How Roof Slope Affects Material Options and Function


The angle of your roof, known as the slope, is a crucial factor when deciding on the right roofing system and materials for your home. It does not only affect the way your roof looks; it has a significant impact on your home’s protection and interior. It dictates how well the roof functions over time and how efficiently it sheds water and debris. The slope also influences decisions like which roofing system and materials suit your architecture, costs, walkability, and design.

The slope determines how well the roof can shed water and debris. A steeper slope helps water and debris slide off, preventing leaks. If the way the roof is sloped is wrong, it could even void warranties and affect permits. Even if you’re not directly involved in choosing the slope, understanding its importance can guide your maintenance and roof installation decisions.

While various elements play a role in roof design, the slope is essential. Homeowners and contractors must consider it for roof installation and repairs. Keep reading to find out more about how it matters.

Different Slopes, Different Roofing Systems

Roofs are designed to protect all sorts of buildings. However, various factors, including the roof’s slope, determine the best roofing system. The angle of your roof matters whether you’re a homeowner, business owner, or roofing contractor selecting the right installation, repair, or replacement services.

What is Roof Slope?

a snowy roof

Roof slope is the angle at which the roof slopes. You measure it by looking at how high the roof goes up (rise) compared to how far it goes across (run). For instance, a 6:12 pitch means the roof rises 6 inches for every 12 inches it goes across.

Roof Slope vs. Pitch

Before we continue, let’s clarify two important terms. While “slope” and “pitch” are often used interchangeably, they actually mean different things in an architectural sense.

  • Pitch is about how steep the roof goes up compared to how wide it stretches. It’s shown as a fraction. The width of the roof is the distance between the tops of two walls.
  • The slope is about how steep the roof goes up compared to how far it runs horizontally. It’s shown as a ratio indicating how much the roof rises for every 12 inches it runs. The “run” is from one wall’s top to the center of the roof’s ridge.

In simple terms, pitch matters more for how the house is built, like for those doing the framing. The slope is more about the house’s design, seen from different angles on the house plans.

However, for homeowners and roof material suppliers, the difference between pitch and slope won’t matter much, and it can be used interchangeably.

How to Discover Your Roof’s Slope

When you look at floor plans, you’ll see the roof slope in drawings showing the front, back, and sides of the house. You’ll notice a right triangle near the roof with a number next to the up-and-down line and the number 12 on the line that stretches horizontally. (The pitch might be shown as a fraction in construction details.)

For an existing home, finding the slope is the best way to figure out the roof’s pitch. You can hire a pro, or you can do it yourself. It’s not too hard. Grab an 18- or 24-inch level, a tape measure, a pencil, and a can-do attitude!

In your attic, put one corner of the level against the bottom of a roof rafter and make sure it’s level. From that corner, mark the level at 12 inches with a pencil. Measure vertically from the 12-inch mark to the underside of the rafter just above it. Let’s say that number is 4. That means your roof rises 4 inches for every 12 inches it runs. So, your roof’s slope is 4:12 or 4 in 12.

Why Does Slope Matter?

a white modern farmhouse house with dark shingled roof

Slope matters most because of the weather where you live. Roofs are sloped to guide water, melt snow, and keep debris away. If you’re in a rainy or snowy area, a steeper slope helps handle the elements better. Generally, roofs in warmer places have gentler slopes, while colder places need steeper ones.

But slope affects more than that. It decides what kind of roofing material works best and how your roof looks. For example, a barely sloped roof might need metal or special asphalt to stop water from sneaking in, while steeper roofs can use shingles, wood, tiles, or metal. Different roof styles also need different slopes – think Prairie or Cape Cod.

How the roof is sloped can also affect the interior space available in a house. Steep slopes can give more attic space, while gentler ones don’t.

Slope affects the financial aspect of roof installation. Steep roofs use more materials, so they cost more to install.

One more thing: slope matters for strength. A not-so-steep roof can’t handle as much snow as a steeper one. That’s why those Swiss chalets in the Alps have such steep roofs: to carry all that snow.

Comparing Different Roof Slopes

Low-pitched (low slope) roof

low-pitched roofs in Italy

A low slope means the roof doesn’t rise more than 3 inches in every 12 inches. This kind is common for businesses and now for modern homes too. You’ll often find these on commercial buildings, although some architectural styles go for a flat look. This type of roof has three key parts: a weatherproof layer, reinforcing layers, and a surface material.

The weatherproof layer, usually made of stuff like thermoset or modified bitumen, can handle all sorts of weather and keep water and debris out. Reinforcing layers made of fabric add strength, durability, and resistance to sharp things. The top surface is what you see, and it makes the roof look good while adding extra protection.

Medium-pitched (conventional slope) roof

a single story home surrounded by trees

These roofs have a pitch between 4:12 and 6:12. They’re easy to walk on and work well for things like sheds or garages. No extra safety gear is needed for installation or repairs.

A conventional slope often uses asphalt shingles, slate, and metal as roofing material. Asphalt is the most commonly used for residential properties due to its durability, affordability, and ease of installation. Metal is also highly popular for its durability and lifespan. Meanwhile, slate is known for its longevity and beauty, as it can last up to 100 years or even more.

