Metal roofs are a common sight on steep roofs, but they can work just as well on low-slope roofs – provided the metal roofing system meets the minimum slope requirements set by the building code and the manufacturer.
So, if you’ve got your eye on metal as a replacement for your existing roof, you need to pick an option suited to your roof’s existing slope. Otherwise, you could be setting yourself up for leaks and a whole host of headaches down the road.
What Is the Minimum Slope for a Metal Roof?
Under the International Residential Code (which Utah uses as the basis for its residential building code), as well as manufacturer installation manuals, minimum slopes can range from 3:12 for certain metal roof systems down to 1/4:12 for some standing-seam systems.
The exact minimum slope figure for a metal roof depends on the type of metal roofing system you plan to install, which we’ll tackle a little further down.
A 3:12 slope means the roof rises 3 inches vertically for every 12 inches it travels horizontally. A 1/4:12 slope rises only a quarter of an inch over the same 12-inch run, making it an extremely low-pitch roof compared to the former.
Keep in mind, however, that the building code also requires metal roof systems to be installed in accordance with the manufacturer’s installation instructions. Thus, if a manufacturer’s minimum slope is more restrictive than the code, the manufacturer’s requirement takes precedence for that specific product.
Minimum Roof Slope by Metal Roofing System
You can’t choose a metal roofing system first and worry about slope later. The two have to match from the outset; otherwise, you risk water intrusion while potentially running afoul of code and manufacturer requirements.
Here’s a side-by-side comparison of common metal roofing systems and their minimum roof slopes for your reference:
| Roofing System | Minimum Slope |
|---|---|
| Exposed-fastener metal panels (e.g. R-panels, AG panels, and PBR panels) | 3:12; as low as 1/2:12 where the system is designed for applied lap sealant |
| Standing seam (snap-lock) | Commonly 3:12, although some products are rated for lower slopes |
| Mechanically seamed standing seam | As low as 1/4:12 on qualifying systems |
| Structural standing seam | Typically 1/4:12, but may be higher depending on the system |
| Metal shingles | 3:12 |
What’s the Lowest Pitch for Metal Roof?
The lowest pitch for a metal roof can be as low as 1/4:12, meaning the roof rises just 1/4 inch for every 12 inches of horizontal run. However, as you can see from the comparison table above, this applies only to certain structural and mechanically seamed standing seam systems.
How Do You Measure Roof Slope?
Method 1: Measure From the Roof
If you can access your roof safely, place a level horizontally against the roof surface with one end pointing upslope. Measure 12 inches along the level, then measure vertically from that point down to the roof.
If there’s a 4-inch gap, for example, you have a 4:12 roof slope.
Method 2: Measure From the Attic
If you aren’t comfortable working at height, measure from inside the attic instead. You can take essentially the same measurement from underneath the roof.
Place a level horizontally against the bottom edge of a rafter. Measure 12 inches horizontally from where the level meets the rafter, then measure vertically from the level up to the rafter.
A 2-inch rise over that 12-inch run means your roof has a 2:12 slope.
Method 3: Ask Your Roofer
If installing a new metal roof is on your agenda, your roofer can measure the slope as part of the roof inspection. More importantly, they can compare that measurement against local code and the installation requirements for the specific metal roofing system you’re considering.
Can You Increase the Roof Slope?
If you have a particular metal roofing system in mind but discover that it isn’t approved for your existing roof slope, it’s possible to increase the slope of your roof. In most cases, however, doing so requires reframing the roof by modifying or replacing existing rafters or trusses to create a steeper pitch.
Depending on the design, a contractor may also build a new sloped roof structure over portions of the existing roof.
As you can tell, we’re now crossing into the territory of structural work. This changes the roof’s geometry and typically involves modifications to the framing, roof deck (sheathing), flashing details, and other components, which require additional labor and cost. You’ll also need to account for local structural, permitting, and inspection requirements.
If you’re only considering increasing the slope because you want to install metal roofing, there’s no need to alter your roof pitch.
A better starting point is to determine whether there’s a metal roofing system approved for your existing slope (you can use our comparison table earlier as a guide).
For example, rather than rebuilding a 1:12 roof so it can accommodate a snap-lock standing seam system requiring 3:12, you may be able to install a mechanically seamed standing seam system that’s engineered for lower-slope applications.
Reframing your roof can make sense when you’re already planning a major renovation or need to correct drainage or structural problems. But it’s a fairly big undertaking just to accommodate a particular style of metal roofing.
Why Does Roof Slope Matter?
