What roof pitch is needed for snow load?
Roofs in snowy climates should have a slope of at least a 10-degree pitch minimum. A steeper angled roof sheds the snow more quickly. While the angle of the roof helps shed snow, adding too many angles to the roof for a more aesthetic effect could cause structural problems with snow shedding in the wintertime.
Anything over a 6:12 pitch tends to make massive amounts of snow slide off the roof without warning. Anything less than 1:12 pitch is a huge mistake in snow-prone climates. Standing seam metal roofs— which allow snow to slide more easily— might do better with a 2:12 or 3:12 pitch.
To figure out the load on your roof, take the depth of snow in feet and multiply it by the weight of a cubic foot of snow. If the snow weighs 10 pounds per cubic foot and there are 1.5 feet on the roof, each square foot of the roof is getting 15 pounds of pressure.
The short, simple answer is 2:12 has traditionally been considered the absolute minimum acceptable roof slope suitable for asphalt shingles. Asphalt shingles continue to be the most widely installed roof covering option in North America.
| Convert Roof Slope from Degrees to Standard Roof Pitch | |
|---|---|
| 13° | 2.770 in 12 |
| 14° | 2.991 in 12 |
| 15° | 3.215 in 12 |
| 16° | 3.441 in 12 |
Snow guards should be considered on slopes in excess of 30 degrees (7/12) in moderate to high snow load areas. On roof slopes approaching 45 degrees (12/12) snow is very likely to slide and snow guards should be considered in areas where it is necessary to control snow slides.
A steeper incline will allow the snow to fall more easily off of the roof. Therefore, experts recommend having a roof pitch of no less than 1:12 if you live in an area that is prone to heavy snow.
This downward imposed load on the home is also known as the snow load. The North Zone design live load equates to 40 pounds per square foot, the Middle Zone equates to 30 pounds per square foot, and the South Zone equates to 20 pounds per square foot.
As a rule of thumb, snow weighs approximately 20 pounds per cubic foot, or 1.25 pounds per inch of depth. Depending on moisture content, snow can weigh from 1 pound per cubic foot to over 21 pounds per cubic foot.
Any roofs up to 3:12 are generally considered “low slope.” In the residential arena, we see lower slope roofs as part of the home's architectural design. We also sometimes see low slope roofs on just certain areas of a home such as porches.
Can a metal roof have a 1/12 pitch?
Can You Put A Metal Roof On A Low Slope? Just about any type of metal roofing panel will work with a 3:12 roof pitch or greater. However, when the pitch drops to a 2:12 or even a 1:12, you will have to use the right metal roofing panel profile.
Roofers generally consider a low slope roof to be any roof at 3/12 or less, rising no more than three inches per foot of roof. A medium slope roof would be any roof between 6/12 and 9/12, and a high slope roof is any roof with a slope of 10/12 or greater.
The asphalt shingle manufactures recommend that you install asphalt shingles on a recommended minimum of 4 in 12 or greater however most manufactures will warrant their shingles down to a 2 in 12 pitch if the recommended installation method is used.
The 5/12 or 5 on 12 roof pitch are most common types of residential roof pitch which are a sloping surfaces with an angle of usually 22.62° degrees steepness of a roof with it's vertical rise of 5 inches over its 12″ or 1 foot horizontal distance or run in building construction.
The roof's pitch is the angle of the roof, usually presented as the inches of vertical “rise” over 12 inches of horizontal “run.” Generally anything above a 7/12 is considered a non-walkable roof and requires some extra equipment and usually some extra cost to the customer.
What roof pitch is 30 degrees? A 30° roof pitch is roughly the same as a 7/12 roof pitch.
Another way to express a 12/12 pitch is "12 and 12." In this pitch, the first twelve is your roof's rise and the second twelve is the roof's run. The roof's incline increases 12 feet for every 12 feet of horizontal measurement.
A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a “4 in 12” slope. If the rise is 6 inches for every 12 inches of run, then the roof slope is “6 in 12.” The slope can be expressed numerically as a ratio.
The slope that works best seems to be 5/12. This allows the snow to stay on while venting the roof system. They then have the option of putting dormers on the roof without damage to the valleys, penetrations, lower roofs, and property below due to sliding snow and ice.
At these slopes, snow creeps rather than slides and is easy to manage. On roof slopes between 4/12 and 6/12, rough textured roofing materials work best. They hold the snow in place and keep it from accumulating and then sliding off in large slabs that can be dangerous.
Will a 4/12 roof shed snow?
Snow can certainly slide off of a 4:12 roof. However, the larger factor is that when the sun comes out, radiant heat passes through the snow, is reflected outward, melts the snow from underneath and causes it to slide.
