Heavy snow on the roof can quickly make winter the homeowner’s worry. It is important to know the snow load and the potential for structural issues and safety, so you don’t have to worry. If you’re wondering what you need to know about snow load, we’ve compiled it all here.
What is Snow Load?
The downward force exerted by accumulated snow on a structure, usually a roof, is called snow load. However, this weight of snow can vary widely based on a number of factors, such as the depth or density of the snow, or the roof structure itself. Simply put, the more snow on your roof, the higher your snow load.
Factors Affecting Snow Load
- Ground snow load
It is the weight of snow that will fall on the ground in that particular geographic location. A ground snow load map is often built into local building codes, and this information can be found there. The design snow load for roofs is calculated from this ground snow load.
- Snow density
The water content of the snow (or density of snow, in terms of how much weight per unit volume) varies. Wet, heavy snow is more dense than light, fluffy snow. Light, dry snow a foot (ft) high could be but a few psf in weight; wet snow the same height could weigh much more. Snow density increases with successive (or near successive) snow melt and refreeze or after heavy snowfall followed by rain.
- Roof structure
How much you wind up with is based on how much snow is on your roof and at what angle. For example, flat roofs are quite different with respect to shedding snow from gable roofs. However, flat roof snow load is of particular concern because snow has a tendency to build up. Snow accumulation produces uneven loading on the roof, and snow loading is dependent on the slope of the roof.
- Elevation and latitude
More snowfall and therefore higher snow loads are found in general at higher elevations and latitudes.
- Areas of the roof
Uneven snowfall on roofs. Snow drift and accumulation are greater in areas of the roof near valleys, parapets, and lower roof sections. Such snow drifts produce a very considerable unbalanced snow load.
- Ice dams
Water infiltration can be exacerbated by ice dams (formed from melting snow refreezing at the eaves).
How Much Snow is Too Much?
Design snow load is based on geographic location and historical weather data, and is covered by building codes. These codes, often referencing ASCE standards, relate to ground snow load, roof slope, and other factors to establish appropriate roof snow loads for new construction. Usually, these codes are given in psf or how much surface area is covered on the roof.
I know many homeowners don’t know what the design snow load for their home is. The best advice is to consult with a qualified structural engineer or roofing professional, especially if you live in a designated snow country or have had heavy snowfall or even a blizzard, but a snow load calculator can give you a rough estimate.
Signs of Excessive Snow Load: Recognizing the Warning Signs
Knowing the signs of excessive snow load on your roof is crucial for preventing potentially catastrophic structural damage. Acting quickly upon noticing these warning signs can save you from costly repairs and ensure the safety of those inside the building. Here’s a more detailed look at what to watch for:
Visible Deflection (Sagging)
This is one of the most obvious indicators of excessive snow load. Look for:
- Sagging rooflines
Look at the roofline from the ground. If the roof is under great stress, you will notice a noticeable dip or sag, most often in the middle of long spans.
- Ceiling sagging
You can examine the ceilings inside your home. Check areas for sagging or bowing, especially in rooms underneath those which accumulate the most snow. This is a serious sign that the roof structure is deflecting under the weight of the snow.
Cracks in Walls or Ceilings
These cracks aren’t just cosmetic issues; they can signal structural stress:
- Interior wall cracks
Contact your USG Structural Engineer for new cracks or the widening of existing cracks in interior walls, especially around door frames and windows. Diagonal cracks are a problem, generally being a sign of movement in the structure.
- Ceiling cracks
If you notice cracks in the ceiling that run perpendicular to the roof rafters (or trusses), it means your roof is deflecting and placing stress on the ceiling below.
Sticking Doors or Windows
When a roof is put under too much stress, the building’s frame will start to slightly shift. This can lead to:
- Doors that are difficult to open or close
If doors that are supposed to be free-swinging start to bind or stick, it may indicate that snow load resulted in structural movement.
- Windows that are hard to open or close: Windows that cannot be opened or closed simply do not work; they also reveal households and businesses in which the frame of the building itself is stressed.
Excessive Noise (Creaking or Groaning)
Unusual sounds coming from the roof structure are a major red flag:
- Loud creaks or groans
You might hear loud creaking, groaning, or popping sounds — sounds of sheet metal moving under the roof’s heavy snow load. If you hear these noises, it means that the structural members of your roof are putting stress on them and are maybe starting to reach their load-bearing capacity.
- Sudden snapping sounds
Such a sudden snapping sound can be an indication that a structural member has snapped or will snap at any time. It is a very serious matter that needs to be taken care of now.
Water Leaks
While leaks can have various causes, they can be exacerbated by snow load:
- New leaks
If you suddenly discover new leaks in your ceiling, or any other new leaks that you were not aware of, especially if they occur after or during heavy snowfall, you may have a deflected roof allowing water to get through.
- More severe existing leaks
If you already have some leaks and after a snowfall the cracks really grow, then the roof structure could be stressed more.
Gutters and Downspouts Damaged or Distorted
When a roof is under significant stress, it can affect the attached components:
- Separation from the eaves
When one checks, do the gutters pull away from the eaves? It could be a roof deflection.
- Bending or twisting
Anytime there is any bending or twisting in the gutters or downspouts themselves, it could be a sign that they are overwhelmed by the moving of the roof.
It is important to do something if you notice any of these signs. If it is an emergency or you simply handle it yourself, don’t hesitate to contact Kelbie Roofing or a qualified structural engineer to assess the situation and prevent further damage. If it is a hazardous condition, then do not try to climb onto the roof yourself. Safety is paramount, so it must be prioritized.
Preventing Problems Related to Snow Load
- Regular snow removal: If you get heavy snow, carefully remove snow from your roof, especially if you have a flat roof and have seen a lot of snow build-up. When performing snow removal, be careful, and safety has to come first.
- Proper insulation and ventilation: Preventing ice dams can be helped by an adequate amount of attic insulation and ventilation.
- Professional inspections: Kelbie Roofing advises that regular roof inspections can identify possible structural problems before they snowball into serious issues.
- Consider the dead loads: Always remember that the roof is already supporting its own weight (dead loads). More weight from snow increases the total load.
Why Every Business Needs Professional Assessment
It is important to know how much snow load is out there and what it could do. If you feel that your roof may need some attention, whether it occurred following a heavy snowfall in December (or any other month in winter) or you are in an area where snowfall is common, you shouldn’t hesitate to contact Kelbie Roofing. We can carry out an assessment of your roof, provide advice regarding proper snow removal practices, and confirm that your roof is structurally sound. Not taking roof snow loads into consideration can be disastrous to your structure, including roof collapses.
Contact Kelbie Roofing Today!
Don’t wait until it’s too late. Contact Kelbie Roofing today for a professional roof inspection and peace of mind this winter. We’re here to help you navigate the challenges of heavy snow and ensure your home is safe and secure. Whether you have asphalt shingles or another roofing material, we can help. Let us help you protect your investment from the weight of snow and potential structural issues.