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