Snow Guards: Metal Roofs, Sliding Snow and Placement

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A metal roof is very good at getting rid of snow. That is part of its appeal in Colorado, and it is also the reason so many homeowners end up shopping for snow guards for metal roofs after their first real winter. Snow that builds up on a smooth steel or aluminum panel often sits quietly for days, then lets go all at once when the sun warms the panel or the temperature climbs. The result can be a slab of snow and ice dropping off the eave onto an entry walk, a deck, a gutter, a parked car or a person. Snow guards are small devices or rail systems fastened to the roof that hold snow in place so it melts off gradually or falls in smaller pieces. This guide explains why metal roofs shed snow the way they do, what is at risk below the eaves, the main types of snow guard systems, how placement and fastening work without puncturing panels, how guards relate to roof snow load, ice dams and gutters, how to remove snow safely, and what installation tends to cost.

Part of our Structure & Exterior guide — start there for the full picture →

Why Metal Roofs Shed Snow in Sheets

Snow on a roof is held in place mostly by friction against the roofing surface and by the bond between the snow and whatever it is sitting on. Asphalt shingles have a gritty, granule-covered surface and lots of small edges that grip snow. A painted metal panel is smooth and continuous. Once a thin layer of meltwater forms between the snow and the panel, there is very little left holding the snowpack in place.

Several things create that meltwater layer. Sunlight warms dark panels even when the air is below freezing. Heat leaking from the house into the attic warms the roof deck from below. A sudden thaw, which is common along the Front Range when a sunny day follows a storm, can warm the entire roof quickly. When the bond breaks, the whole snowpack on a roof plane can slide as a single mass, sometimes with a layer of ice on its underside.

FEMA’s Snow Load Safety Guide (FEMA P-957) notes that unless a sloped roof has snow guards or cleats, a sliding snow condition can occur. It also explains that steeper slopes shed snow more effectively, that snow tends to slide once roof pitch exceeds its angle of repose (roughly a 30-degree slope, often described as 6:12 or 7:12), and that roofs with shallower slopes can still shed snow. The guide notes that slopes as low as 10 degrees have been observed to shed snow, and that smoother roofing materials are more slippery than abrasive ones.

Many people choose metal precisely because of its longevity and hail resistance; the metal roof cost guide covers panel types and pricing. The sliding behavior is simply a trade-off that comes with the material, and planning for it is part of a good metal roof installation.

What Is at Risk Below the Eaves

The danger of sliding snow depends almost entirely on what is underneath the roof edge. A metal roof that drains onto open lawn may not need snow guards at all. A roof that drains over a front door is a different story. Common trouble spots include:

• Entries and walkways. Doors located under an eave, rather than a gable end, are the most common concern. A slab of snow can fall just as someone steps out.
• Decks and patios. Sliding snow can crack deck boards, break railings and bury furniture. Repeated impact can also overload the deck framing.
• Lower roofs, porches and sunrooms. Snow sliding from an upper roof onto a lower one piles up deeper than the snow already there.
• Gutters and downspouts. A moving snowpack can bend gutters, pull hangers loose or tear a gutter off the fascia entirely.
• Vehicles and outbuildings. Cars parked along a driveway under the eave, or under a metal carport roof, can be dented or have windshields broken. The carport guide covers how those structures handle snow.
• Plumbing vents, flues and rooftop equipment. Snow sliding down a roof plane can shear off vent pipes, bend chimney caps and damage solar panel edges.

The FEMA guide points out that sliding snow landing on porch or sunroom roofs and entrance canopies beneath gabled residential roofs creates an unbalanced load, and that the dynamic force of the sliding snow can produce a significant impact on the lower roof framing.

Types of Snow Guards

Snow guards come in two broad families. Both are meant to break up the snowpack and hold it on the roof long enough to melt or fall in smaller amounts.

Pad-Style or Individual Snow Guards

Pad-style guards are small individual units, usually made of polycarbonate plastic, cast aluminum or stamped metal, installed in a staggered pattern across the roof. Each one grips a portion of the snowpack, and together they act like a field of anchors. They are relatively inexpensive, low-profile and less visible from the street. On exposed-fastener metal panels they are usually fastened through the panel or bonded with an adhesive approved by the guard manufacturer. On shingle and tile roofs, they are often installed under the roofing course and nailed to the deck.

