What Is Snow Load

How Does Roof Pitch Affect Snow Load?

When it snows a lot, the shape of your roof really matters. This shape, known as the roof pitch, can make a big difference in how much snow piles up. 

If your roof is flatter, snow might build up and get very heavy. This can be bad for your house because it might cause damage. 

So, why do we care about the roof’s slope? It’s important for houses in places where it snows a lot. 

A good roof slope means your house can handle the snow without getting hurt. But, what’s the best slope for a roof in these snowy places?

In this article, we’re going to talk about how the slope of your roof helps keep your house safe when it snows. So without any further ado, Let’s get started.

Key Takeaways:

  1. Roof pitch significantly impacts snow load, with a 3:12 to 6:12 pitch ideal for efficient snow shedding.
  2. Snow load calculation considers snow depth, density, roof slope, and climate, essential for structural safety.
  3. Enhancing roof strength to increase snow load capacity involves structural improvements like additional beams.
  4. Reducing snow load is achievable through features like snow guards, proper insulation, and regular snow removal.

What Is Snow Load?

What Is Snow Load

Snow load is the weight of snow that a roof can hold. It’s measured in pounds per square foot. 

This matters because too much snow weight can damage a roof. It’s like having too many books on a shelf. 

If the shelf isn’t strong enough, it might break. The same goes for roofs with too much snow.

Understanding snow load is important, especially in places where it snows a lot. Different roofs can handle different amounts of snow. 

For example, a flat roof might hold less snow than a sloped one. The type of snow also changes the weight. Wet snow is heavier than light, fluffy snow.

Builders and homeowners need to know about snow load. This helps them make sure their roofs are strong enough. 

In some places, there are rules about how much snow load a roof must handle. This is to keep buildings safe and to prevent problems like leaks or collapses. 

What Is the Impact of Roof Pitch on the Snow Load?

So, how does the slope of your roof, known as the roof pitch, affect how much snow it can hold? The roof pitch is a big deal when it comes to dealing with snow. 

A roof that’s more slanted, or steeper, usually lets snow slide off easier. Think of it like a slide in a playground. 

When the slide is steeper, you go down faster. The same happens with snow on a roof.

On the other hand, a roof with a lower pitch, which means it’s flatter, tends to collect more snow. It’s like a flat table where things pile up and don’t slide off. 

This can be a problem because the snow gets heavy and puts a lot of pressure on the roof. Over time, this might cause damage or even make the roof cave in if it’s too much.

The right roof pitch can make a big difference in places with heavy snowfall. It’s not just about having a steep roof. It’s about finding the right balance. 

Too steep and it might be hard to build, too flat and it might hold too much snow. This balance is important to keep your house safe and to avoid problems with too much snow weight.

How Can I Measure the Roof Pitch?

How Can I Measure the Roof Pitch

Let’s break down the process of calculating roof pitch for both new construction and existing roofs:

For New Construction:

Firstly, when dealing with new constructions, begin by finding the overall height of your house. This is your starting point. 

Next, you’ll need to calculate the height of your attic. Do this by measuring the height of all floors excluding the attic and subtract this figure from the total height of the house. 

This gives you the estimated rise of the attic. 

The next step involves determining the span of the house, which is the distance across the width of your house, measured between the exterior walls. 

Once you have the span, divide it by two to find the rafter run. The final step in this process is to calculate the pitch of the roof. You do this by dividing the rise by the run.

For Existing Roofs:

When it comes to existing roofs, safety is very important. Ensure you use a ladder and fall protection equipment when accessing the roof. 

You will need a 12-inch or longer level and a tape measure or ruler. Place the level flat on the roof so that one end touches the roofing surface. 

Measure the vertical distance from the roof surface to the 12-inch mark on your level. This distance is the rise.

 For example, a 4-inch distance to the level means the roof rises 4 vertical inches for every 12-inch horizontal run, which gives you a pitch of 4/12. 

Using a combination square during this process can help in maintaining the level while making and recording the measurements.

Calculating Pitch from the Attic:

Calculating Pitch from the Attic

To calculate the roof pitch from inside the attic, bring a tape measure and a level with you. Place a 12-inch level so one end touches the sheathing or rafters, ensuring it is perfectly straight. 

If possible, you can clamp the level alongside a rafter for stability. From here, measure the vertical distance (up) from the 12-inch mark on the level to the roof. 

This measurement is your rise. The roof pitch is then determined by dividing this rise by the run.

What Contributes to Rooftop Snow Accumulation?

Now, let’s look at what causes snow to pile up on roofs. Several factors come into play, affecting how snow gathers and stays on your roof:

Roof Design

The shape and features of your roof are major factors. Flat roofs tend to gather more snow because there’s nowhere for the snow to slide off. 

Roofs with lots of valleys, like saw-tooth roofs, or those with obstructions like chimneys or skylights, can also trap snow in certain areas.

Wind Direction and Speed

Wind plays a big role in snow accumulation. It can blow snow into drifts, piling it up higher in some spots. 

This is especially true for roofs with barriers like parapets or walls, where snow can get trapped leading to snow load.

Roof Material

The type of material your roof is made of affects how snow behaves on it. Metal roofs, for instance, are more slippery, so snow slides off more easily. 

In contrast, rougher materials like asphalt shingles can hold onto snow for a longer period of time.

Surrounding Environment

The location of your house and nearby structures can also influence snow accumulation on your roof. 

For example, if your house is surrounded by taller buildings or trees, these can shield parts of your roof from direct snowfall or create areas where snow drifts.


What Is the Best Roof Pitch for Heavy Snow Load?

A pitch between 3:12 and 6:12 is often best for heavy snow load, allowing snow to slide off effectively while being architecturally practical.

How Do You Calculate Snow Load on a Pitched Roof?

Snow load is calculated by multiplying the snow’s depth by its density, then adjusting for the roof’s slope and local climate factors. You can do this by using a snow load calculator.

How Do I Increase the Snow Load on My Roof?

Increasing snow load capacity usually involves reinforcing the roof structure, possibly with additional beams or rafters, to enhance strength and support.

What Is the Basic Roof Snow Load Factor?

The basic roof snow load factor is a measure of the minimum snow load a roof should support, typically expressed in pounds per square foot (PSF).

How Can We Reduce Snow Load?

Reducing snow load can be achieved by installing features like snow guards, ensuring proper roof insulation, and regular snow removal to prevent accumulation.

How does Roof Pitch Affect Cost?

Roof pitch affects cost as steeper pitches require more materials and labor for construction and maintenance, potentially increasing overall expenses.


In summary, the design of your roof, especially its pitch, is crucial in managing snow load on your roof. 

A roof with the right pitch, usually between 3:12 and 6:12, helps snow slide off, reducing the risk of heavy accumulation and potential damage.

Calculating the snow load on your roof involves understanding the depth and density of the snow, along with your roof’s specific design features. 

Lastly, there are ways to manage and reduce snow load effectively. Installing snow guards, proper insulation, and timely snow removal can make a big difference. 

Remember, a well-designed and maintained roof is key to keeping your home safe during heavy snowfall.

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