Roof slope matters because, first and foremost, it dictates how well water can flow off the surface and toward the gutters. If a roofing system is installed below the minimum slope required by code or the manufacturer, it may physically fit and look fine as is, but it won’t perform as intended. And that alone can come with all sorts of problems.
Leaks
One of the main concerns with low-slope roofs is that water moves much more slowly along the surface, buying it more time to intrude through vulnerable points such as panel laps, seams, and flashing. Imagine how much worse that could get if your metal roofing system is installed below its recommended minimum slope.
This matters even more for us in Utah, where we tend to experience heavy snow. For the same reason, snow can remain on a low-slope roof longer, giving melting water more time to pond and seep into vulnerable areas.
Rain accompanied by high winds can make matters worse by pushing water underneath laps and other connections.
You may not see a leak after the first storm. But given enough exposure, you could eventually find damp spots, water stains, or discoloration that indicates water intrusion.
Warranty Issues
Installing metal roofing below the manufacturer’s specified minimum slope can put your warranty coverage at risk.
Say the metal roofing system you choose has a manufacturer-specified minimum slope of 3:12, but it’s installed on a roof with a 2:12 slope. If you later develop a leak or another problem related to that installation, the manufacturer may have grounds to deny your warranty claim because the system wasn’t installed according to its requirements.
That could leave you paying a hefty bill out of pocket to repair or even replace the affected roofing.
Inspection or Permit Issues
A below-minimum roof slope, whether the result of a DIY approach or a roofing contractor who cuts corners, can come back to bite you during the permitting and inspection process.
An inspector may check whether the roofing material and installation comply with applicable building codes and the manufacturer’s instructions. If the system isn’t approved for your roof’s pitch, you could be required to correct the installation before the work passes inspection.
That’s an expensive problem to deal with when the new metal roof is already sitting above your head.
Reduced Roof Lifespan
The leak problems we discussed earlier don’t always end with fixing a drip. When a metal roofing system spends years performing under conditions it wasn’t designed for, the effects can gradually take a toll on the roof as a whole.
Moisture-related deterioration can affect fasteners, seams, flashing, underlayment, and eventually the roof deck. Repeated repairs can only go so far once problems become widespread.
You may find yourself replacing sections of the roof more often or, in more severe cases, replacing the entire system years earlier than you otherwise would have. That’s a poor return on a metal roof that’s supposed to serve your home for decades.
FAQs
What Is a Roof Pitch?
Roof pitch describes how steep a roof is, expressed as how many inches the roof rises for every 12 inches of horizontal run. For example, a 4:12 pitch means the roof rises 4 inches for every 12 inches it extends horizontally.
The term is commonly used interchangeably with roof slope, although there’s technically a distinction between the two. In stricter terminology, pitch refers to the roof’s vertical rise relative to the total span, or width, of the building beneath it.
Can You Install a Metal Roof on a Low-Slope Roof?
Yes, you can install metal roofing on a low-slope roof, provided you use a metal roofing system rated for that slope. As we covered earlier, certain mechanically seamed standing seam systems can be installed on slopes as low as 1/4:12.
However, low-slope does not mean flat. If your roof is truly flat, or close enough that water may remain on the surface rather than readily draining away, membrane roofing systems, such as TPO, EPDM, PVC, and SPF, may be a better fit than metal.
Can I Use Metal Roofing on a 2-12 pitch?
Yes you can, but you’ll need a metal roofing system rated for a 2:12 pitch. Certain standing seam systems can accommodate this low-slope configuration. Meanwhile, metal shingles and many exposed-fastener systems require a steeper roof.
Does Utah Require a Minimum Roof Slope for Metal Roofs?
The 2021 Utah State Residential Code (UTSRC) establishes minimum slopes based on the type of metal roofing system being installed. Guidelines are patterned after the 2021 International Residential Code (IRC). The applicable minimum also depends on the manufacturer’s installation instructions, which may require a steeper slope than the code minimum.
Is a Steeper Metal Roof Better?
While a steeper metal roof generally sheds rain and snow faster, a lower slope can perform just as well when paired with a metal roofing system designed for it. The “better” roof slope is one that works with your home’s design and does its job of keeping water out.
Need Help Finding the Right Metal Roof for Your Home?
Getting a professional roofer’s input can help you choose a metal roofing system that’s right for your home’s existing slope and overall structure. That way, you get the look you want without compromising the roof’s ability to keep water out for years to come.
That’s the approach Avail Solar has taken with hundreds of homeowners across Utah, including Salt Lake City, Murray, West Valley City, and surrounding areas.
Before we even think about installing a new roof, we assess what you already have and recommend a system that complies with Utah’s building code while taking your preferences into account. Book a call today to discuss your options, or request a quote for a metal roof installation!