The Dangers of Snow Load: How to Prevent Roof Collapses in Winter
Everything looks different when it is covered in snow – it is almost magical. As snowflakes fall, you might be thinking about building the perfect snowman, but as a homeowner or property owner you should also be aware of the risks heavy snowfall poses to roof structures during winter.
The immediate threat of snow load is to the roof itself – shingles can be lifted, underlayment perforated, and the decking rotted. Unfortunately, the damage typically doesn’t stop there. As snow melts during the daytime when the sun is shining, it turns into water that sneaks and creeps beneath roofing materials. Although it might not be noticeable, over time this water can lead to mold growth and the degradation of insulation and internal structures.
When a roof is built to code, it should be able to withstand the maximum weight of snow that might accumulate in a particular geographic area. Two feet of snow on an average-sized roof can add nearly 20 tons of additional pressure to the roof. If the framing and structural support has not been designed to account for these conditions, it can cause catastrophic damage beyond simple roof collapse.
Understanding Snow Load and Its Impact on Roof Structures
What is Snow Load?
Snow load is the downward force on a building’s roof exerted by accumulated snow and ice. State building codes mandate snow load ratings based largely on historical weather data, specifically for wind speed/direction and snowfall.
Basically, snow loads indicate the amount of additional force pressing down on a building when snow and ice pile on a roof in the winter. Several factors influence snow load on roofs, such as:
- Snow Type: The specific type of snow, the way it accumulates, and weather that occurs between snowfalls, all contribute to the ultimate snow load condition. The weight of snow varies greatly – one foot of light dry snow weighs 3 pounds/ft2 while one foot of heavy wet snow weighs 21 pounds/ft2 (FEMA P-957 2013).
- Depth: If possible, you should measure the depth of snow on your roof. By using a snow load calculator, you can determine your risk by multiplying the density (lb by cubic ft) by the depth of snow (ft).
- Roof Design: Flat roofs are at the greatest risk from roof snow load damage, whereas a steeper incline (pitch) roof allows the snow to fall more easily off the roof. Experts suggest having a roof pitch of no less than 1:12 if you live in a heavy snow-prone area.
Risks of Excessive Snow Load
Snow accumulation more than building design conditions can result in structural failure and possible collapse. Structural failure due to roof snow loads may be linked to several possible causes, such as:
Often, the risks from accumulated and excessive snow load on roofs can be prevented by properly and safely removing snow from the roofs of commercial properties and buildings, as well as homes.
Luckily, there are warning signs of potential structural weaknesses. Here are a few ways to prevent roof collapse and roof structure safety.
- Detail the potential risks and consequences of excessive snow accumulation on roofs, including structural damage and collapse.
- Reference FEMA guidelines or similar authoritative sources for credibility.
How to Assess Your Roof’s Vulnerability to Snow Load
Identifying At-Risk Roofs
The type and condition of roofing materials can impact its strength. For example, older steel framed buildings used a cantilever beam layout to minimize the beam sizes by using the load of one beam to reduce the stress in the adjacent beam. Since snow buildup occurs in an unbalanced manner, roof failures have been attributed to this type of construction. Being aware of the type and condition of your roof can help with roof collapse prevention.
Overstressed roofs typically display some warning signs. Wood and steel structures may show noticeable signs of excessive ceiling or roof sagging before failure. The following warning signs are common in wood, metal, and steel constructed buildings:
- Sagging ceiling tiles or boards
- Sprinkler heads deflecting below suspended ceilings
- Popping, cracking, and creaking noises
- Sagging roof members, including metal decking or plywood sheathing
- Bowing truss bottom chords or web members
- Doors and/or windows that can no longer be opened or closed
- Cracked or split wood members
- Cracks in walls or masonry
- Severe roof leaks
- Excessive accumulation of water at nondrainage locations on low slope roofs
If you are unable to assess the vulnerability of your roof to snow load and you are worried about snow weight on roof, it is important to reach out to a professional to conduct an assessment. For commercial properties and buildings, a structural engineer can calculate the maximum snow load your roof can safely handle. Homeowners can contact roofing companies to identify if your roof is at risk. When considering hiring a professional, it is best to do so in the warmer months, so you can make any adjustments or renovations before the winter season.
