting of the window putty with a suitable paint (e.g. oil paint) is strongly recommended, as this slows down the occurring oxidation and the associated embrittlement and hardening of the linseed oil putty.


Thermal insulation is now one of the basic functions of modern windows in order to meet the energy requirements of the Building Energy Act. In addition to thermal insulation glazing, there are other types of window glass that offer you additional protection options. 

If you rather saving some money, you can try to glaze the windows yourself.But remember that certain windows cannot be glazed by yourself. However, you can do it for several types of windows by following the instruction provided above.

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