Glass is one of the most critical components of any aluminum window or door system. While aluminum frames provide structural strength and durability, the glass package determines thermal efficiency, occupant comfort, safety, acoustic performance, and overall system performance.
In North America, windows and doors are evaluated as complete systems under the North American Fenestration Standard (NAFS). This means that the frame, glazing, hardware, weather seals, and installation details all work together to achieve the required performance ratings.
This guide explains the most common glazing options used in modern aluminum fenestration systems and how they contribute to NAFS performance.
1. Annealed Glass
Annealed glass is the standard float glass produced during the manufacturing process. It has not been heat-treated and therefore offers the lowest mechanical strength among architectural glass products.
Advantages
- Economical
- Excellent optical clarity
- Easy to cut and fabricate
Limitations
- Breaks into large sharp fragments
- Low resistance to impact
- Poor thermal stress resistance
Because of these limitations, annealed glass is rarely used in locations where safety glazing is required by building codes.
2. Tempered Glass
Tempered (fully tempered) glass is produced by heating the glass to approximately 620°C and rapidly cooling it. This process creates compression stresses on the surface, making the glass approximately four to five times stronger than annealed glass.
Advantages
- High impact resistance
- Excellent thermal shock resistance
- Breaks into small relatively harmless fragments
- Meets safety glazing requirements
Typical Applications
- Doors
- Large fixed windows
- Floor-to-ceiling glazing
- Patio doors
- Areas close to walking surfaces
Tempered glass is commonly required by the Canadian Building Code in hazardous locations.
3. Heat-Strengthened Glass
Heat-strengthened glass undergoes a similar heating process as tempered glass but is cooled more slowly.
It is approximately twice as strong as annealed glass but does not qualify as safety glazing because it breaks into larger pieces.
Advantages
- Better resistance to thermal stress
- Reduced risk of spontaneous breakage
- Suitable for large curtain wall applications
4. Laminated Glass
Laminated glass consists of two or more glass panes permanently bonded together using one or more interlayers. Even when broken, the glass fragments remain attached to the interlayer, significantly improving safety and security.
Unlike tempered glass, laminated glass remains in place after impact, making it ideal for forced-entry resistance, overhead glazing, and hurricane-resistant applications.
Benefits
- Enhanced occupant safety
- Improved security
- Superior acoustic insulation
- Excellent UV protection
- Better storm resistance
- Reduced risk of falling glass
Types of Laminated Glass Interlayers
PVB (Polyvinyl Butyral)
PVB is the most widely used interlayer in architectural glazing.
Benefits include:
- Excellent optical clarity
- High UV protection (up to 99%)
- Improved acoustic performance
- Good impact resistance
- Cost-effective
Common configurations:
- 3+3 Laminated
- 4+4 Laminated
- 5+5 Laminated
- 6+6 Laminated
Multiple PVB layers may be used to achieve higher security ratings.
SGP (SentryGlas® Plus)
SGP is an ionoplast interlayer developed for demanding structural applications.
Compared to PVB, SGP offers:
- Approximately five times greater tear resistance
- Higher structural stiffness
- Better post-breakage performance
- Excellent resistance to moisture and edge exposure
- Superior hurricane impact performance
SGP is commonly specified for:
- High-rise buildings
- Structural glass walls
- Glass canopies
- Hurricane-resistant glazing
- Blast-resistant glazing
EVA (Ethylene Vinyl Acetate)
EVA interlayers are commonly used in decorative laminated glass.
Benefits include:
- Excellent adhesion
- High transparency
- Good moisture resistance
- Suitable for decorative inserts
- Often used for interior applications
5. Insulated Glass Units (IGUs)
Modern aluminum windows almost always use insulated glass units.
Double Glazing
Typical configuration:
6 mm Glass + 12 mm Air/Argon + 6 mm Glass
Advantages:
- Good thermal insulation
- Reduced condensation
- Lower heating costs
- Cost-effective
Triple Glazing
Typical configuration:
6 mm Glass + 12 mm Argon + 6 mm Glass + 12 mm Argon + 6 mm Glass
Advantages:
- Excellent thermal performance
- Lower U-Values
- Better indoor comfort
- Reduced exterior noise
- Preferred in cold Canadian climates
6. Low-E Glass
Low-Emissivity (Low-E) coatings are microscopically thin metallic layers applied to the glass surface.
These coatings reduce radiant heat transfer while allowing natural daylight to enter the building.
Benefits include:
- Lower U-Values
- Improved energy efficiency
- Better winter insulation
- Reduced summer solar heat gain
- Lower HVAC costs
- Improved occupant comfort
Most high-performance Canadian windows combine Low-E coatings with argon gas.
7. Argon and Krypton Gas Fill
The cavity between glass panes is commonly filled with inert gas.
Argon
- Most common
- Cost-effective
- Improves insulation by reducing heat transfer
Krypton
- Higher insulating value
- Ideal for narrow cavities
- Used in premium triple-glazed units
- More expensive than argon
Glass Performance Under NAFS
The North American Fenestration Standard (NAFS) evaluates the complete window or door system—not just the glass. However, the glazing package has a major influence on many performance categories.
Air Leakage
Proper glazing construction, spacer technology, sealants, and weatherstripping help reduce unwanted air infiltration.
Water Penetration Resistance
NAFS subjects window systems to wind-driven rain. Correct glazing methods, structural silicone, pressure plates, and drainage systems are essential to prevent water intrusion.
Structural Load Resistance
The thickness and type of glass determine how well a window resists positive and negative wind pressures.
Large commercial buildings often require thicker tempered or laminated glass to satisfy structural design pressures.
Forced Entry Resistance
Laminated glazing significantly improves resistance to forced entry because the interlayer holds broken glass together after impact.
Thermal Performance
Although thermal performance is primarily reported under the NFRC rating system in North America, the glazing package strongly influences overall window performance.
High-performance combinations typically include:
- Triple glazing
- Dual Low-E coatings
- Argon or krypton gas fill
- Warm-edge spacers
- Thermally broken aluminum frames
Acoustic Performance
Laminated glass with acoustic PVB interlayers can significantly reduce outside noise, making it ideal for homes near highways, airports, or urban environments.
Choosing the Right Glass Package
The ideal glazing solution depends on the building type, climate, energy goals, and project requirements.
For most residential and commercial projects in Canada, a high-performance insulated glass unit typically includes:
- Triple-glazed insulated glass
- Low-E coated surfaces
- Argon gas fill
- Warm-edge spacer system
- Tempered safety glass where required
- Laminated glass for enhanced security, acoustic performance, or impact resistance
Conclusion
Selecting the right glazing package is just as important as choosing the right aluminum framing system. A properly engineered combination of insulated glass, Low-E coatings, inert gas fills, tempered or laminated safety glass, and high-quality spacers contributes directly to energy efficiency, occupant comfort, structural durability, and long-term reliability.
When integrated into a thermally broken aluminum window or door and tested as a complete assembly, these glazing technologies help meet the demanding performance requirements of NAFS, ensuring excellent resistance to air infiltration, water penetration, structural wind loads, and the challenging climate conditions found across Canada.