Weather affects everyone and every project.
It doesn’t matter if your project is in a region that gets 100+ degree temperatures, several feet of snowfall, or somewhere in between — there are weather-related design considerations to keep in mind.
Designing a standing seam metal roof according to the weather events it will experience helps to ensure the roof doesn’t prematurely degrade or fail due to the environment. Plus, it protects the often significant investment of the property owner and/or client you’re working with.
Sheffield Metals offers a wide variety of services and design assistance to architects, spec writers, and other design professionals, so we know how weather can influence what products and systems to use in a project. That’s why we have a in-house Architectural Department who can assist you during the crucial design phase to make sure the system will work for the environment.
In this article, we’ll discuss some of the most important warm and cold weather climate design considerations. Before we begin, we recommend reading through both the hot and cold weather design considerations listed below, as it could help you verify that all design angles are considered.
Metal Roof Design Considerations for Warm Weather Climates
Consideration #1: Cool Metal Roofing System
One of the first notable design considerations for a property exposed to extreme heat is to ensure that you’re installing a cool metal roofing system.
Cool metal roofing is defined as painted or coated metal products that reflect the sun’s energy to dissipate heat. Cool roofing ensures that heat is adequately transferred off of the metal’s surface so the cooling system doesn’t burn up as much energy trying to keep the indoors at a comfortable temperature. According to the Green Building Alliance, installing cool roofing can result in total cooling cost energy savings ranging from 7% to 15%.
Despite the common belief that cool metal roofing is a particular type of metal, the “cool” properties are dependent on the paint system applied during the coating process. The cool metal roofing paint/resin formula (formulated by Sherwin-Williams or another paint supplier) contains innovative solar reflective pigments.
Also, you’ll want to verify the metal has the appropriate:
- Solar reflectance – Solar reflectance is the ability of a material to reflect solar energy from its surface back into the atmosphere. Solar reflectance is measured in decimals on a scale from 0 to 1, where 0 would be considered the truest black and 1 would be considered the truest white.
- The measurement of solar reflectance is also dependent on a roof’s slope.
- Emissivity (also called thermal emittance) – Emissivity measures how efficiently and quickly a surface releases/emits absorbed heat and returns to its normal temperature. Emissivity is determined on a decimal scale from 0 to 1, where a 1 represents the most emissive material possible.
- Look for metal coil or panels with a higher emissivity value so the heat can’t linger on the surface and transfer indoors.
- Solar Reflectance Index (SRI) – Solar Reflectance Index is a measure of a surface’s ability to reflect the sun’s solar energy (solar reflectance) and emit heat (emissivity). SRI is measured on a scale from 0 to 100. An SRI value closer to 0 indicates a darker or black surface, and a value closer to 100 indicates a brighter or white surface.
- For a building in a hot climate, the higher the SRI, the better.
Consideration #2: UV Exposure Protection
Another essential component of installing a metal roof in a warm location is choosing metal products coated in a paint system that can withstand excessive UV exposure. In the United States, this is a common design concern in Florida, California, Texas, and other states where the sun shines for most of the year.
Unfortunately, the reality is that there will be some level of fading to expect on a metal roof, especially if it’s consistently exposed to the sun and high temperatures. However, that doesn’t mean the metal’s paint system’s fading or degradation has to be excessive.
You’ll want to ensure that you’re choosing or specifying metal with one of the following paint finishes:
- Polyvinylidene fluoride (PVDF) – This resin is made up of about 70% PVDF and 30% binders, solvents, pigmentation, and additives. Commonly referred to as Kynar 500® or Hylar 5000®, PVDF resins are the best protective coatings available to stand up to extreme temperatures, sun exposure, oxygen, humidity, and even pollution particles. Coils coated in this resin are most likely to have the most extended chalk and fade warranties (typically up to 30 years). Still, they are slightly more expensive due to superior durability.
- Silicone-modified polyester (SMP) – SMP coatings are a step below PVDF in terms of quality and warranty options. These consist of a combination mixture of polyester and silicone materials. SMPs are a great option to defend against extreme weather (including UV exposure) while still carrying long paint warranty options. However, SMP warranties often have a lesser chalk and fade rating than the PVDF.
One of the best ways to see how the manufacturer expects the paint system to last, especially when exposed to UV, is to read the warranty documents thoroughly. This includes all of the inclusions, exclusions, and other special conditions. Most reputable manufacturers make their paint specifications available so you can see how the coatings performed when tested in extreme weather conditions (i.e., accelerated weather testing).
Consideration #3: Fire Resistance
In regions where hot and dry weather conditions can create a concern for fires, installing a fire and combustion-resistant roofing material is critical. Recently, there have been wildfires ravaging California and its surrounding regions, which is why more and more manufacturers are emphasizing the production of fire-resistant building materials. Installing fire-rated building materials can help to prevent buildings from catching fire and spreading the fire to other structures.
