Glazing is the glass (or glass-substitute material) fitted in a frame, window or door. The term refers both to the material itself and to the process of fitting glass in a frame. The choice of glazing largely determines the insulation, light transmission and safety of a building.
Types of glazing
Single glazing
One layer of glass. Barely insulating (U-value around 5.8). Only found in old buildings or unheated spaces such as a shed or summer house.
Double glazing (low-E glass)
Two panes of glass with an air or gas layer between them. The standard for homes:
| Type | Composition | U-value | Application |
|---|---|---|---|
| Double glazing | 2 layers + air | ~2.8 | Outdated, being replaced |
| Low-E glass | 2 layers + noble gas | ~1.6 | Basic new builds |
| Low-E+ glass | 2 layers + noble gas + coating | ~1.3 | Standard new builds |
| Low-E++ glass | 2 layers + argon + low-emissivity coating | ~1.1 | Common in renovation and new builds |
Triple glazing
Three panes of glass with two gas layers. U-value around 0.6-0.8. Mainly for passive houses and highly energy-efficient construction.
Polycarbonate and acrylic
Plastic alternatives to glass:
- Polycarbonate — Impact-resistant, lightweight, widely used for canopies and conservatories
- Acrylic (Plexiglas) — Clearer than polycarbonate but less impact-resistant
Glazing for conservatories and garden buildings
When building a conservatory or garden building, the choice of glazing determines the use:
Conservatory
- Unheated conservatory: Single glazing or polycarbonate is sufficient. Cheaper and lighter.
- Heated conservatory: At least low-E++ glass required. Watch for condensation at the transition to the house.
- Roof glazing: Toughened or laminated safety glass is mandatory for glass roofs. Polycarbonate is a cheaper alternative.
Garden building
- As storage: Single glazing or polycarbonate is sufficient
- As workspace/office: Low-E++ glass for comfort and energy savings
- Roof: Always use safety glass for a rooflight
Safety glass
In certain locations, safety glass is mandatory (according to building regulations):
- Toughened glass — When broken, it shatters into small, blunt pieces. Used in shower enclosures and glass doors.
- Laminated glass (VSG) — Two panes of glass with a film between them. When broken, the glass sticks to the film. Mandatory for roof glazing and balustrades.
Fitting glazing yourself
When fitting glass in a wooden frame:
1. Clean the rebate — Remove old putty and paint residue
2. Place setting blocks — Plastic support blocks in the correct positions in the rebate
3. Place the glass — Set the glass on the blocks in the rebate
4. Fit glazing beads — Press the glazing beads in place with pins or small screws
5. Seal — Apply sealant between glass and frame (exterior side)
Related terms
- Frame
- Rebate dimension
- Clear opening dimension
- Balustrade
- Insulation value (R-value)