Roof snow load: warning signs, safe snow removal, and what to do if you hear creaking¶

Snow looks light, but a roof can carry an enormous weight of it. After a heavy storm, or after a thaw and refreeze, tonnes of wet snow and ice can sit on a house, a barn, a garage, a shop or a flat commercial roof. Most roofs are built with a safety margin, but older roofs, flat roofs, roofs with damaged framing, and roofs that were never designed for local snow loads can fail without much warning.

This guide explains how to judge the load on your roof, which warning signs inside and outside a building mean danger, how to clear snow from the ground with a roof rake without climbing, how to deal with ice dams, and what to do if you hear creaking, popping or cracking. It adds detail to heavy snow, ice dams and roof collapse, which covers the basics of the hazard.

Do this now¶

1. If you hear loud creaking, popping or cracking from the ceiling or roof, or you see the ceiling sag, leave the building at once. Take everyone, including pets, and do not go back for belongings.
2. Call your local emergency number (911 in the United States and Canada, 112 across the European Union, 999 in the United Kingdom) once you are outside and at a safe distance from the building. Say that you fear a roof collapse. Find other countries on the emergency numbers page.
3. Stay out from under roof edges, awnings, porches and carports. Snow and ice can slide off a roof without warning, and a failing roof can drop its load outward.
4. Do not climb onto the roof, and do not use a ladder on icy ground. Falls and roof collapses are the main causes of death during snow removal.
5. Keep away from power lines, the electrical service entrance and gas meters when you work near the house, and report any damaged wires to the utility.
6. Once the danger is clear, arrange for a licensed contractor or structural engineer to inspect before you go back in.

How heavy is the snow on a roof¶

Snow weight depends on how much water it contains, not just how deep it is. A roof that is safe under 30 centimeters (1 foot) of dry powder may be in trouble under the same depth of soaked, packed snow or ice. Rain falling on snow makes things worse, because the snow absorbs the water and gets much heavier without changing in depth.

These are rough figures that vary with conditions. A common rule of thumb from emergency management agencies is that a roof may be at risk when it carries more than about 1.2 meters (4 feet) of fresh snow, or about 60 centimeters (2 feet) of old, packed snow. These numbers are only guides. A single heavy storm after earlier snow, rain on top of snow, drifts against a wall, and a roof with existing damage can all lead to collapse well below those depths.

Why design loads vary¶

Building codes set a design snow load for each location, based on past records. Your roof was designed for that load, plus a margin, if it was built to code and is in good condition. Older buildings, additions, DIY modifications, and buildings with rotted, cut, or termite damaged beams may not meet it. Roofs in places that rarely see snow were not designed for it at all, so an unusual storm can cause damage in a region that is unprepared.

Which roofs are most at risk¶

• Flat and low slope roofs. Snow cannot slide off, so it accumulates and can pond when it melts. Many collapses involve flat roofs on garages, commercial buildings, warehouses and barns.
• Large span roofs with few supports, such as barns, gyms, big box stores, and agricultural sheds.
• Roofs with drifting. Wind piles snow against parapets, taller walls, chimneys, dormers and where a lower roof sits next to a higher one. Drifts can be several times deeper than the snow on the rest of the roof.
• Older or poorly maintained buildings with rot, sagging, rusted fasteners or past water damage.
• Roofs with added loads, such as solar panels, rooftop equipment, extra layers of shingles or heavy roofing materials.
• Lightweight roofs of metal buildings, carports, pole barns and greenhouses. These can fail quickly under ice and wet snow.
• Pool and patio covers, fabric structures and tents, which have little reserve capacity.
• Roofs with blocked drains, scuppers or gutters, where water cannot drain away, and where melt refreezes. See flat roof scupper and internal roof drain clog.

Steeply pitched roofs shed snow more easily, but they are not immune, especially if snow sticks or ice forms, and the sliding snow can injure people below.

Warning signs of roof overload¶

Roofs usually give signs before they fail. Learn these signs and check for them after heavy snow, after rain on snow, and whenever a thaw is followed by a freeze.

Inside the building¶

• Creaking, popping, groaning or cracking sounds from the roof, ceiling or walls, especially if the sounds are new or loud
• A sagging or bowing ceiling, or visible deflection of ceiling tiles or roof joists
• New cracks in drywall or plaster, particularly around door and window frames or along the corners of ceilings
• Doors and windows that suddenly stick, jam, or will not open and close normally
• Cracks or bulges in interior or exterior walls, or movement at the joints of walls and ceilings
• Water stains, drips or leaks from the ceiling, which may show that ice dams are forcing water under the roofing
• Sprinkler heads that have been pushed down out of their normal position or that are leaking
• Bent, bowed, split or cracked rafters, trusses, beams, purlins or posts, or support columns that are leaning
• Pipes, wires or ductwork that are bent or have shifted
• Light fixtures or fans that have moved or hang unevenly
• Shifting or rattling of metal framing, or popping of fasteners

