There’s a lot that goes into making architectural decisions about your home. Whether you’re building from scratch or renovating, it’s an opportunity to act in ways that improve the functionality, aesthetics, even the value of the property. The approach you take to the roof is no different in this regard. The right roof can make or break the overall impact of your home.
You’ll even find that some of your decisions in this regard will also have a knock on effect on others. One of these is how your choice of a metal roof informs not just the color but also the silhouette and safety of your property. This is because in order to both be effective and conform to safety standards, there is a minimum slope required for a metal roof. Knowing how and why this is so can help you to make better architectural decisions for your home and make sure that everyone in it stays safe for years to come.
Let’s explore the matter further. Why is this something that makes a difference and how can you best go about applying standards in a way that fits your other priorities?
So, what is the minimum slope for a metal roof? Well, first it helps to understand a little about how the slope is measured. The gradient is known as pitch, which is calculated by how many inches a roof rises for every 12 inches of its depth. So, if the roof slope went upward 4 inches for every 12, the pitch would be described as 4:12.
The next thing to understand about the minimum slope requirements is that it can actually depend on not just the material but also the method of construction being used. This takes into account how secure the panels being used will be and how this impacts the roof pitch.
Chapter 15 (Roof Assemblies and Rooftop Structures) of the 2012 International Building Code makes the following stipulations with regard to minimum slope for a metal roof.
- The minimum slope for lapped, non-soldered seam metal roofs without applied lap sealant shall be three units vertical in 12 units horizontal (25-percent slope).
- The minimum slope for lapped, non-soldered seam metal roofs with applied lap sealant shall be one-half unit vertical in 12 units horizontal (4-percent slope). Lap sealants shall be applied in accordance with the approved manufacturer’s installation instructions.
- The minimum slope for standing seam of roof systems shall be one-quarter unit vertical in 12 units horizontal (2-percent slope).
This means the pitch for lapped, non-soldered seam metal roofs is 3:12. For lapped, non-soldered seam metal roofs it’s 1.5:12. For standing seam metal roofs it’s 0.25:12.
Why Is This Important?
When building a home, there might be certain silhouettes or aesthetics in mind for your property, that a steeper roof doesn’t fit in with. So why is it important that you shift your plans to allow for a different pitch, rather than taking a risk? Well, there are a few elements that you should be cognizant of.
Probably the most important reason to make sure you get the minimum slope for a metal roof right is the potential for water damage. Some metal roofs have better resistance to water damage than others, but when you choose the correct pitch for your roof you can help minimize any need for roof repairs. This is because roof pitch helps fluid run away from the metal surface of the roof and toward the gutter system. This is especially important when you have a more complex roof design that has various peaks and valleys — water can tend to collect at the base of each valley. A steep enough pitch helps it to run away effectively.
Snow can prove problematic for metal roofs. This isn’t just from the perspective of the potential for moisture to cause rusting, either. On low metal roofs, a buildup of snow can put additional pressure on the panels for a period of time, in areas of your roof that aren’t supported by the underlying structure this could dent the panels, or cause the metal to sag. With the correct roof pitch, your metal roof will prevent snow from building on the surface, and to slide off efficiently. The addition of snow guards can also help to make sure this process occurs safely.
Debris Build Up
When it comes to metal roofs, the problem of debris is largely an aesthetic issue. After all, you’re generally less likely to get the problems with rotting, mold, and mildew — although this isn’t impossible. However, the correct roof pitch helps to make sure that there are fewer areas that debris is likely to gather. This means there is less need for you to frequently get up on the roof and clean out the build up.
Home owners don’t always know just how vital the right ventilation in the roof space is. Even if you have a roof made of metal that is less susceptible to mold and mildew, insufficient ventilation inside the attic can lead to the underlayment and roof structure being negatively affected by these elements. This can especially be the case if you live in a humid climate. A sufficient roof pitch can help to make sure that there is a good amount of air circulation throughout the attic space. Indeed, your roofing expert will be able to accentuate this by making sure the underlayment materials are installed to prevent moisture problems from poor ventilation.
How to Measure and Check the Slope
Ascertaining the minimum slope for your metal roof is not a complex task. Though, ideally this should be planned before the roofing construction, and included as part of the architectural plans. However, if you have concerns that your roof pitch is not quite correct, or you’re considering making adjustments, there are reasons to check the current pitch of your frame. A roofing expert will usually have tools designed for accuracy — like a speed square, or a digital pitch gauge. But you can usually be relatively accurate yourself.
- Take an 18” or 24” level. Make a mark at the 12” point, either with a pencil or a piece of tape.
- Head to your attic, and place the level at the lowest point of the roof rafter.
- Holding the level exactly horizontal, take a tape measure and place it at the 12” mark. Then measure the distance vertically between the level and the rafter.
- You now have the pitch measurement. If the distance between the level and the roof is 4 inches, this means the pitch is 4:12.
If the pitch doesn’t meet the minimum slope for a metal roof, then you may need to seek professional assistance to set it right. This is no mean feat, requiring the roof to be stripped to its rafters and trusses, and either replacing parts of the frame entirely or making additions to adjust the angle safely and correctly. Not something to be taken lightly or attempted without expert guidance.
Achieving the correct minimum slope for metal roofing is not just a matter of getting great aesthetics — although that can be a part of it. It also helps to make sure you are able to mitigate against the variety of issues that can arise when the pitch is too shallow, from gathered water to undue pressure. While it’s easy enough to measure and check whether you have the right pitch, remember that adjustments should only be undertaken by a professional.