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The width of glass panel area that this mullion supports, typically half the spacing to each adjacent mullion.
For a mullion between two glass panels, the tributary width is usually half the panel width on each side (i.e. one full panel module width when panels are centered on mullions).
The height of glass panel area that this mullion supports.
For a vertical mullion carrying a full floor-to-floor panel, this is typically the full panel height.
About 25 kg/m² (5.1 lb/sq ft) for 10 mm glass. The glass makeup's surface density, including any laminated or insulated glass layers.
Use the total surface density of the actual glass makeup (monolithic, laminated, or IGU) — heavier makeups increase the mullion's tributary dead load.
Mullion tributary dead load
256 lb
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Curtain Wall Mullion Tributary Dead Load Calculator: 256 lb — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Mullion tributary dead load = tributary width × tributary height × glass weight per unit area, the standard tributary-area method for assigning distributed load to a supporting structural member
Inputs used
- Tributary Width
- 5 ft
- Tributary Height
- 10 ft
- Glass Weight per Area
- 5.12 lb/sq ft
What this calculation does not cover
- The answer is a mass — kilograms, or pounds once the imperial toggle is on — not a force. Convert it to a force before it enters any structural check, and do not paste it into the related mullion deflection calculator: that one asks for a horizontal wind line load per unit length, which is a different quantity from this vertical dead weight.
- Only the vertical dead weight of the glass is counted. Wind pressure, seismic and thermal movement, and any live or impact load sit outside this figure, and on most curtain wall mullions it is the wind bending case rather than the dead weight that sizes the section.
- The tributary-area split assumes equal panels centred on evenly spaced mullions and glazed on both sides. It does not hold at a building corner, at a jamb, or beside a door or opening where a mullion picks up glass on one side only, and it spreads the weight over an area when the glass actually lands on two setting blocks near the quarter points of the transom below.
- Nothing here checks where the weight goes once it reaches the mullion. The anchor, its bolts or embed, and the slab edge that receives it are a separate calculation, and whether the mullion is top-hung or bottom-bearing decides whether this dead load puts the section into tension or into compression, where buckling has to be checked as well.
- Tributary width is limited to 3 m (10 ft) and tributary height to 6 m (20 ft), capping the tributary area at 18 m² (194 sq ft). A mullion carrying glass through a two-storey atrium, or a module wider than 3 m, is outside those bounds — the field clamps the entry back to the limit and says so, and the load it then reports falls short of the real one in the same proportion.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Mullion tributary dead load = tributary width × tributary height × glass weight per unit area, the standard tributary-area method for assigning distributed load to a supporting structural member
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