Outside the building¶

• A visibly sagging roof line, or a roof plane that looks wavy or dished
• Snow depth much greater than the area around, especially drifts against walls
• Large icicles and thick ice along the eaves, which point to ice dams
• Cracked or leaning chimneys, vents or walls
• A gap opening between the roof and a wall, or between a porch or extension and the main building
• Walls that bulge or lean, or masonry with new cracks
• Metal roofing that has bent or buckled, or roof panels that have lifted at the seams
• Gutters pulled away from the house or bent

If you hear creaking, step by step¶

1. Get everyone out. Walk calmly, and use the nearest safe exit. Pick up children and pets on the way, and leave belongings behind.
2. Move away from the building. Stay at least as far from the walls as the height of the building, because walls can fall outward and roofs can throw snow and debris. A garage or shed can be treated the same way.
3. Call for help. Call your local emergency number and explain that you fear a roof collapse. Tell them if anyone is missing or trapped.
4. Turn off utilities only if you can do so safely. If you smell gas or see wires hanging, do not go in to turn them off. Call the utility from outside.
5. Take stock outside. Count everyone and check for injuries. Do not go back in to look for someone. Tell responders where you think they might be.
6. Wait for inspection. Do not go back inside until a building inspector, engineer or fire service says it is safe. If a collapse has started, assume that further collapse can happen.
7. Document damage from a safe distance with photographs, and call your insurer.

If part of the roof has collapsed¶

Do not enter to rescue people unless you can do so without entering an unstable area. Call your local emergency number and describe the location of anyone trapped, what you can hear, and what the structure looks like. Search and rescue teams use special equipment to shore up the space. If you hear someone tapping or calling from the rubble, call it out to responders. For dust and debris from a ceiling collapse, see ceiling drywall or plaster sudden pancake collapse.

Safe snow removal¶

Removing snow reduces the load on a roof, but it is also dangerous. The main risks are falls, slides, power lines, overexertion and cutting yourself. For most homes, the best approach is to remove snow from the ground, using a roof rake, and to hire a professional for anything more.

When to remove snow¶

Consider removal when snow has built up to the depths mentioned earlier, when you see any warning sign, when a thaw and refreeze or rain on snow is forecast, or when drifts form against walls. Remove snow before it freezes into a solid mass, because ice is far harder and more dangerous to clear. If you are unsure whether your roof is at risk, ask a roofer, a structural engineer or your local building department. Do not guess if there are warning signs.

Use a roof rake from the ground¶

A roof rake is a long handled tool, usually with a wide blade or a slide, that lets you pull snow off the lower part of a roof from the ground. It is best for single story roofs and for the first 1 to 2 meters (3 to 6 feet) of the roof edge. See the rules below.

1. Use an aluminum or fiberglass pole only if you are sure there are no power lines near the roof. Aluminum conducts electricity. A fiberglass or plastic handle is better near wires.
2. Look up and around before you start. Find the service drop, the wires that connect your house to the power pole, and any other lines. Stay at least 3 meters (10 feet) away from lines, and farther if you can.
3. Stand away from the edge of the roof, outside the fall zone. Snow slides in sheets, and an unexpected slide can bury you or knock you down.
4. Pull snow down in layers, starting at the edge and working upward. Remove the upper layers first, leaving about 5 to 10 centimeters (2 to 4 inches) on the roof surface to avoid damaging the shingles or roofing.
5. Remove snow evenly from both sides of the roof. Removing snow from one side only can create an unbalanced load, which can be as dangerous as an overload.
6. Wear a hard hat, eye protection, gloves, and boots with good traction. Falling ice can injure the head and face.
7. Take breaks, drink water and stop if you feel tired or chilled. Overexertion is a risk. See shoveling snow safely for heart risks and technique.
8. Work with a partner who can watch the roof, the overhead lines and you.

Do not climb on the roof¶

Do not go onto a snowy or icy roof, even if you are experienced. A fall from roof height can kill or cause severe spinal and head injuries. Do not climb a ladder when the ground is icy or the ladder rests on snow. If someone must go on the roof, such as a professional, they should use proper fall protection, with a harness and anchored lines, and a ground crew.

Flat roofs, barns and commercial buildings¶

Do not send anyone onto a flat or low slope roof that may be overloaded. The weight of a person with a shovel on a stressed roof can trigger a collapse, and the person may fall through. Hire a professional snow removal contractor with experience in structural risk, with insurance and proper safety equipment. For barns, shops and large span buildings, call a structural engineer if you notice any warning sign. Keep livestock and people out of the building until it is cleared and checked.