Most roofs can withstand 20 pounds per square foot of snow. 2. Calculate the weight of the snow on your roof. Ten inches of fresh snow equates to about five pounds per square foot, which means your roof likely can support four feet of fresh snow.
The trick is determining the weight per square foot of whatever combination of snow, ice, slush and water has piled onto your roof. If it's more than 30 pounds, the roof could collapse.
Unsurprisingly, wet snow is the heavy stuff. If it snows 5” of wet snow, it will weigh about 12.5 pounds. With this information, you're now likely wondering about the weight of snow load on your roof.
In general, roof snow loads are somewhere between 50-90% of the ground snow load, depending on the exposure and heat transfer.
If your main goal is to prevent ice dams, you should clear your roof after about every 6'' of snowfall. But if your main concern is a roof collapse, then raking your roof after every 12'' or more of snowfall should be adequate.
BONUS: Snow on your Roof Means Extra Insulation
An even covering of snow on the roof means that the insulation inside is working well. It also means that your home is receiving an extra layer of insulation against cold outside temperatures.
But did you know that heavy loads of snow can cause your roof to collapse? As snow builds up, the weight exerts pressure on your roof. When the weight of the snow exceeds the carrying capacity of the roof, it collapses.
Shingles can be installed on low-sloped roofs with a pitch of 3/12 inches. However, it will require additional layers under the shingles, such as a double layer of asphalt-saturated felt paper or a single layer of ice and water shield.
The costs of changing a roof pitch can depend upon numerous factors but will be anywhere from $15,000-$20,000 on average – large and complex roofs may cost more. Replacing the frame entirely – common in roof re-modelling – means switching out the ridges, walls and rafters too so it's a major project.
What's the minimum pitch on a metal roof?
The minimum slope for a metal roof with exposed fasteners and seams without sealant is 3:12, which means 3” of drop for every 12” of horizontal run. Roofing with exposed fasteners and lapped seams with sealant can go lower – ½:12.
Some might choose to skip using underlayment to save money. However, the metal roof underlayment acts as an added layer of protection. You can save money by using underlayment because it will help you avoid problems that would need to be fixed. The short answer is yes, your metal roof does need underlayment .
In many cases, a leaky metal roof might be attributed to insufficient roof slope. For most roofs with metal shingles, it's necessary to have four inches of rise for every foot of roof run, which equates to a slope of 4/12. If the slope is less than 3/12, you've likely found the source of the leak.
The traditional and most common material used for roof underlayment on a steep-slope metal roof is non-perforated, asphalt-impregnated felt underlayment. There are several types of felt underlayment including both organic reinforced and inorganic reinforced.
Steep Slope: 10/12 and above
Any pitch that's at least 10/12 (39.81 degrees) is considered steep slope. This includes 10 over 12, 11 over 12, 12 over 12, and pitch where the rise is greater than the run.
So a roof pitch of 10:12, as seen below, means for every 12 horizontal inches of roof, the roof rises 10 inches. This is a steep slope roof.
Lean-to Roof
A shed roof has a single sloping plane, making it the simplest of all roof frames to build. This style roof can be used on a freestanding outbuilding but is particularly well suited for sheds that are built up against another structure, such as a house, garage, stable, or barn.
Rubber roofs are a top choice for flat or low pitched roofing as it adheres to the roofing materials below it and, when installed correctly, provides a watertight seal to the elements. Choosing the best low slope roof materials often comes down to weighing the pros and cons based on your home and your needs.
The minimum roof pitch for shingles is a 2:12 pitch.
If your roof is less than 2 vertical units (inches or feet) up for every 12 horizontal units out, it's considered low slope. But why can't you put shingles on a low slope or flat roof? Shingles aren't meant to hold or have sitting water on them.
The slope that works best seems to be 5/12. This allows the snow to stay on while venting the roof system. They then have the option of putting dormers on the roof without damage to the valleys, penetrations, lower roofs, and property below due to sliding snow and ice.
Is a 4/12 pitch good for snow?
On roof slopes between 4/12 and 6/12, rough textured roofing materials work best. They hold the snow in place and keep it from accumulating and then sliding off in large slabs that can be dangerous.
Snow can certainly slide off of a 4:12 roof. However, the larger factor is that when the sun comes out, radiant heat passes through the snow, is reflected outward, melts the snow from underneath and causes it to slide.
A roof that rises 4 inches for every 1 foot or 12 inches of run is said to have a "4 in 12" slope. If the rise is 6 inches for every 12 inches of run, then the roof slope is "6 in 12." The slope can be expressed numerically as a ratio.