Rail or Bar Systems

Rail systems, sometimes called snow fences or bar guards, run continuously across the roof in one or more horizontal lines. A rail system usually consists of metal brackets or clamps spaced along the roof, holding one or more aluminum bars or pipes. Because the rail spans the whole roof width, it creates a continuous barrier rather than a pattern of individual stops.

Rail systems are common on standing seam roofs and on larger or steeper roofs where heavy snowfall is expected. They are generally more expensive than pad-style guards but can hold more snow per linear foot when properly engineered.

Choosing Between Them

The right choice depends on roof type, slope, expected snow depth, what is below the eave and the look the owner prefers. For mountain homes with deep snowpacks, a rail system with multiple rows is often used. For a modest Front Range ranch house with one entry under an eave, a band of pad-style guards above the door may be enough.

Placement and Fastening Without Puncturing Panels

Where guards go on the roof matters as much as which type is used. The most common rule of thumb is to install the first row near the eave, typically above the exterior wall line, so the guards sit over a stable part of the structure and stop snow before it reaches the overhang. Longer roofs often need additional rows further up the slope so that no single row has to hold the entire snowpack above it.

Some general placement principles:

• Install guards across the full width of any roof plane that drains over a hazard, not just a short section above a door. Snow released at the edge of a short run can still drag adjacent snow off the roof.
• Space rows according to the manufacturer’s tables, which take slope, roof length and snow load into account.
• Place guards above dormers, valleys and lower roofs where sliding snow could concentrate.
• Protect vulnerable penetrations such as plumbing vents and flues with guards or small diverters installed just upslope.

Clamp-On Systems for Standing Seam

Standing seam metal roofs have raised seams where adjacent panels lock together. Because the fasteners on these roofs are hidden under the seams, many owners want to avoid making new holes through the panels. Clamp-on snow guard systems attach to the seams with set screws that grip the seam without piercing it. The rail or pad then mounts to the clamp. This approach preserves the roof’s weathertightness and generally keeps the panel manufacturer’s warranty intact, though owners should confirm compatibility with the panel profile.

Clamp-on hardware has to be matched to the seam shape and tightened to the torque the manufacturer specifies.

Exposed-Fastener Panels

Corrugated and ribbed metal panels with exposed screws do not have seams to clamp onto. Guards on these roofs are typically fastened through the panel into the purlins or deck with gasketed screws, or bonded with adhesive. Screws should go into solid framing, not just the thin panel, and every penetration needs a proper sealing washer. Adhesive-mounted guards should be installed in the temperature range the adhesive requires; many failures trace back to guards bonded in cold weather or onto dirty panels.

Snow Guards and Roof Snow Load

A question that comes up often is whether holding snow on the roof adds load. In one sense it does: snow that would have slid off stays on the roof until it melts. Roofs in Colorado are designed for local snow loads, and a sound roof built to code is meant to carry its design load whether or not the snow slides. Snow guards do not change the design load, but they do mean the roof regularly carries more of it.

That is one reason why the structure under the roof matters. The FEMA guide describes how the weight of one foot of fresh snow can range from about 3 pounds per square foot for light, dry snow to about 21 pounds per square foot for wet, heavy snow, and that one inch of ice weighs a little less than 5 pounds per square foot. The guide also stresses that unbalanced loads from drifting and sliding snow can be more of a concern than uniform loads. Snow guards, by keeping snow from dumping onto lower roofs and porches, can actually reduce one of those unbalanced load conditions.

The guards themselves also carry significant force, which gets transferred into the roof panels, the seams and the framing. A heavy, wet snowpack pushing against a rail can put substantial stress on clamps and fasteners. On older roofs, or roofs with sagging rafters, it is worth having the structure looked at before adding guards. The roof snow load guide explains design loads, warning signs and when to call a structural engineer.