Choosing someone to do the work¶

• Ask for proof of liability and workers' compensation insurance.
• Ask what equipment they use to protect the roof and the workers, such as harnesses, anchor points and plastic shovels.
• Be wary of door to door offers after a storm. Get at least two quotes if you can, and avoid paying everything in advance.
• Ask whether the crew will remove the snow evenly and leave a protective layer on the roof.

Ice dams¶

An ice dam is a ridge of ice that forms at the lower edge of a roof, blocking melted snow from draining. Water then backs up under shingles and leaks into the attic and walls. Ice dams happen when heat escapes from the house through the ceiling, melts snow on the upper roof, and the water refreezes at the cold eaves.

Signs of ice dams¶

• Thick ice along the edge of the roof, large icicles and ice in the gutters
• Water stains or drips on ceilings and along exterior walls, especially during a thaw
• Peeling paint, damp insulation or wet spots in the attic
• Ice behind the gutter that has pulled it away from the house

What to do in the short term¶

1. Remove snow from the roof edge using a roof rake from the ground, so that melt has somewhere to go. Remove the snow above the dam, which is the source of the water.
2. Make a channel through the ice dam with a calcium chloride ice melter packed in a long tube, such as a nylon stocking, and laid across the dam. Do not use rock salt, which can damage roofing, gutters and plants. Keep the ice melt away from pets and children.
3. Cool the attic by opening a vent, if it is safe to do so, and by turning down the thermostat.
4. Place buckets and towels where water enters, and protect belongings. See roof leak.
5. Call a professional if the dam is large, if water is entering the house, or if the roof is steep or icy. Professionals may use low pressure steam to melt the ice, which is safer for the roof than chopping.

What not to do¶

• Do not chip or hack at the ice with a hammer, axe, pick or crowbar. This damages shingles and can cause injury.
• Do not use a pressure washer or blowtorch.
• Do not climb on the roof to clear it.
• Do not pour hot water on the roof, since it can refreeze and make the dam bigger.
• Do not ignore leaks. Water in the ceiling can bring down drywall and insulation and cause mold.

Fix the cause¶

The lasting solution is to keep the roof deck cold. Seal air leaks around attic hatches, light fixtures, chimneys, plumbing vents and wiring. Add insulation to the attic floor to the depth recommended for your area. Make sure that soffit and ridge vents let air flow along the underside of the roof. Many agencies, such as the United States Department of Energy and Natural Resources Canada, publish advice on attic air sealing and insulation. A qualified contractor or energy auditor can help you plan the work before next winter.

After the snow: thaw, rain and refreeze¶

The weeks after a snowstorm can be as dangerous as the storm itself. A warm spell makes snow heavier as it soaks up water. Rain on snow can add the weight of the rain to the roof within hours. A rapid thaw can overload gutters, scuppers and drains, and a refreeze can block them again with ice.

Be most alert in these moments:

• When rain is forecast over deep snow
• When temperatures climb above freezing and then drop again
• When snow slides off a roof and piles on a lower roof or against a wall
• When wind has built large drifts

Keep drains and downspouts clear, and keep snow away from foundation vents, gas meters and chimneys. Make sure the area under eaves is clear, so that sliding snow does not trap or hit anyone.

Sheds, carports, greenhouses and pool covers¶

Lightweight structures fail first. If you have a metal carport, canopy, greenhouse or fabric shelter, clear snow from the outside with a soft broom or a push broom, working from the ground, before it builds up. Do not park vehicles, store equipment or shelter animals inside while heavy snow is on the roof. Remove snow from inflatable and air supported structures and pool covers, as manufacturers instruct. Never go inside a structure that is sagging or making noise. A cheap shed is not worth a life.

For pool and hot tub covers, see automatic pool cover or hot tub hard cover wind uplift or snow load collapse.

Decision flow¶

flowchart TD
    A["Heavy snow or ice on the roof"] --> B{"Creaking, popping, sagging<br/>or cracks right now?"}
    B -->|"Yes"| C["Leave the building now<br/>and call emergency number"]
    B -->|"No"| D{"Is the roof flat, old<br/>or carrying deep wet snow?"}
    D -->|"Yes"| E["Hire a pro or call an engineer"]
    D -->|"No"| F{"Single story and no<br/>power lines near the edge?"}
    F -->|"Yes"| G["Use a roof rake from the ground<br/>in layers on both sides"]
    F -->|"No"| H["Wait for a pro and stay off the roof"]
    G --> I{"Ice dam or water<br/>leaking inside?"}
    E --> I
    H --> I
    I -->|"Yes"| J["Clear snow above the dam<br/>and protect belongings"]
    I -->|"No"| K["Keep checking after rain<br/>or thaw and refreeze"]

Comparing snow removal options¶

Checklist for a heavy snow season¶

• I know the age and type of my roof and whether it is flat, low slope or steep.
• I have a roof rake with a non conducting handle, and I know where my power lines run.
• I have the number of a roofer or snow removal company and a structural engineer.
• I check the roof, ceilings, doors and windows after every heavy snow and every rain on snow.
• Attic insulation and air sealing have been checked, and vents are clear.
• Gutters, downspouts and drains are clear of leaves and debris before winter.
• Everyone in the household knows the warning signs and the exit plan.
• I have photos of the roof and my insurance details stored safely.

