Snow Load Design: Why Snow Matters in PEMB Engineering

Snow loading is one of the most important structural considerations in pre-engineered metal building (PEMB) design. In many parts of the country, snow can become the controlling force that determines frame sizing, roof system engineering, connection requirements, and even overall project cost.

To many building owners, snow may seem simple — snow falls on the roof, and the structure supports it. In reality, snow load engineering is far more complex.

Modern snow load design must account for:

Ground snow accumulation

Roof drift conditions

Uneven loading patterns

This guide covers how snow load design works in PEMB systems and why snow loading has to be engineered correctly for structural safety and building performance.

Snow load is the weight placed on a structure by accumulated snow and ice.

As snow collects on a roof system, it creates downward pressure on the structural framing.

Engineers must confirm the building can safely support these loads without:

Structural failure

Snow loads are commonly measured in pounds per square foot (psf).

Improper snow load design can create serious structural risks.

Potential problems may include:

Roof collapse

Excessive roof sagging

Snow loading becomes especially important in:

Northern climates

Large clear span buildings

Low-slope roof systems

Long-span industrial facilities

Even moderate snow events can create substantial structural loading.

One of the most misunderstood parts of snow engineering is the difference between ground snow load and roof snow load.

Ground snow load refers to the expected snow accumulation on the ground in a particular region.

This value is established by building codes and historical weather data.

Ground snow load varies significantly depending on location.

Roof snow load is the actual design load applied to the building roof after engineering adjustments are made.

Engineers account for factors such as:

Roof slope

Roof snow load is not always equal to ground snow load.

Many PEMB systems use relatively low-slope roof designs.

Low-slope roofs are more likely to retain snow accumulation compared to steep-slope roofs where snow may slide off more easily.

Because of this, flat and low-slope PEMB systems often require careful snow load analysis.

Snow drift is one of the most critical and dangerous snow-loading conditions in PEMB engineering.

Snow drift occurs when wind redistributes snow unevenly across the roof.

This commonly happens near:

Roof elevation changes

Parapets

Adjacent taller structures

Canopies

Instead of uniform loading, drift conditions create concentrated areas of very heavy snow accumulation.

These localized loads can become much higher than the general roof snow load.

Snow drift forces can dramatically increase structural demands.

Engineers may need to reinforce:

Rafters

Purlins

Connections

Drift zones near transitions

Improper drift analysis has contributed to many real-world roof failures across the industry.

Roof pitch directly affects how snow behaves on a building.

Steeper roofs may reduce snow accumulation by encouraging snow sliding.

However, sliding snow can also create new engineering concerns, including:

Drift buildup at lower roofs

Sliding snow hazards

Uneven load redistribution

Roof geometry must be carefully evaluated during snow load design.

Large clear span buildings are especially sensitive to snow loads.

Long spans create greater structural deflection potential and larger unsupported roof areas.

As clear spans increase:

Rafter sizes increase

Deflection control becomes more important

Snow drift effects become more critical

Structural reactions increase

This is one reason snow-loaded clear span buildings often require substantially heavier framing systems.

Building temperature can affect roof snow behavior.

Heated buildings may experience:

Snow melting

Uneven snow distribution

Cold storage buildings may behave differently than heated manufacturing facilities.

Thermal conditions are part of modern snow engineering analysis.

Modern PEMB snow design follows strict building code requirements.

Engineers must account for:

Local jurisdiction requirements

IBC code provisions

ASCE loading standards

Code requirements may vary significantly between locations.

The same building designed for one region may not meet code requirements in another area with heavier snow exposure.

Snow loading directly affects project pricing.

Higher snow requirements may increase:

Steel tonnage

Secondary framing size

Two identical buildings can have dramatically different costs depending on snow load requirements.

For example:

A warehouse in a low-snow southern region may require relatively light framing

The same warehouse in a northern snow region may require major structural upgrades

Snow loading affects the entire structural system, including:

Frames

Purlins

Connections

Columns

Foundations

Structural safety depends on engineered load paths and proper design criteria, not visual appearance alone.

Drift loading can create highly concentrated forces that are much greater than uniform roof loading.

Extreme snow events may occur only occasionally, but buildings must still be engineered to safely resist them.

Proper snow load design helps provide:

Structural reliability

Reduced maintenance issues

Improved occupant safety

Better roof performance

Snow engineering is not about overbuilding. It is about designing the structure to safely handle realistic environmental conditions over the life of the building.

Snow loading is one of the most important structural considerations in PEMB engineering.

Modern snow design involves more than estimating snowfall amounts. Engineers must evaluate:

Ground snow loads

Roof snow loads

Proper snow load engineering directly affects structural safety, long-term performance, and overall project cost.

Every project location has different environmental conditions, which is why accurate snow load analysis is essential when designing a pre-engineered metal building.