High-pitched (steep-slope) roof

a high pitched roof in construction

Steeper sloped roofs are designed to stop water and debris from gathering. A high-slope roof goes up more than 3 inches for every foot it goes across. Unlike flat roofs, you can see these roofs better, so they need coverings that look good and keep things dry. They’re often used for homes.

High-slope roofs have three main parts: the roof deck, underlayment, and roof covering. The roof deck supports the roof’s weight and structure (like the frame). The underlayment goes on the deck and protects against leaks and weather. The top layer of roofing material is picked based on cost and how it looks since it’s the most visible part.

Steep slope roofs matter a lot in home aesthetics. They’re a big part of how a house appears, sometimes even 40% of the outside. Steep roofs also tend to last longer. They’re great at getting rid of water and facing less direct sunlight.

The Pros and Cons of Low and High-Pitched Roofing

Pros of High-Pitched Roofs

A pitched roof naturally tilts a lot. And the steeper the roof, the better it is at letting rain, snow, and debris slide right off and away from your building. Check out some of the benefits of steep roofing:

  • Better water flow: Water falling on a steep roof heads straight down, off your roof, and into your gutters. No water pooling means your roof stays drier, preventing mold and increasing its lifespan.
  • Less snow and ice: Steep roofs aren’t just suitable for water but also great at stopping ice and snow from sticking around. If you’re in a snowy area, this is something to consider when picking your roof.
  • Extra storage room: Pitched roofs are often A-frame shaped; the steeper the slope, the more attic space you’ll have. If you need more storage, a steep-slope roof can give you that. You can even turn your attic into extra living space with the right slope!

Cons of High-Pitched Roofs:

Of course, there are some downsides to pitched roofs.

  • Harder to get on and move around in: Because of the steepness, moving on the roof is more challenging. This might mean more costs for repairs, installation, and maintenance of your roof. This also means it’s best to rely on professionals when handling roof jobs.
  • Better for residential buildings: These roofs aren’t great for big commercial buildings or large facilities.

Pros of Low-Pitched Roofs

Low-slope and flat roofs have their own benefits, too. Flat roofs are better for large areas. Low-slope roofs work for things like covered porches and decks. Check out more pros for low-slope and flat roofs:

  • Easier and cheaper to install: Flat roofs don’t need complex support systems, so they use less building material and cost less to install. Simplicity also means less labor cost. If a flat roof suits your design, it’s a cost-effective choice.
  • Energy savings: Steep roofs mean more attic space, but low-slope roofs cut that down. This affects how complex your heating and cooling system has to work. Low-slope roofs save energy by having less unused air space, keeping your building comfy without straining your HVAC system.
  • More ways to use the roof: While a steep roof gives attic storage, a low-slope roof gives you options to use the roof itself. You can even set up a sun deck on a flat roof, which is trickier than a steep one.

Cons of Low-Pitched Roofs:

But like pitched roofs, low-slope roofs have cons too.

  • Limited materials: The angle of the roof means you’re limited in materials (no shingles, tiles, or shakes) due to the low slope.
  • Not great for snowy or rainy areas: Low-slope roofs aren’t the best choice if you live in a snowy or rainy climate region, as these elements can pile up and cause structural damage.
  • High maintenance: Low-slope roofs need more care. They’re more prone to leaks and need more frequent inspections and maintenance.

Understanding Roof Slope

Roof slope, often called pitch, is figured out using “rise over run.” This means how much the roof goes up vertically. For every twelve inches, it goes horizontally. If a roof has a rise of four inches for every twelve inches of run, it has a slope of 4/12 (also written as 4:12). Here’s a list of common roof slopes and what they’re called:

  • Flat Roof: 2/12
  • Low Slope: 2/12-4/12
  • Conventional Slope Roof: 4/12-9/12
  • High Slope: 9/12 – 20/12
  • Very High Slope: 21/12 and higher

How Roof Slope Affects Your Roofing Material Choices

The roof slope plays a major role in how your roof is designed. Roofs are usually grouped into two main categories: steep slope roofing and low slope roofing. Steep slope roofs are commonly seen on houses, giving them their residential look. On the flip side, low-slope roofs are more often found on commercial buildings, although many modern homes also have them.

Knowing your roof’s slope helps you choose the right roofing materials and the best way to put them in place. Since there’s a wide range of roofing types and materials out there, there’s no set standard for roof slope. Manufacturers usually suggest the minimum slope for their materials, but it’s the experienced installer who will suggest the best product for your specific slope. Every roof is different, and your contractor will guide you.

Flat roofs, often found on commercial buildings, are often made of built-up roofing, where layers of tar paper and hot tar create a waterproof seal. Steeper roofs suit asphalt shingles, wood shakes, and slate. Metal roofs are an interesting exception – they’re seen on both flat industrial buildings and modern homes, as well as on practically vertical roofs.

Remember, your roof’s slope matters when it comes to picking the right roofing material and style. Your contractor will help you find what works best for your unique roof.

Important note: If you want to change your roof’s slope – like adding slope to a flat roof – you’ll need a permit to follow local rules. Usually, if you hire a roofing contractor, they’ll handle permits for you before starting the work.

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