Regarding standing seam metal roofing, you’ll want to look for metal that is tested according to the UL 790 standard and achieves a rating of Class A (the best/highest fire rating). Earning a Class A rating means that:
“Roof coverings are effective against severe fire test exposures. Under such exposures, roof coverings of this class afford a high degree of fire protection to the roof deck, do not slip from position, and are not expected to produce flying brands.”
Consideration #4: Tested for Uplift Resistance, Hail Resistance, and Location-Specific Codes
Going along with the fire resistance is the need for a standing seam roof system that is tested to stand up to weathering events that can wreak havoc on a roofing system. This can include wind (hurricanes, tropical storms, tornadoes, etc.), hail, and rain (wind-driven rain) in hot weather environments. Plus, you might even live in a state, county, or municipality that must adhere to region-specific codes and testing requirements.
Let’s dive a little deeper into some extreme weather events and the testing standards to look for if your project is located in a region where it may occur.
Wind & Wind Uplift Testing (UL 580 & UL 1897)
For properties where hurricanes, tornados, and other strong wind events are a threat, you’re going to want to choose a standing seam metal roofing assembly tested according to UL 580. This standard tests the uplift wind resistance of a metal roofing system, including the panels, accessories (clips, underlayment, and fasteners), and structural support frame. The test applies positive and negative pressure (PSF) and is a pass or fail test done in three UL 580 sequences and then turns into a UL 1897 if it can go beyond Class 90 and tests until the system fails:
- UL 580 Class 30
- UL 580 Class 60
- UL 580 Class 90 (best of the UL 580 test requirements)
- UL 1897 test (maintains a positive pressure and increases in negative pressure usually in increments of 15 PSF until the system fails)
Hail & Impact Resistance Testing (UL 2218)
For areas where hail is a concern, including Texas and the Great Plains, always ensure the roof system you’re installing adheres to the UL 2218 industry guideline. This test exists to measure a metal panel’s resistance to puncturing or failing when it comes into contact with items, such as hail or other small debris.
The final rating is on a scale from Class 1 to 4, with Class 4 being the toughest/least likely to fail when in contact with objects.
Rain & Water Intrusion Testing (ASTM E1646) / Wind-Driven Rain Testing (TAS 100)
ASTM E1646: In warmer regions that receive significant rainfall, such as the Southeastern U.S., you’ll want to pick a panel system with a passing ASTM E1646 water penetration rating. After the pre-determined air pressure is reached, water is sprayed on the panels for 15 minutes. The amount of ponded water is determined, and then the amount of water infiltration through the tested panel is measured. This is a pass or fail test where any water intrusion in the system will result in failure.
TAS 100: The less common rain-related test standard is TAS 100, which measures how a roof system holds up in wind and wind-driven rain conditions. TAS 100 is a region-specific test that will vary heavily from project to project. Check with your local building codes to see if this test is a requirement.
Special Codes, Testing, Requirements Based on Location
It’s also critical to remember that many cities, regions, and states have specific building codes based on the location’s weather patterns. This means that the roof or wall system you design with must adhere to these regulations and requirements. Some of the most common location-specific regulators include:
- Florida Building Code (FBC)
- Additionally, verify if your project is in a High Velocity Hurricane Zone (HVHZ), which is built into the Florida building code. Other states have similar codes and test protocols that fall under another name, so it’s best to check your state building codes or consult with a licensed contractor.
- Miami-Dade County building codes
- Texas Department of Insurance (TDI)
- International Code Council Evaluation Services (ICC-ES)
Consideration #5: Proximity to Coastline or Large Body of Water
One other consideration that often comes into play for warm weather environments is the property’s proximity to water, especially a coastline or saltwater environment. It’s recommended that all properties within a certain distance of a coast that contains saltwater use an engineered aluminum roof system (plus the proper accessories) and NOT a Galvalume system. Aluminum can better resist corrosion and rusting from saltwater, and still comes with a substantial paint warranty.
At Sheffield Metals, we recommend using an aluminum system:
- Within 1500 feet of a coastline with breaking surf
- Within 800 feet of a coastline with a large bay
- Within 400 feet of a coastline with a marsh
Metal Roof Design Considerations for Cold Weather Climates
Consideration 1: Snow Shedding & Retention Systems
Snow is easily one of the most significant concerns for properties in regions where cold weather is typical. When it comes to snow build-up on a roof, the number one main concern is the safety of the people inhabiting, entering, and leaving the building. Plus, you want to minimize any damage that falling snow can inflict on the property below, including windows, doors, cars, plants, etc.
This is why it’s critical to design the roof system with the appropriate snow shedding or retention system for your roof. According to S-5!, a Sheffield Metals partner and one of the best manufacturers of snow retention systems in the world, using a metal roof snow guard helps to retain the snow on the top of the roof and allows it to slowly leave the roof in small amounts or as melted water. Such systems are specifically designed to prevent catastrophic events from happening if the snow comes off the roof like an avalanche.