Monitoring a roof through a long winter¶

In a snowy region, a short routine catches problems early. After each significant snowfall, and after any rain or thaw, spend five minutes on the same checks. Look at the roof line from several sides, and compare it with a photo taken in summer. Walk through the rooms under the roof and look at the ceilings, the corners and the top of the doors. Open and close the interior and exterior doors to see whether they still move freely. Listen at night, when the house is quiet, for new sounds.

Write down the date and what you see. A small crack that grows over a few days is more worrying than a crack that stays the same. Measure it with a ruler, or mark the ends with a pencil and the date. If you see growth, call a professional rather than waiting for the next storm. Take photographs from the same positions each time so that you can see change.

What a professional inspection covers¶

A structural engineer or an experienced roofer will look at the framing in the attic and under the roof, the connections at the walls, the condition of the sheathing, signs of past leaks and rot, any earlier repairs, and the way snow drifts on your roof. They may recommend temporary shoring, such as posts under sagging beams, snow removal by a trained crew, or permanent reinforcement before the next winter. Ask for a written report. It helps with insurance and with any sale of the property.

Do not add temporary posts or braces yourself under a sagging ceiling. A wrongly placed support can concentrate the load and cause a sudden failure, and anyone working under a stressed ceiling is at risk.

Insurance and recovery¶

Photograph your roof, attic and ceilings before and after storms. Contact your insurer soon after damage occurs, and ask what the policy covers. Many policies cover collapse caused by the weight of snow, ice or sleet, but rules vary by country, region and policy, so read the terms. Keep receipts for emergency repairs, tarps, hotel stays and professional snow removal, since some policies reimburse reasonable costs to prevent further damage.

If water has entered the home, dry everything within 24 to 48 hours to limit mold, and remove wet insulation and drywall as advised. Do not use electrical items in wet areas, and have a licensed electrician check any wiring that has got wet. Do not reenter a damaged area until it has been cleared. For more on water damage, see roof leak.

Frequently asked questions¶

How much snow is too much for a roof?¶

There is no single number, because it depends on the roof design, age, and the water content of the snow. As a rough guide, emergency agencies treat about 1.2 meters (4 feet) of fresh snow or 60 centimeters (2 feet) of packed, old snow as a point to take action. Wet snow, rain on snow, drifts and flat roofs can cause problems at lower depths, so watch for warning signs rather than relying on depth alone.

What should I do if I hear my roof creaking or cracking?¶

Leave the building at once with everyone in your household, move well away from the walls, and call your local emergency number from outside. Do not go back in for belongings, and stay out until a building inspector, engineer or fire service says the structure is safe. Treat new creaking, a sagging ceiling or sticking doors as signs of overload.

Is it safe to shovel snow off my roof myself?¶

It is not safe for most people. Falls from roofs, slides of snow and contact with power lines cause deaths each winter, and the weight of a person can trigger a collapse on a stressed roof. Use a roof rake from the ground on single story roofs, and hire a trained professional for anything steep, flat, large or icy.

How do I get rid of an ice dam without damaging my roof?¶

Rake snow from the roof edge from the ground, then cut a channel with calcium chloride ice melt in a stocking laid across the dam. Do not chip the ice with tools, use rock salt or a flame, or climb onto the roof. For large dams or leaks, call a professional who uses low pressure steam, and fix the attic air leaks and insulation afterward.

Sources checked¶

This page was checked against the Federal Emergency Management Agency (United States) and Ready.gov guidance on winter storms and roof snow loads, the Federal Alliance for Safe Homes advice on snow and roofs, the National Weather Service (United States) winter safety pages, the United States Department of Energy guidance on attic insulation and ice dams, the American Red Cross winter storm safety advice, Natural Resources Canada and Health Canada pages on winter home safety, and the Canadian Mortgage and Housing Corporation guidance on ice dams. Guidance from the Met Office and local authorities in the United Kingdom was reviewed for snow and heavy weather advice. Where figures differ, the more cautious figure is given.

Learn first aid¶

A hands-on first aid course teaches you how to help someone who has been hit by falling snow or debris, has fallen from height or is buried. The Red Cross, St John Ambulance and local providers offer short courses, and many include CPR and bleeding control. Take one with your household before the next winter.

Related guides¶

• Heavy snow, ice dams and roof collapse
• Roof leak
• Shoveling snow safely
• Winter storm safety: home heating and cold survival
• Downed power lines and vehicle electrocution