What You Need to Know About Roof Pitch

Understanding Roof Pitch and Why It Matters

 

How many times does a roof come up in conversations about a dream home?

Let’s face it … not too often, if at all.

People talk about an open concept floor layout, sparkling white kitchens with huge kitchen islands, lavish master suites with state-of-the-art bathrooms, outdoor spaces, and every imaginable part of a home. However, one of the most important features of a home – the roof, particularly the pitch of the roof – is overlooked.   

Why should we pay attention to roof pitch? For starters, the pitch of your roof, or the slant, is a factor that is critical to many aspects of a roofing system, including the choice of roofing material and accessories such as gutters. It can also affect the look of the home. In fact, certain pitches (shallow or steep) are integral to some architectural styles.

Because pitch is vital to the roof, it's essential to understand its purpose and what it means for the longevity and safety of the structure over our heads.

 

What Is Roof Pitch? 

In simple terms, roof pitch refers to the slant or steepness of a roof. It denotes the ratio of the ridge height to the width of a building and is commonly expressed as a fraction. For example, if you want a fairly steep pitch of 1/3 on a roof that is 45 feet wide, the roof’s height will have to be 15 feet.

In residential homes, the most common roof pitches range between 1/6 and 1/2. The higher the value of the fraction is, the steeper the roof will be – and the more visually pleasing and appealing.

 

How Is Pitch Different from Roof Slope?   

You may notice that in many instances the term slope is used instead of – or interchangeably with – pitch when describing the roof’s slant. However, they are different from each other and do not mean the same things.

• The pitch of a roof is the measurement of the rise of the roof – or ridge height – to the span, which is the distance from one wall’s top plate to another wall’s top plate and stretches across the width of the roof. A roof that rises 5 feet over a 30-foot span has a “1 to 6 pitch,” which can be written as a fraction: 1/6 pitch. One that has a ridge height of 10 feet over a 30-foot span has a 1 to 3 pitch, or 1/3 pitch. The larger the fraction, the steeper the roof. Pitch relates more to the actual house construction and is really meaningful only to framers.

• The slope of a roof is the measurement of the rise of the roof in relation to its run, which is the distance from the outside of one wall’s top plate to a point directly below the center of the ridge, and it denotes the number of inches the roof rises vertically for every foot it extends horizontally. For example, a “6 in 12” roof is one that rises six inches per 12 inches of horizontal run. In residential homes, the most common roof slopes range between 4 in 12 and 6 in 12. The higher the first number, the steeper and the more visually appealing it is. While the pitch is expressed as a fraction, roof slope is commonly represented in a ratio format – as in inches per foot (3:12, 4:12, 6:12) – or as the phrase “3 in 12,” “4 in 12,” “6 in 12,” and so on. Sometimes you’ll see the slope expressed as a fraction – 3/12, 4/12, 6/12 – but this is actually incorrect.

 

Historically, roof pitch is an older term than roof slope and was devised when the ridge of a roof typically came at the center of the span. Over the years, and especially in the past century or so, architects began designing homes and other buildings with asymmetrical roofs, in which the ridge is offset to one side. In these cases, the pitch doesn’t apply because it demands symmetry, so the building must be built with two or more pitches, creating confusion. In these cases, and in general, when specifying materials like shingles or discussing roof design in general, the slope is the more useful term – and concept – to use. This is because there are more – and easier to understand – gradations in roof slope, making specifying materials easier. (See the diagram below.)

 

Why Is Roof Pitch – and Slope – Important?

Considered the major component in roof design, the angle – steep or shallow – has a big impact on the roof’s appearance, durability, and weather performance. It affects drainage, maintenance requirements, walkability, and materials used. Having an idea of the pitch – but more specifically the slope – can help the homeowner make informed decisions regarding the amount of material needed and the type of roofing materials that will work best – and last the longest.

The primary purpose of a sloping roof is to redirect water and snow away – especially after torrential rain and heavy snowfall. The roof pitch prevents water from accumulating on the surface, therefore reducing the risk of damage – from mold to leaks, cracks, or the extreme case of a roof collapsing. In areas that are susceptible to a lot of rain and snow – particularly northern states – minimum pitch, or more commonly slope, levels are included in their building codes. And in these regions, the preference is to build homes with steeper roofs.

 

Roofing Factors/Aspects

As you get ready to build that dream home, give some thought to your roof choices, the pitch, and the impact on design and aesthetics. There are some factors to think through when it comes to the selection of steepness.

 

Climate

Consider the region and local weather. Again, if you live in an area with a lot of snow, rain, hail, and strong winds, a steeper roof can handle these elements much better than lower or medium-pitched ones.

