What is a pane of glass?
A pane is an individual sheet of glass in a window, a door or a façade opening. In Dutch the word for a pane is ruit, which also means a diamond or rhombus — a reminder of early glass production, when small diamond-shaped pieces were cut from round blown discs of crown glass because that divided a circle with the least waste.
Thickness and weight
Float glass is normally available in 3, 4, 5, 6, 8, 10 and 12 mm. A useful rule of thumb for weight: glass weighs about 2.5 kg per square metre per millimetre of thickness. A 4 mm pane of 1 × 1.5 m therefore weighs roughly 15 kg; a sealed unit of two 4 mm panes plus cavity is already over 30 kg. That single figure tells you whether you can lift it alone and whether the frame and hinges will carry it.
Single, double, triple
- Single glazing — U-value about 5.7 W/m²K. Cold, prone to condensation and poor acoustically.
- Low-E double glazing — coated and gas-filled, U-value around 1.1 W/m²K.
- Triple glazing — U-value roughly 0.6 to 0.8 W/m²K. Heavy; always check that the frame and hinges can take the weight.
The lower the U-value, the less heat escapes through the pane.
| Single glazing | U-value about 5.7 W/m²K. Cold, prone to condensation and poor acoustically. |
|---|---|
| Low-E double glazing | Coated and gas-filled, U-value around 1.1 W/m²K. |
| Triple glazing | U-value roughly 0.6 to 0.8 W/m²K. Heavy: always check that the frame and hinges can take the weight. |
Safety glass
Where people can fall or walk into glass, ordinary annealed float glass is not acceptable. There are two types:
- Laminated glass — two panes with an interlayer between them. If it breaks, the fragments stay bonded to the interlayer. This is the safe choice in doors, at eye level and for glazing down to floor level.
- Toughened glass — thermally strengthened; on breakage it disintegrates into small blunt granules. Very strong, but it offers no barrier once broken, because the whole pane goes at once.
National building regulations set out where in a building safety glass has to be used, in what thickness and to what classification.
Practical: measuring and replacing a pane
- Measure the rebate, not the old pane — the old one may have been ordered wrong in the first place.
- Allow 3 to 5 mm clearance per side. Glass must sit free in the rebate; a tight pane cracks at the first temperature swing.
- Set the pane on setting blocks, not straight onto the timber, so the weight lands on the right points and water can drain.
- Always use cut-resistant gloves and a second person for panes over about 1 m². Never carry a broken pane flat — always upright, on its narrow edge.
Related terms
- Window frame
- Glazing bar
- Stained glass
- Rhombic roof plane
- Insulating glass
Want to know more about building terms? Visit our knowledge base at fredsdiyplans.com.