Load Distribution
Windward Wall Pressure
The windward wall experiences positive pressure (pushing inward) as wind impacts the building face directly. The coefficient is typically +0.8 for low-rise buildings and varies with height and exposure category.
Coefficient
+0.8
Action Type
Pressure (Inward)
Angle Range
0° - 30° (vertical surface)
Primary Use
Wall cladding, Structural frame design
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Leeward Wall Suction
The leeward wall experiences negative pressure (suction, pulling outward) due to the wake region behind the building. This suction is relatively constant regardless of wind direction and building height.
Coefficient
-0.5
Action Type
Suction (Outward)
Angle Range
All angles (constant)
Primary Use
Wall anchorage, Cladding fasteners
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Side Wall Suction
Side walls experience significant suction due to flow acceleration around building corners. This is often the critical case for cladding design and corner detailing, especially within a distance of h/5 from edges.
Coefficient
-0.7
Action Type
Suction (Outward)
Angle Range
All angles (constant)
Primary Use
Corner cladding, Edge details
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Windward Roof (Low Slope)
For low-slope roofs (0° - 15°), the windward surface experiences strong suction due to flow separation at the leading edge. This is the most critical case for roof uplift design and requires proper anchorage.
Coefficient
-0.9
Action Type
Suction (Uplift)
Angle Range
0° - 15°
Primary Use
Roof covering, Purlin design
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Windward Roof (Mid Slope)
At intermediate slopes (around 30°), the windward roof transitions from suction to pressure as the flow reattaches. The coefficient becomes slightly positive, pushing down on the roof structure.
Coefficient
+0.2
Action Type
Pressure (Downward)
Angle Range
~30°
Primary Use
Rafter design, Roof structure
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Windward Roof (Steep Slope)
Steep roofs (45° and above) experience significant positive pressure on the windward side as wind impacts the surface almost perpendicularly. This is analogous to a vertical wall condition.
Coefficient
+0.7
Action Type
Pressure (Downward)
Angle Range
~45°
Primary Use
Steep roof structures, Church roofs
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Flat Roof (Edge Zone)
The edge and corner zones of flat roofs experience the highest suction values due to vortex formation. These localized high suction zones require special attention in fastener design and membrane anchorage.
Coefficient
-1.8
Action Type
Suction (Uplift)
Angle Range
0° (edge zone)
Primary Use
Perimeter details, Corner zones
Governing Formula
F = qₚ × Cpe × A
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Flat Roof Snow Load
Flat roofs and low-slope roofs (< 15°) retain the full balanced snow load with a shape coefficient of 0.8. This represents 80% of the ground snow load, accounting for wind blowing some snow off the roof.
Coefficient
μ₁ = 0.8
Action Type
Vertical Load (Downward)
Angle Range
0° - 15°
Primary Use
Flat roofs, Low-slope industrial
Governing Formula
s = μ₁ × Cₑ × Cₜ × sₖ
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Pitched Roof Snow Load
For pitched roofs between 30° and 60°, the snow load decreases linearly as slope increases. Above 60°, snow is assumed to slide off completely. The coefficient accounts for the reduced retention capacity of steeper surfaces.
Coefficient
μ₁ = 0.8 × (60°-α)/30°
Action Type
Vertical Load (Downward)
Angle Range
30° - 60°
Primary Use
Residential roofs, Gabled structures
Governing Formula
s = μ₁ × Cₑ × Cₜ × sₖ
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |
Load Distribution
Snow Drift (Multi-Span)
At valleys, parapets, and roof level changes, snow accumulates in drifts due to wind transport. The drift load can be 2-4 times the balanced load and must be considered for structural design of valleys and connections.
Coefficient
μ₂ = 2h₁/b + 0.8
Action Type
Vertical Load (Concentrated)
Angle Range
Variable (drift geometry)
Primary Use
Valley gutters, Roof steps
Governing Formula
s = μ₂ × Cₑ × Cₜ × sₖ
Wind Pressure Coefficients (Cpe)
ASCE 7 / EC1| Surface | Angle | Cpe | Action |
|---|---|---|---|
| Windward Wall | 0° - 30° | +0.8 | Pressure |
| Leeward Wall | All angles | -0.5 | Suction |
| Side Wall | All angles | -0.7 | Suction |
| Windward Roof | 0° - 15° | -0.9 | Suction |
| Windward Roof | 30° | +0.2 | Pressure |
| Windward Roof | 45° | +0.7 | Pressure |
| Leeward Roof | All angles | -0.5 | Suction |
| Flat Roof (Edge) | 0° | -1.8 | Suction |
Snow Shape Coefficients (μ)
Eurocode 1| Roof Type | Shape | μ | Condition |
|---|---|---|---|
| Flat / < 15° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 15° - 30° | Single-span | μ₁ = 0.8 | Balanced |
| Pitched 30° - 60° | Single-span | μ₁ = 0.8 × (60°-α)/30° | Balanced |
| Pitched > 60° | Single-span | μ₁ = 0 | Snow slides off |
| Pitched 15° - 40° | Asymmetric | μ₁ = 0.5 / μ₂ = 1.0 | Unbalanced |
| Pitched 25° - 50° | Drift on lower | μ₁ = 0.8 + 2h/b | Snow drift |
| Multi-span (valley) | Valley gutters | μ₂ = 2h₁/b + 0.8 | Accumulation |
| Curved / Barrel | Cylindrical | μ₁ varies with α | Function of angle |