Monitoring Snow Accumulation
As the snow starts accumulating, it is essential to monitor the snow depth on the roof and pay attention to areas where snow tends to drift. Examples of areas to monitor:
- In low roof sections adjacent to higher sections or structures
- On the downwind side of pitched roofs
- Against walls more than two feet high
- Against large roof structures more than 15 feet wide
One way to measure snow depth is by using a snow board. Snow boards are an excellent tool to help you measure snow. Basically, a snow board is a sturdy wooden board that you can lay on the ground in an open area to collect snowfall. Even a piece of plywood could do the job, but you will want to be sure that the board is level. By using this board and a ruler, you can record the amount of snow throughout the day in a journal.
Preventive Measures to Protect Your Roof from Snow Load
Safe Snow Removal Techniques
Snow removal can be dangerous, so before you try to perform roof snow removal yourself, you should focus on safe snow removal techniques.
To stay safe, stand on the ground and use a tool such as a roof rake to pull the snow down. To avoid pulling heavy, wet snow drifts on top of yourself, stand to the side of the roof on the ground while using the appropriate tools. Stay alert for falling icicles, too.
One effective approach to removing snow from the roof is by using de-icing products – like magnesium chloride. Some de-icing products can be applied without a ladder.
Another way to remove snow is with heating cables. Various heating cables, which can be easily purchased at hardware stores or online, are installed across your roof during milder weather. When turned on, the cable emits enough heat to melt the snow and prevent ice buildup.
Lastly, you could consider investing in an automated roof snow removal robot. These motorized robots use rubber track wheels to travel across the roof surface of your roof to break up or scrape off snow and ice with a rotating brush.
These methods are much safer than utilizing a ladder. Slips, trips, and falls are common dangers related to snow removal.
Strengthening Roof Structures
If your home or office is in heavy snowfall areas, you might want to concentrate on reinforcing the structure of your roof before winter. By strengthening your roof structure, you can protect your home from winter storms.
One way to protect and prepare your roof structure for winter weather is by scheduling regular inspections and performing routine maintenance to your roof throughout the year.
Other ways you can strengthen the structure of your roof is by increasing the load-carrying capacity of your roof system by reinforcing existing rafters or trusses. By increasing the thickness of your rafters, you can increase their ability to withstand sagging. Reinforcing the connections between the rafters and the walls will help prevent your roof from collapsing.
Developing an emergency plan to monitor and possibly remove snow from susceptible roof sections would be an appropriate action during a winter storm. The snow removal plan should be put into effect immediately after snow begins to fall.
Businesses should have a Snow Event Response Plan in place prior to the winter months that defines a way to determine snow load and at what point snow removal should be started. If you are a business owner or property manager, you should have a plan in place for in-house snow removal or have a snow removal contractor on retainer.
Professional Solutions for Managing Snow Load
When to Call the Professionals
Hiring snow removal contractors or companies can be expensive, but there are times where professional intervention is necessary. It is important to build a relationship with contractors well before the winter season. By creating these relationships, you can ensure that the contractor is in retainer, as they will be in high demand and difficult to find once a snowstorm begins.
When selecting a reputable snow removal provider, you should get multiple estimates so you can compare prices and services. Be sure to ask for references from their current customers and become familiar with their pricing.
BMS CAT’s Expertise in Roof and Snow Load Management
If your property experiences damage from a frozen water pipe, winter storms or snow load – BMS CAT is ready to help. With locations across the nation, we have helped thousands of homeowners and business owners restore, rebuild and recover their property after being damaged from winter storms and snow load.
Our teams are available 24/7/365, so contact us immediately if your home or business building has been damaged from winter weather.