 

Roofing materials are based on steepness and water penetration. For example, asphalt shingles are only suited for sloped surfaces because they allow water to penetrate the roof when installed on very shallow planes. In addition to asphalt shingles, high-pitched roofs can have wood shingles and slate tiles.

For roofs with a low pitch, choose roll or standing-seam metal roofing, and for flat roofs, choose tar and gravel or rubber membrane.

 

Maintenance

Another aspect to remember is maintenance. Every homeowner is aware that roofs require regular maintenance. The frequency, cost, and nature of maintenance requirements are all dependent on roof pitch/practices.

Once again, roofs with steeper pitches present few drainage problems. However, while tree leaves and other windblown debris accumulate on flat or low-sloped surfaces, shallow ones are easier to walk on during maintenance and repairs.

 

Attic Space

A pitched roof can increase square footage since it leaves room for an attic or a sleeping loft. Like the basement, the attic is used as extra storage space – and in similar ways, homeowners can be creative with it and design it as an extra bedroom, library, hangout/getaway space, playroom, and more.

If refurbishing the attic is not appealing, think about its other benefits – especially in regulating your home’s temperature. During the summer, attic insulation minimizes heat penetration from outside. In winter, attic insulation prevents heat from “escaping” the house.

 

Budget/Costs

Let’s talk about budgeting and related costs. Because a pitched roof covers more surface area, it requires more material – which means a higher budget and increased costs. Adding to the cost is the trickier design of a roof with a pitch – which raises labor and other professional roofer charges.

 

Other Factors

For rooftop installations like solar systems, roof gardens, and decks/outlooks, a flat or slightly pitched design is better. You can, of course, have these features – like solar systems – on a steep roof. But why sweat it when it is easier to install them on a flatter one?

 

Architectural Style and Curb Appeal

It is no secret that houses with steep roofs are more architecturally interesting, unique, and have tremendous curb appeal. Think Victorian, Arts and Crafts, Colonial, Cape Cod, European, French, Tudor, and Shingle Style. Most homeowners prefer the aesthetics of a gable, hip, or even gambrel roof – and like the idea of experimenting with several designs.

But there are others who may like the clean and minimalistic lines of contemporary urban buildings. For them, the flat-pitched roof is it. Ultimately, people choose what fits their lifestyles and needs – without losing sight of costs and other practical matters.

 

Types of roof pitches are grouped into three or four basic categories – from flat to low, moderate, and high slope.

• Flat roofs, while described as flat, are actually minimally pitched to allow water to drain. A flat roof generally ranges in slope from ½ in 12 to 1 or 2 in 12.

 

• Low-sloped roofs – those from 1/12 to 1/6 pitch (or a slope of 2 in 12 to 4 in 12) – are easy to walk on, thus making repairs and maintenance more efficient. But allowing the run-off of rain and snow is a bit more difficult to accomplish.

 

• Medium-sloped roofs have pitches of 1/4 (6:12 slope), which is the most common roof pitch. As with everything that is middle of the road. They provide a good balance between ease of access and water and snow runoff.

 

• Steep-sloped roofs are those designated with very highly angled pitches above 1/3 (generally slopes of 9:12, 10:12, and 12:12 or higher). Because of their angles, they are particularly challenging to walk on and may require extra fasteners.

 

Common Materials

Shingles and tiles are the popular selections for conventional and steep-pitched roofs (anywhere from 1/6 pitch, or 4:12 slope, and above). They are attractive and perform well.

• Asphalt shingles are economical, versatile, and work well on most residential roof pitches. They are easy to install, relatively long-lasting, and available in a variety of colors and styles.  Asphalt shingles are likely the most affordable roofing for moderate and steep-sloped roofs – between 50 cents and $1.50 per square foot.

• While clay tiles and manufactured slate are long-lasting, their disadvantage is their cost and weight. Prices run from $6 to $10 a square foot in most areas of the U.S. – with prices for real slate double these amounts.

• Concrete tiles can imitate both slate and clay and have prices similar to clay. Concrete, clay, and slate weigh between 900 to 1,200 pounds per square foot – so the roof deck supporting structure must be able to carry the additional weight.

• Metal can be used in any kind of roof pitch. The common material selections are painted or anodized aluminum and steel. Metal roofs have a long service life and weigh from 40 to 135 pounds 100 square feet, making them the lightest roofing products. Other advantages of metal include easy installation, low maintenance, lightweight, sustainability, and recyclability.

 

While roof pitch does not often figure in conversations about a new home, it is one of its most important structural elements. As you make plans to build your dream home, take the time to learn everything about pitch and slope to understand how it affects the roofing system, the safety – and the look of your home.

 

Footnote: The top left image title montage of this article is a 2,742-square-foot contemporary Farmhouse with four bedrooms and 3.5 baths. For details on the steeply-pitched-roof home with an open floor layout and split master bedroom design, go to Plan #142-1185.