Window types and specifications guide
Understanding window operation types, frame materials, and performance ratings for construction.
Windows are specified in the architectural drawings and detailed in Division 08 50 00 (Windows) of the specifications. The window schedule on the drawings lists each window type with its size, operation, frame material, glazing, and hardware. Understanding window types and performance requirements is essential for verifying energy code compliance, coordinating rough openings with framing, and ensuring the facade performs as designed.
Window Operation Types
Fixed
Does not open - glass is permanently sealed in the frame
Advantages
Best air/water performance, largest sizes, lowest cost, best structural performance
Limitations
No ventilation, emergency egress not possible
Common Use
Storefronts, curtain walls, high-rises, display windows
Casement
Hinged on one side, swings outward using a crank operator
Advantages
Excellent air sealing when closed, full opening for ventilation, good for egress
Limitations
Cannot have exterior screens easily, wind loading when open
Common Use
Residential, low-rise commercial, operable windows in offices
Awning
Hinged at top, swings outward from bottom
Advantages
Can remain open during light rain, good air seal, stackable for ribbon windows
Limitations
Limited opening size, not suitable for egress, exterior projection
Common Use
Bathrooms, basements, clerestory windows, commercial buildings
Double-Hung
Two sashes slide vertically - both upper and lower sashes operable
Advantages
Traditional appearance, good ventilation control, easy to clean (tilt-in sashes)
Limitations
Lower air performance than casement, limited opening (50% max), complex hardware
Common Use
Traditional residential, historic renovations, institutional buildings
Single-Hung
Lower sash slides up, upper sash is fixed
Advantages
Lower cost than double-hung, simpler hardware, traditional look
Limitations
Only 50% operable area, lower ventilation than casement
Common Use
Residential, multi-family, budget-conscious commercial
Sliding (Horizontal)
One or more sashes slide horizontally on a track
Advantages
No exterior projection, simple operation, large opening sizes possible
Limitations
50% max opening, lower air performance, track maintenance
Common Use
Contemporary residential, patio doors, commercial service windows
Hopper
Hinged at bottom, tilts inward from top
Advantages
Good ventilation with rain protection (inverted awning), interior cleaning
Limitations
Inward projection, limited size, interior space impact
Common Use
Basements, commercial buildings, utility spaces
Projected (Project-Out)
Hinged at top or bottom, projects outward. Similar to awning but in commercial framing
Advantages
Ventilation with weather protection, large panel sizes in commercial framing
Limitations
Exterior projection, wind loading, limited opening angle
Common Use
Commercial curtain walls, ribbon windows, office buildings
Frame Materials
Aluminum
ModerateCommercial standard - storefronts, curtain walls, punched openings
Thermal Performance
High conductivity - requires thermal break for energy code compliance
Durability
Excellent corrosion resistance, no rot, minimal maintenance
Thermal break (polyamide strip) is essential to prevent condensation and meet U-factor requirements
Vinyl (PVC)
Low to moderateResidential standard, multi-family, budget commercial
Thermal Performance
Low conductivity - inherently thermally efficient
Durability
No painting, no rot, UV-resistant formulations available
Limited color options (typically white), structural limitations for large sizes
Wood
HighHigh-end residential, historic preservation, architectural projects
Thermal Performance
Excellent natural insulator
Durability
Requires painting/staining, susceptible to rot if not maintained
Often clad with aluminum or fiberglass on exterior for reduced maintenance
Fiberglass (Pultruded)
HighPremium commercial and residential, harsh environments
Thermal Performance
Low conductivity, dimensionally stable
Durability
Excellent - no rot, minimal expansion/contraction, paintable
Strength-to-weight ratio allows thinner profiles and larger spans than vinyl
Steel
Very highArchitectural projects, historic replications, fire-rated windows
Thermal Performance
Highest conductivity - requires significant thermal break
Durability
Extremely strong, thinnest sight lines, must be protected from corrosion
Fire-rated steel windows available for rated openings where glass is required
Performance Ratings
Window performance is measured by standardized ratings that must meet energy code requirements. These ratings are tested per NFRC (National Fenestration Rating Council) procedures and listed on the NFRC label.
U-Factor
BTU/hr·ft²·°FMeasures heat transfer through the entire window assembly. Lower is better - indicates better insulation.
Typical Values: 0.25–0.40 (commercial), 0.25–0.30 (high-performance)
Code Reference: IECC/ASHRAE 90.1 sets maximum U-factor by climate zone
SHGC
Dimensionless (0–1)Solar Heat Gain Coefficient - fraction of solar radiation admitted through the window. Lower blocks more solar heat.
Typical Values: 0.22–0.40 (commercial), varies by orientation
Code Reference: IECC/ASHRAE 90.1 sets maximum SHGC by climate zone and orientation
VT (Visible Transmittance)
Dimensionless (0–1)Fraction of visible light transmitted through glazing. Higher allows more daylight.
Typical Values: 0.40–0.70 depending on tint and coating
Code Reference: Not directly code-limited but affects daylighting calculations
Air Infiltration
CFM/ft² at 6.24 PSFRate of air leakage through the window assembly under pressure. Lower is better.
Typical Values: 0.06–0.30 CFM/ft²
Code Reference: ASHRAE 90.1 requires max 0.20 CFM/ft² for operable, 0.06 for fixed
Water Resistance
PSFPressure at which water penetrates the window assembly. Higher withstands more wind-driven rain.
Typical Values: 6–15 PSF (standard), 15+ PSF (high-performance)
Code Reference: AAMA/WDMA/CSA 101 sets minimum performance by product class
Structural (DP)
PSFDesign Pressure - wind load the window resists without failure. Based on building location and height.
Typical Values: 30–80 PSF
Code Reference: Must meet or exceed calculated wind pressure per ASCE 7
Glazing Types
Insulated Glass Unit (IGU)
Two or more glass panes separated by a sealed air or gas-filled space
Benefit: Primary thermal barrier - argon or krypton gas fill improves insulation
Low-E Coating
Microscopically thin metallic coating applied to glass surface to reduce emissivity
Benefit: Reflects infrared heat while allowing visible light - reduces U-factor and SHGC
Laminated Glass
Two glass layers bonded with PVB or SGP interlayer
Benefit: Safety glazing, sound attenuation, UV blocking, hurricane/blast resistance
Tempered Glass
Heat-treated glass that breaks into small granular pieces instead of sharp shards
Benefit: Required in hazardous locations per IBC Section 2406 (near doors, in showers, low sills)
Spandrel Glass
Opaque glass used in non-vision areas to conceal floor slabs, insulation, and structure
Benefit: Maintains uniform facade appearance while hiding construction behind the glass line
Ceramic Frit
Ceramic pattern (dots, lines, gradients) fired onto glass surface
Benefit: Bird-safe design, solar control, aesthetic patterns, partial opacity
Sources
AAMA/WDMA/CSA 101/I.S.2/A440 - NAFS Performance Standard
NFRC - National Fenestration Rating Council Standards
ASHRAE 90.1 - Energy Standard for Buildings
IECC - International Energy Conservation Code, 2024 Edition
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