IGU & Thermal Performance
Insulating glass units, gas fills, Low-E coatings, U-value, SHGC, visible light transmittance, seal failure, and condensation for the Red Seal Glazier exam.
- Describe the construction and components of an insulating glass unit (IGU)
- Explain the purpose and benefits of argon and krypton gas fills
- Define Low-E glass and describe how metallic coatings reduce heat transfer
- Interpret U-value, SHGC, and visible light transmittance ratings
- Identify the causes and symptoms of IGU seal failure and window condensation
Leçon 1
Insulating Glass Units (IGU)
What Is an IGU?
An insulating glass unit (IGU) is an assembly of two or more glass panes separated by a sealed air space. The air space creates a thermal barrier that significantly reduces heat transfer compared to a single pane of glass. IGUs are the standard for energy-efficient windows and curtain walls in Canadian construction.
A typical IGU consists of:
- Two or more glass lites - can be any combination of annealed, tempered, laminated, or coated glass
- Spacer bar - aluminum, stainless steel, or warm-edge composite material that maintains the gap between panes
- Desiccant - moisture-absorbing material inside the spacer that prevents internal condensation
- Primary seal - polyisobutylene (PIB) applied between the spacer and glass for moisture resistance
- Secondary seal - silicone or polysulfide applied around the perimeter for structural integrity and additional moisture protection
Air Space Width
The typical air space in an IGU ranges from 6mm to 20mm, with 12mm to 16mm being optimal for thermal performance. Too narrow a space allows excessive conduction; too wide a space allows convection currents that reduce insulating value.
Double vs Triple Glazing
Double-glazed IGUs (two panes) are the minimum standard for most Canadian construction. Triple-glazed IGUs (three panes with two air spaces) provide superior thermal performance and are increasingly required in northern climates and high-performance buildings.
An IGU is two or more glass panes separated by a sealed air space. The assembly includes spacer bars with desiccant, a primary PIB seal, and a secondary structural seal. The air space provides the thermal insulation.