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It’s a well-established fact that metal buildings are strong and durable and serve as an excellent option for cold and snowy climates. However, to ensure maximum advantage, roof maintenance and snow removal should be performed regularly.
A number of factors are considered for the optimization of metal panels in such conditions. For instance, a proper design at the outset is required to avoid drift zones and cold spots and hot spots within the roof system to prevent water from freezing and thawing, causing ice buildup.
Additionally, roofs should be inspected before the onset of the winter season so that already existing issues with the roof can be addressed before they turn severe when snow and ice accumulate on the roof.
Though properly designed metal roofs have a history of performing well in the winters, heavy snowfall could be detrimental to buildings of all kinds. Such situations can pose dangerous risks to people living and working in and around such buildings.
This article will explore the weather conditions and considerations that can affect the performance of metal roofs and walls, and examine the steps to be taken to mitigate any potential negative effects in the snow and ice-prone areas.
Contents:
1. Anticipate Snow Load
In places receiving snowfall, snow gets accumulated on all types of roofs, which results in an increased amount of weight being borne by the structure. This increased weight (snow load) is dangerous to the structure and its occupants. If the weight of the snow or ponded water from melted snow exceeds the structure’s bearing capacity, it makes the roof or even the entire structure susceptible to collapse.
From the standpoint of structural engineering design, a metal roof should consider the specific code-required levels of snow accumulation for the building location. This ranges from 4.5-9 kg per square foot (psf) to over 18 kg per square foot. An engineer can design the roof structure to determine the loads acting on the roof based on the snow load. Consult the International Building Code (IBC) and state and local codes for guidance based on your location.
Additionally, it should be noted that the amount of snow can’t be translated easily due to the variations in snow density (i.e., light and fluffy vs. wet and heavy). Therefore, something less than 2.2 kg per square foot per inch of depth for very wet or heavy snow can be considered a conservative estimate.
If the roof is designed to accommodate a snow load of 9 kg per square foot, then any buildup over 4 to 5 inches can be a cause for structural concern. A structural engineer can determine the building’s carrying capacity and a reasonable range of snow density and weight. The key takeaway is to be aware of the weight your structure can bear and remove snow to keep it within safe limits.
2. Prevent Sliding Snow
The accumulated snow may slide down the roof’s slope (shedding) and cause injury to people and damage to property. However, snow shedding is essential to keep the snow load from accumulating beyond the building’s structural limits.
Balancing snow load and shedding is necessary and requires the geographical and building material and roof design factors to be considered. Roof pitch can make a significant difference in all aspects of snow buildup on a roof. Higher slope roofs, i.e., greater than 3:12, can accelerate the sliding snow with dangerous consequences.
For instance, accumulated snow falling onto an exterior gas line could rupture the pipes, which could prove to be a fire hazard with the smallest of ignition sources. Also, the weight of sliding snow can propel any icicles formed on eaves by the force and weight of sliding snow to fall onto people and property below.
On the other hand, low slope roofs (less than 3:12) offer less resistance to sliding because of low amounts of friction. Striations and embossing on metal roofing provide better resistance to sliding, especially when running traverse to the slope.
Though it could seem like a complicated procedure, the installation of metal panels with snow retention devices on a steeply-sloped roof is recommended. This will naturally shed snow and ice from the roofs and protect the structure from excessive snow loads.
3. Prevent Ice Dams
Ice dams are ridges of ice that form at the edge of a roof. They prevent the melting snow from draining off the roof, resulting in costly damages to structures. In order to prevent the formation of ice dams, it is crucial to understand its causes so that appropriate steps can be taken.
Most ice dams are formed as a result of building air barrier flaws. When warm air from the indoors escapes through a rooftop, the roof sheathing gets warmed up. This rise in temperature causes the underside of the layer of snow on top to melt.
The melted snow moves down the slope of the roof toward the eaves and freezes into ice. As this process continues, the ice gets thickened and takes the form of ice dams that trap water, which can travel into seams between panels and around flashings.
These blockages could cause the water to accumulate and form a reservoir that can possibly damage the roof system or leak due to excessive snow and ice buildup. Additionally, a peel and stick membrane can be used on the roof deck, spanning from the eave to about 3 feet up-slope from the exterior wall.
Preventive steps, like framing the roof with raised heel trusses, can also help prevent ice dams. Avoiding the inclusion of valleys and gutters that are at or above the roofing plane is ideal. These should be a priority when designing, installing, and maintaining a metal roof.
4. Use Retention Systems
Retention systems like snow fences, bars, or guards, can make the snow and ice melt completely or fall from roofs in small amounts. Such options can reduce risks associated with sudden rooftop avalanches. It is essential that snow retention systems are carefully engineered and properly installed.
5. Protect Roof Attachments
The force of sliding snow is strong enough to take off attachments like exhaust vents. To prevent this, the shear load should be reduced by installing rigid vent pipes as high up on the roof slope as possible. Otherwise, the pipes should be protected with a snow retention system.
6. Proper Snow Removal
Build up of snow on the roof could prove to be dangerous to the safety levels of the loads. Therefore, standing snow should be removed after a winter storm to ensure the loads are at safer levels. It is especially more important for older homes where poor attic insulation can form ice dams.
However, care should be taken while removing the snow, i.e., with metal or sharp tools, as this could cause serious damage to the metal roof. Experts advise that only the excess snow should be removed while leaving a thinner layer on the roof to melt and disperse on its own. Also, the snow should be removed uniformly from the entire surface of the roof, starting from the areas of accumulated snowdrifts and then moving evenly across the roof.
7. Additional Consideration
1. Roof Material and Surface Color
Metal roofs can quickly absorb heat and radiate it effectively. Darker colors can enhance the effect of solar absorption. But it becomes difficult for the snow to stay solid when UV light combines with heat loss through the roof.
Therefore, to prevent ice damming, the roof system should be properly sealed and insulated. Otherwise, it can result in ice damming, and the continuous melting and re-freezing of snow can form icy layers that promote snow sliding irrespective of the roof material or color.
2. Watertightness
The low-sloped roofs should have watertight panel seams to prevent water (melted snow) from leaking into the structure. It should be considered to use panels that have passed the ASTM 2140 water head test or FM 4471 Appendix G water test, and water-resistant underlayment should also be considered for all roof slopes.
3. Roof Layout
Roof designs like valleys and slope changes can cause the snow to accumulate and increase the snow load. The roof structure is prone to unbalanced sliding snow if the dormers extend from a large roof area and if one area is significantly larger than the other.
This imbalance can cause the standing seams to tear open and displace the panels. Also, the drifting snow can remain behind HVAC units, at perimeter walls, and behind solar and photovoltaic (PV) panels.
4. Roof Maintenance
In regions receiving heavy snowfall, it is of utmost importance to conduct regular roof inspection and maintenance works. Removal of standing snow and preventing the formation of ice dams is crucial in avoiding damage to the metal panels.
5. Warranty Considerations
If problems occur, it is better to consult the roofing material manufacturer for recommendations and warranty claims. It is advisable to check the metal panel manufacturer’s warranty to ensure that no products or tools are being used that will void the warranty of the product.
FAQs
From the standpoint of structural engineering design, a metal roof should consider the specific code-required levels of snow accumulation for the building location. This ranges from 4.5-9 kg psf to over 18 kg psf. It is recommended to consult the International Building Code and state and local codes for guidance based on your location.
Ice dams are ridges of ice that form at the edge of a roof. They prevent the melting snow from draining off the roof, resulting in costly damage to the structure.
Some of the examples are snow fences, bars, guards, etc. which make the snow and ice melt completely or fall from roofs in small amounts.
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