Snow and Metal Panel Roofs: Part 2


In part I of this blog, we discussed what to consider when deciding the roof material and roof slope to build with in snowy conditions. If you have decided to design a roof with metal panels, it is important to use the correct panel seams, evaluate the roof layout and consider long-term weatherproofing, and ensure your roof design fits the needs and function of the building.

Metal Building in Snowy South Dakota

Weathertight Panel Seams

For metal panel roofs less than 3:12 (i.e., low-slope roofs), the panel seams should be watertight. A watertight seam resists water intrusion, so snow on a roof should not become a leakage issue. For metal panel roofs with slope greater than 3:12, the steeper slope means liquid water (e.g., rain) drains very quickly off the roof. Because of this, many seams used for steep-slope metal panels are not watertight. Non-watertight seams can be problematic where snow stays on a roof. Architects should consider using watertight seams (e.g., double lock) and highly water-resistant underlayments in snow areas for all roof slopes.

Roof Layout

A designer should also consider the layout of the roof. Valleys collect snow. Valleys in which one roof area is significantly larger than the other (e.g., a dormer extending from a large roof area) are vulnerable to unbalanced sliding snow. A large snow slide can move across the valley and literally tear open the standing seams and displace panels.

Drifting snow can occur behind HVAC units, at perimeter walls and behind rooftop solar thermal and PV panels. Where a roof transitions from a lower low-slope roof area to an upper steep-slope roof area, snow will collect. Consider the potential snow load and entrapped moisture at these locations; the transition detail becomes critical to long-term weatherproofing.  And, depending on the orientation (e.g., north facing), areas with drifted snow may not see much sunlight, so snow is more likely to stay on the roof for a longer time.

Building Function

As the roof designer, design the building and site to account for the roof’s function. Many designers turn to snow retention devices to keep snow on roofs, especially above pedestrian areas, such as entrances and outdoor seating areas, or adjacent buildings.   Some of these devices rely on adhesive attachment to the panel, which means they rely on the adhesion of the paint to the metal. But physical attachment—e.g., snow fences clamped to the standing seams—is always a more confident, long-term approach than adhesive attachment when it comes to resisting shear/sliding loads. Using.multiple rows of snow fences, sometimes double in height, may be needed in areas that get large and prolonged amounts of snow (e.g., ski resorts), or where the eave to valley length is long, or where the slope is very steep.  Each increases the shear loads.

Designing a Snow Retention System

Snow retention systems need to be engineered, not guesstimated! Use online models to assist with designing snow retention devices. Input your snow load, roof slope, panel width, roof length (measured horizontally), overall width of the roof area, and the manufacturer and panel type. These inputs are needed to adequately engineer a snow fence assembly.  And remember, the snow loads are transferred from the fence to the panel seams, then to the panel clips and to the deck/structure.  The entire load path needs to be designed to handle the snow load.  Here is one model:

For more tips on designing a snow retention system, read “The Art of Properly Specifying Snow Retention Systems.”

Designing a metal roof for snow is a mix of logic, experience and engineering. We can design roofs in snow because of our everyday observations of roofs with snow on them. Stay observant; design well.

Properly Specifying Snow Retention Systems for Metal Roofs

The recent arctic blasts that hit the northeast brought to mind many things: hot cocoa, the evils of shoveling snow, a nice fire, the longing for a warm beach and, of course, how to properly specify snow retention systems on standing seam roofs. I’m not alone here, right?

All jokes aside, when I was scratching my brain for a new blog post, the cold weather and blizzards reminded me how easy it is to specify snow retention devices improperly. It might appear rather elementary at first; you might think it is as simple as planning for snow retention around entrances and frequent walkways. If so, you, along with many others, are mistaken. Let’s review some not-so-obvious areas to consider while planning a snow retention system for a standing seam metal roof.


If a gutter is used that has a face high than the pan of the metal roof panels, the gutter must be protected from sliding ice and snow. Gutters are designed for one purpose – to channel the water to a downspout. If it is left unprotected it cannot resist sliding ice and snow.

Pipe penetrations

As ice and snow slides down a roof and encounters a pipe penetration, the force can cause the pipe to move down slope and damage the roof jack and the roof, or shear the pipe at the roof surface.

Upper roofs draining into lower roofs

The upper roof should have a snow retention system installed to prevent ice and snow from falling onto the roof below. Without snow retention, the sliding ice and snow can cause extensive damage to the roof membrane and to equipment on the lower roof.

Panel seams perpendicular to the main roof slope

Connector roofs or dormers are typical examples of this type of roof area. The main roof slope provides a surface for ice and snow to slide toward the eave. If it then encounters a roof surface that is perpendicular to this main slope, damage to the roof panels and trim on these roof areas can occur.

Valleys in high snow load areas

Valleys allow for snow to slide down a surface that is perpendicular to the panel seams. This offers the potential to bend panel seams down or shear them from the panel.

Aside from considering these areas while planning your snow retention system, also use clamps instead of screws to attach the system to the standing seams of the roof panels. Screws not only perforate roof panels but can also pin the roof and prevent it from floating as designed. Clamps, by comparison, have been tested and can be engineered for the specific roof to which they will be attached, allowing for the snow load, roof slope, panel run length and other details. These clamps do not penetrate the roof membrane, do not hinder roof expansion and are easily installed with a screw gun.

Final Recommendations

Lastly, I recommend having a registered, professional engineer design a retention system that meets the specified snow loads for the project. Without their expertise, there are possible repercussions. If the snow retention system cannot support the snow load, it can result in an entire system failure and major roof damage. This could potentially cause snow and ice to fall and hurt bystanders.

By keeping all of these in mind, along with proper installation and maintenance, a snow retention system will help your SSR survive winter blasts and protect pedestrians, too.

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