| Non-Thermally Broken Aluminum | Low to moderate insulation. The metal frame creates a direct heat path between the interior and exterior. | Approximately 45–65 mm | Commonly 50–80 mm, depending on the profile and hardware. | Strong, lightweight, corrosion-resistant when properly finished, and generally low-maintenance. | Unconditioned spaces, mild climates, garages, utility rooms, and projects where initial cost is the primary concern. | More likely to transfer heat and may develop interior condensation in cold conditions. It is usually less suitable for highly energy-efficient buildings. |
| Thermally Broken Aluminum | Moderate to high insulation. A polyamide thermal barrier separates the interior and exterior aluminum sections and reduces heat transfer. | Approximately 55–85 mm | Typically 55–90 mm, depending on the thermal barrier and reinforcement design. | Excellent structural strength and weather resistance with minimal routine maintenance. | Residential buildings, offices, apartments, and most heating or cooling climates. | Usually costs more than non-thermally broken aluminum, but offers better comfort and condensation control. Look for verified whole-window U-factor data. |
| High-Performance Thermally Broken Aluminum | High insulation when combined with wide thermal barriers, insulated glazing, warm-edge spacers, and effective seals. | Approximately 70–100 mm | Often 65–100 mm, because deeper profiles are used for larger barriers and thicker glazing. | Very durable and suitable for demanding weather exposure; finishes still require periodic cleaning and inspection. | Cold climates, hot climates, passive-house-oriented designs, high-rise façades, and large glazed openings. | Frame performance alone is not enough. Glazing, spacers, seals, installation quality, and drainage design strongly affect the final result. |
| Narrow-Sightline Casement Frame | Can range from moderate to high, depending on whether the narrow profile includes a thermal barrier. | Approximately 45–75 mm | Often 35–55 mm, providing a larger glass area and a slimmer appearance. | Aluminum provides good rigidity for slim profiles, but hardware and reinforcement must be selected for the sash size and weight. | Modern homes, daylight-focused rooms, architectural renovations, and designs requiring a minimal frame appearance. | Narrow profiles may have lower hardware capacity or glazing limits. Confirm maximum sash dimensions, glass weight, and air-tightness ratings. |
| Flush Casement Frame | Moderate to high when built with thermal breaks and insulated glazing. | Approximately 55–85 mm | Usually 55–90 mm, with the sash and frame aligned on the exterior or interior face. | Smooth exterior surfaces are easy to clean and can provide a contemporary appearance. | Contemporary façades, minimalist elevations, and projects where a level exterior appearance is preferred. | Check water drainage paths carefully because a flush appearance must still maintain reliable weather shedding and ventilation. |
| Rebated or Overlapping Casement Frame | Moderate to high, depending on the thermal break, seals, and glazing system. | Approximately 55–90 mm | Commonly 60–100 mm, generally wider than a narrow-sightline design. | Overlapping seals can improve weather resistance when correctly compressed and maintained. | Wind-exposed locations, replacement windows, and projects prioritizing robust weather sealing. | The larger frame profile may reduce the visible glass area. Seal compression and corner fabrication quality are important for long-term performance. |
| Aluminum Alloy Frame | Aluminum alloy is structurally efficient but naturally conductive; thermal performance depends primarily on the profile design and thermal barrier. | Varies by system; commonly 45–100 mm | Varies by system; commonly 35–100 mm | High strength-to-weight ratio, resistance to rot and insects, and low repainting requirements when factory-finished. | Most casement window applications, especially where slim profiles and long service life are desired. | Ask for the alloy designation, finish specification, coating thickness, and test documentation rather than judging quality by appearance alone. |
| Aluminum-Clad Wood Frame | Wood provides lower thermal conductivity than aluminum, while the exterior aluminum cladding improves weather protection. | Approximately 70–110 mm | Typically 65–110 mm | Exterior aluminum reduces exposure to weather; interior wood may require periodic cleaning, refinishing, or humidity control. | Traditional interiors, premium residential projects, and buildings that require a warm interior finish with a durable exterior. | Usually heavier and more expensive than an all-aluminum frame. Moisture management and high-quality junctions between wood and aluminum are essential. |
| Aluminum Frame with Double Glazing | Moderate to high when paired with a thermally broken frame, low-emissivity coating, argon fill, and warm-edge spacer. | Depends on the selected frame system | Depends on the selected frame system and glazing bead. | Good general-purpose durability with a lower weight than many triple-glazed units. | Moderate climates, renovations, and projects balancing energy performance, weight, and cost. | Performance varies widely. Compare the complete window U-factor and solar heat gain coefficient, not glass-center values alone. |
| Aluminum Frame with Triple Glazing | High potential insulation and improved interior surface temperature, especially with a thermally broken frame. | Often 70–100 mm or more | Often slightly wider because the frame must accommodate a deeper glazing unit. | Durable, but the heavier glass requires appropriately rated hinges, restrictors, and reinforcement. | Cold climates, noise-sensitive locations, and high-performance building envelopes. | Higher weight and cost can require stronger hardware and installation support. Solar gain and ventilation requirements should be reviewed. |
| Selection Checklist |
