So it’s time for a new roof. Or perhaps you are planning a new home construction project and are considering what your new roof should look like. Surely, you have heard about all the exciting new roofing materials available today and are eager to get started. But, before you can make the call on what to put on the roof, you need to know the pitch or slope of the roof! 🙂
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Why It’s Important
The roof pitch is necessary for two things – one, estimating the amount of material to be ordered for the job and two, knowing what materials are suited for the roof. But, again we are jumping ahead of ourselves. Before we get started with all that we need to find out the pitch of a roof.
What is a roof pitch?
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Pitch, angle, incline, slope – they all can be used to refer to the steepness of a roof. In the roofing trade the go-to term is “pitch” and it is expressed in terms of “12 inches.” So the pitch of a roof is determined by how many inches the slope rises for every 12 inches it runs horizontally. If a roof increases in height by four inches for every foot of horizontal run, it is considered to have a “4-in-12 pitch” or just a “4 pitch.” Talk in terms of pitches and you will always be understood in the roofing universe. 😉
Measuring a roof pitch
Ideally you will have safe access to your roof from inside the building. If not you will need to make your measurement from on top of the roof itself or at the edge of the roof with a ladder. The tools required will be a contractor’s level at least 24 inches long and a tape measure. Place the butt end of the level against the edge of the roof and extend it into the air, balancing it until it becomes level. At that point measure down from the exposed butt end back to the roof surface. Divide the results by the number of 12-inch segments in your level. For example, if you used a 24-inch level and your measurement was 12 inches the pitch in your roof is 6-in-12.
You can also estimate a roof pitch by eyeballing it from the ground from the gable side with a level and ruler. If for some reason you have absolutely no access to basic tools you can guesstimate the pitch of a roof by knowing that clapboards generally present four inches of exposed face and a dollar bill is six inches. So you can count the clapboards from the low end of the roof to the peak and use a dollar bill to figure out your stride and pace off the the size of the building. Then make your mathematical calculations.
Using roof pitch to order materials
Once you know the width and length of the space to be covered you can apply the roof pitch to determine exactly how much roofing material to order without leaving yourself short or wasting money with overages. To do that requires basic geometry but fret not, you can just refer to tables that are standard in the industry:
Multipliers used for estimating roof area based on slope:
0 pitch and under – 1.00X the roof area (since this is a flat roof or nearly flat roof. You can go by the measurements taken by walking the roof)
1 pitch – 1.01
2 pitch – 1.02
3 pitch – 1.03
4 pitch – 1.05
5 pitch – 1.085
6 pitch – 1.12
7 pitch – 1.16
8 pitch – 1.21
9 pitch – 1.25
10 pitch – 1.31
11 pitch – 1.36
12 pitch – 1.42
Roof Pitch Expressed in Degrees:
12 pitch = 45 degrees
11 pitch = 42.5 degrees
10 pitch = 40 degrees
9 pitch = 37 degrees
8 pitch = 33.75 degrees
7 pitch = 30.5 degrees
6 pitch = 26.5 degrees
5 pitch = 22.5 degrees
4 pitch = 18.5 degrees
3 pitch = 14 degrees
2 pitch = 9.5 degrees
1 pitch = 4.5 degrees
0 pitch = 0 degrees
How Roof Pitch Manifests Itself in Various Roof Types
Roof shapes have evolved through history in different regions of the world from flat to steeply pitched. Here are some of the common shapes that top roofs today:
Flat roofs are common with industrial buildings boasting wide roof spans and are also popular in dry climates for houses where there is no need for the roof to help disperse rain and snow. Even in these arid regions so-called “flat roofs” are still installed with a slight pitch to keep water from pooling on top of the structure.
A mono-pitched roof runs from a taller wall to a wall of lesser height to produce a slope. This is often a configuration seen on simple shed buildings.
