Curtain wall details
A guide to reviewing curtain wall systems on construction documents.
Curtain walls are non-structural exterior cladding systems that hang from the building structure like a "curtain." They resist wind loads and transfer their self-weight to the structure at each floor through anchors, but they do not carry any building loads. As one of the most complex and expensive building envelope systems, curtain wall detailing requires careful coordination across multiple disciplines.
Stick vs. unitized systems
Stick-Built System
Mullions and glass are assembled piece-by-piece on site. Vertical and horizontal mullions are attached to the structure, then glass and panels are installed into the frame.
Best for: Low-rise buildings (1 to 6 stories), complex geometries, small projects
- Lower upfront cost
- More flexible for irregular layouts
- Field-assembled joints, quality depends on installer skill
- Slower installation, weather-dependent
- More field sealant joints
Unitized System
Pre-assembled panels (typically one floor high, one module wide) are fabricated in a controlled factory environment and installed as complete units on site.
Best for: High-rise buildings (6+ stories), repetitive facades, fast-track schedules
- Factory quality control, better waterproofing
- Fast installation, crane-set one unit at a time
- Built-in movement accommodation at interlocking joints
- Higher fabrication cost, longer lead time
- Requires early design freeze, changes are expensive
Key detail locations to review
A complete curtain wall drawing package should include details at each of these critical locations. Missing details are a red flag, they often indicate unresolved coordination issues.
- Anchor connection to structure above
- Thermal break continuity
- Head receptor channel and gaskets
- Perimeter sealant and backer rod
- Spandrel panel attachment above
- Firesafing at slab edge
- Sill flashing and weep system
- Setting blocks for glass support
- Interior finish transition
- Condensation gutter or weep slots
- Pressure equalization chamber
- Integration with interior sill/millwork
- Mullion gasket and glazing pocket depth
- Structural silicone vs. captured glazing
- Thermal break alignment
- Adjacent wall transition and sealant joint
- Perimeter fire safing at columns
- Blind mullion at corners
- Vertical movement accommodation (live load deflection)
- Split mullion with sliding gasket or cover
- Firesafing and smoke seal at slab edge
- Structural anchor at each floor
- Thermal break continuity across joint
- Interior head/sill finish at each floor
- Corner mullion structural capacity
- Glass-to-glass butt joint vs. corner post
- Thermal performance at corner (thermal bridging risk)
- Sealant compatibility at glass-to-glass joint
- Corner anchor and structural backup
- Interior corner finish trim
- Top-of-wall cap flashing and counterflashing
- Air barrier and vapor retarder termination
- Metal coping attachment and expansion joints
- Transition from curtain wall to roofing membrane
- Lightning protection bonding
- Maintenance access provisions
Thermal performance considerations
Modern curtain wall systems include a polyamide (nylon) or polyurethane thermal break that separates the interior and exterior aluminum surfaces. Without this, the highly conductive aluminum frame becomes a major thermal bridge, causing condensation and energy loss.
Energy codes (ASHRAE 90.1, IECC) set maximum U-values for the overall fenestration assembly. Typical requirement: 0.36 to 0.42 BTU/hr·ft²·°F for commercial buildings in Climate Zones 4 to 6.
CRF (Condensation Resistance Factor) must be specified for cold climates. Target CRF of 60+ for most commercial applications. AAMA 1503 testing standard.
Non-vision areas (spandrel panels) require back-pan insulation to meet code U-values. Verify insulation R-value and vapor barrier location relative to dewpoint.
Multi-discipline coordination issues
Curtain wall installation touches nearly every trade. Identifying MEP-structural clashes early is critical, and proper firestopping at slab edges is one of the most commonly missed items.
Slab edge embeds must be cast before curtain wall installation. Verify embed locations, edge-of-slab tolerance (±1"), and deflection criteria (L/360 typical, L/240 for some systems).
Perimeter heating/cooling units (fan coils, radiant panels) must clear mullion anchors and firesafing. Verify clearance between slab edge and interior face of curtain wall.
Perimeter firesafing (safing insulation + smoke seal) is required at every floor slab. Sprinkler heads near curtain wall must maintain required clearance from spandrel glass.
Automated shade pockets, motorized vents, and facade lighting require power and control wiring routed to the curtain wall. Verify conduit locations in slab edge.
Interior sill heights, column covers, and ceiling-to-mullion transitions must be coordinated. Drywall returns to mullions need backing and thermal considerations.
Below-grade curtain wall transitions to waterproofing membrane. The air/water barrier must be continuous from below-grade wall through curtain wall perimeter sealant.
Sources
AAMA CW-DG-1, Aluminum Curtain Wall Design Guide Manual
ASTM E330, Standard Test Method for Structural Performance (Uniform Static Air Pressure)
ASTM E331, Standard Test Method for Water Penetration
ASHRAE 90.1, Energy Standard for Buildings Except Low-Rise Residential
Practitioner insight
“On a recent high-rise we caught two perimeter-fire-containment details that referenced the wrong UL system, the gap on the drawings was 1-1/2 inches but the cited UL system was only tested at 1 inch. That's a textbook AHJ correction notice, and we found it in the GC plan review before the architect knew. The fix at design time was a half-day of revisions. After permit submission it would have been a re-stamp and a four-week timeline hit.”
Conversations with VDC engineers and curtain wall consultants reviewing high-rise commercial curtain wall shop drawings between 2024 and 2026.
Frequently Asked Questions
What is the difference between a stick-built and a unitized curtain wall?
Which curtain wall details fail most often in the field?
What should a curtain wall shop drawing review verify?
How does curtain wall coordinate with structural and MEP design?
What codes apply to curtain wall design?
What is perimeter fire containment in a curtain wall assembly?
Manas Gandhi
Co-founder & CTO, HelonicManas is the co-founder and CTO of Helonic, where he leads engineering and AI research for construction drawing analysis. He works directly with structural, MEP, civil, and fire protection engineers to translate the way they review drawings into AI systems that flag the issues that actually matter in the field. Before Helonic, he built machine learning pipelines for technical document understanding and has spent the last several years interviewing licensed design engineers and discipline leads to ground product decisions in real practice rather than industry assumptions.
- AI for technical document understanding
- Cross-discipline coordination workflows
- Code compliance automation (IBC, NEC, NFPA, IPC, IMC, ASCE)
- Structural and MEP drawing review systems
Last reviewed by Manas Gandhi · May 2026
Keep exploring
Related guides on envelope detailing and facade coordination.