In regions with the threat of snow build-up, always make sure to design the roof with a steeper pitch/slope that allows for snow retention over walkways, doorways, garages, and any other areas accessible to people or property that can be damaged.
There are various snow retention systems to choose from that match the design of a roof and are warranted. Plus, snow retention and shedding systems can be installed without ever penetrating the roof’s surface, which is always recommended for standing seam metal roof systems.
Consideration #2: Ice Dam Prevention
Another cause for concern in cold environments is the potential for ice dams to form on the roof’s eave. Luckily, one of the benefits of choosing a standing seam metal roof for your project is that it significantly reduces the likelihood of ice damming from occurring.
Metal roofs, especially the lines of a standing seam metal roof, allow water to flow freely off the roof’s surface, which can help stop the formation of ice dams. Plus, with the proper ventilation for your whole roof system, you can avoid the formation of ice dams altogether in some cases. To learn more about metal roof ventilation and how it can be applied to your metal roof, check out this video.
Additionally, If ice damming is a concern, always make sure to install an ice and water shield type of underlayment beneath the panels. This will help to prevent water from entering the structure.
What Is an Ice Dam & How Does it Occur?
The attic is a collector of heat, which warms the roof and can help to melt snow off the surface. However, because the eave doesn’t have any attic space beneath it, it stays colder than the rest of the roof. As the snow begins to melt off the roof because of the warm attic, it freezes to ice at the cold eave. This creates an ice dam that builds up and prevents water from shedding off of the roof.
When the water has nowhere else to go, it just sits on the roof and often finds its way into the structure. Ice damming is common with asphalt shingles because the backed-up water is forced to flow underneath the shingle(s) and into the property.
Consideration #3: Underlayments Designed for Cold Weather
As far as underlayment goes, there are several considerations to keep in mind, especially in colder environments.
Ice & Water Shield Underlayment
First and foremost, we recommend using a full ice and water shield underlayment, a waterproof membrane product that protects vulnerable areas on a roof from water and ice damage. Such regions include eaves, valleys, hips, penetration points, and any other spot on the roof susceptible to water or ice intrusion.
If you’re going to use a synthetic underlayment, the roof pitch needs to be a 3/12 or more. Even so, we recommend using an ice and water shield in conjunction with the synthetic at the vulnerable areas mentioned above.
Temperature Restrictions
Many underlayments have a minimum outside and surface temperature that it needs to be for them to be correctly installed. For example, ice and water shield products have a peel-and-stick adhesive backing that runs the risk of not adhering to the roof deck if installed at a temperature below 40 degrees.
Always verify the minimum installation temperature and any other temperature restrictions that can influence your underlayment choices.
Slope & Substrate Requirements
No matter the environment, it’s important to always check the minimum slope requirement for the underlayment you specify. Some underlayments, ice and water shield included, might not go to as low of a slope as you would think. It’s critical to check the manufacturer’s instructions and follow them accordingly.
The same goes for ensuring that you can use the underlayment on your project’s specific roof deck substrate. Most underlayments can be installed over plywood or OSB decking, but not all are suitable for metal decking (B-deck), concrete, etc.
Consideration #4: Proper Structural Support
Another essential safety measure to consider when it comes to roofing snow build-up in colder regions involves the proper structural support underneath the standing seam metal roof.
It’s often easy to forget that snow is water, and water is heavy. So when you’re designing the building for the roof to go on, always make sure that the property has an adequate snow load capacity so it can handle the weight of snow and water. This is especially true if you have a snow retention system that keeps the snow on the roof so it can safely run off over time.
Our best recommendation is to involve a structural engineer who can look at the plans and ensure that the structure can withstand the weight.
Consideration #5: Proximity to Coastline or Large Body of Water
As discussed in the hot weather metal roofing concerns, the same principles apply to coastal properties in cold weather environments. Any property within these saltwater coastal distances should install an engineered aluminum roof system (plus the proper accessories) and NOT a Galvalume system:
- Within 1500 feet of a coastline with breaking surf
- Within 800 feet of a coastline with a large bay
- Within 400 feet of a coastline with a marsh
Final Thoughts on Metal Roofing & Weather
It’s safe to say that weather can significantly affect how you design your projects that have a standing seam metal panel system. But, If you know what to look for based on your location and weather patterns, you’ll be well-equipped to design a long-lasting metal roof that will make you and your client happy.
As a quick recap, remember to consider:
- Local or state-specific codes and testing requirements
- Special environmental concerns (UV, fires, water, ice, etc.)
- Proximity to an ocean, sea, or saltwater coast
- How a design can affect the safety of humans (especially from shedding snow)
Have another weather consideration and how it might affect what type of metal roofing system to use for your project? The Sheffield Metals Architectural Department is made up of highly knowledgeable individuals who have significant experience in the installation, design, bidding, and technical side of the architectural metals industry.
We’d love to hear from you — contact our Architectural Department today!