Ice Dams and Gutters

Snow guards and ice dams are related but separate problems. An ice dam forms when heat escaping from the house melts snow on the upper roof, the meltwater runs down to the colder eave and refreezes, and a ridge of ice builds along the edge. On a metal roof, the snow that would normally slide off is now held back by guards, so whatever is happening with attic heat loss is more likely to show up as icicles and ice at the eave.

Snow guards do not cause ice dams, but they can make an existing heat-loss problem more visible. The underlying fix is usually air sealing and insulation in the attic. ENERGY STAR’s Attic Air Sealing Project page lists ice dams in winter among the symptoms that suggest a home may benefit from attic air sealing, and notes that air sealing combined with attic insulation can help alleviate the formation of ice dams. The ice dams guide covers causes and prevention in more detail.

Gutters are a related concern. On metal roofs without snow guards, sliding snow tends to tear gutters off. With guards in place, snow melts slowly and the gutters see more meltwater and more ice. Some owners use larger, stronger gutter hangers, and some skip gutters entirely on metal roofs and manage runoff at grade instead. Gutter guards can help keep debris out, but some styles can collect ice. The gutter guards guide compares the options, and the gutter repair guide covers bent sections, loose hangers and leaking seams after a hard winter.

Removing Snow Safely

Snow guards reduce the need to get snow off a roof, but there are still times when snow removal makes sense, such as when snow is extremely deep, when it is loading a lower roof unevenly, or when there are signs of structural distress. The safest approach is almost always to stay off the roof.

OSHA’s hazard alert on falls and other hazards to workers removing snow from rooftops is written for employers, but its lessons apply to homeowners too. The alert states that falls cause the most worker fatalities and injuries during rooftop snow removal, and that workers may fall off roof edges, through skylights and from ladders. It recommends using methods that do not involve going on the roof when possible, such as snow rakes or drag lines from the ground, and it lists other hazards including roof collapse, entrapment under falling snow and contact with power lines.

A few practical points for homeowners:

• Do not climb onto a snowy metal roof.
• Use a long-handled roof rake from the ground, working from the eave upward in small sections, and stand well clear of the fall zone.
• Watch overhead for power lines and service drops before raising a metal rake.
• Remember that snow guards are designed to stop snow, so raking above a guard row can leave a ridge of packed snow behind the guards.
• For deep snow on a large or steep roof, hire a contractor who has fall protection and insurance.

What a Home Inspector Looks For

During a pre-purchase inspection on a home with a metal roof, an inspector may note whether snow guards are present over entries, decks, lower roofs and driveways. Other observations can include bent or missing guards, loose clamps on standing seams, rust or sealant failure around exposed-fastener guards, damaged gutters below sliding areas, and dents or impact marks on lower roofs. An inspector will also look for icicle staining at the eaves, which can point to attic heat loss.

Buyers looking at mountain or foothills properties should pay particular attention to entry locations. A beautiful timber-frame home with its main door under a long metal eave may need a more serious snow retention system than a typical Front Range house. The structure and exterior hub covers what inspectors check on roofs, siding and drainage, and the guide to hiring a home inspector explains how to choose someone familiar with local conditions.

Costs

Snow guard costs vary widely by product type, roof size, roof pitch, number of rows and local labor rates, so any figures should be treated as rough. Individual pad-style guards are often priced at a few dollars to the low tens of dollars per piece, with dozens or hundreds needed for a typical roof plane. Rail systems on standing seam roofs are generally priced per linear foot, and the total for a single eave run can reach several hundred to a few thousand dollars once clamps, bars and labor are included.

Installing snow guards during a new metal roof installation is usually less expensive than adding them later, since the crew is already on the roof and can lay out rows before the panels are finished. Retrofit installations still make sense when a specific hazard, such as a front door under the eave, becomes obvious after the first winter.

References

• Snow Load Safety Guide (FEMA P-957) — Federal Emergency Management Agency
• Falls and Other Hazards to Workers Removing Snow from Rooftops and Other Elevated Surfaces — Occupational Safety and Health Administration
• Attic Air Sealing Project — ENERGY STAR

Buying a home with a metal roof and a front door under the eave? Reach out and we can connect you with an inspector who checks snow retention, gutters and roof condition before closing.