Saw-tooth roofs can often be seen on old-school factories that were constructed with a series of mono-pitched roofs that are used to allow sunlight to filter down to the shop floor.
Pent roof is a collection of low mono-pitched roofs often seen on residential terraces.
A gable roof is a traditional triangle-shaped roof that can range from a medium pitch to sharp angled roofs.
A-frame roof is the sharpest gable-style roof resembling the shape of the letter-A. It is a traditional roof shape employed everywhere from tropical huts to Nordic ski chalets.
Asian-style roofs: The influences of Asian architecture have infiltrated American shores in recent years. Gracefully sloping roofs are often of medium pitch which emphasize the horizontal spread of the buildings.
Hipped roofs: These distinctive roofs with overhanging eaves feature four medium pitched sides and are characteristic of Dutch architecture and help disperse snow loads in northern climates. Hipped roofs are often used in complex roof formations with the “hips” facing different directions.
Saltbox roofs: The workhorse of Colonial America, the familiar saltbox is a building that features a long, pitched roof on one side, similar to the lid on a salt storage box. Their attractiveness traces to the desire to make a two-story building function as a one-story building to reduce the tax bill. The large expanse of such a roof will cause greater expense to cover.
A mansard roof, in opposition to a salt box, offers the utility of a full half-room on the upper floor rather than an attic. It features tow pitches, one a shallow pitch atop a steeper slope.
Pyramidal roofs: Sometimes seen on square buildings, a tented or pyramidal roof, feature four slopes rising to a peak. These are often steeply pitched roofs.
Gambrel roofs: Popular with barns and other structures that create additional interior room, these stepped roofs feature a short steep, non-walkable slope before rising more gently to a ridge peak.
Clerestory roofs: Another popular form for factories requiring light infiltration, the clerestory features long, low-pitched roofs before the building rises to a traditional gabled section atop the structure.
Conical roofs: A staple of Queen Anne Victorian architecture these conical towers were topped with dunce-cap roofs that are too steep to be walked on.
Arched roofs: Seen on utility structures there are several types of medium-pitched roofs that feature curves from gentle arches to bows and barrels.
Circular roofs: These full arched roofs can be anything from domes to decorative Byzantine-inspired onion domes. Domed roofs can be low-pitched or fully circular.
Pros and cons of various roof slopes
Low pitch roofs are easier to install and safer to walk around to complete repairs and maintenance. This is fortunate since flat roofs are more prone to leaks and require frequent inspections. Low-pitch roofs are seldom used in regions of severe weather due to the stress of snow accumulation on roofs of structures. Flat roofs are significantly cheaper to install than a pitched roof but require more maintenance. Flat roofs are popular in regions of sparse rainfall and are favored by modern architects in contemporary designs.
Medium-pitched roofs come in a variety of styles and provide help with dispersing snow and rainfall while still being able to be inspected and repaired by the average homeowner by walking around the surface.
High-pitch, non-walkable roofs are dynamic and present an exciting appearance, but they are more expensive to install, and repairs will be left to roofing contractors with all the necessary safety equipment.
How roof pitch determines suitable roofing systems
Flat and nearly-flat roofs (a pitch of 1-in-12 or 2-in-12) cannot be covered with shingles or shakes of any material since there is not enough angle to combat the danger of blow-off. For that reason flat roofs are limited to these types of covering materials:
Tar and Gravel. Alternating levels of hot asphalt (tar) and heavy roofing felt finished with a gravel coating can be applied to a flat roof for protection. Typically between three and five layers are built up. The cost for this utilitarian roof covering lies mostly in the labor and will vary greatly depending on the location of the building. For a 2,000 square foot roof expect to pay around $2,500 for tools and supplies and upwards of $7,500 for labor. Built-up roofs are not a DIY project and will require professional installation; but the waterproofing for flat roofs can not be beat. A built-up roof can be expected to last 20 years.
Modified Bitumen. Historically, the word “bitumen” has been used interchangeably with asphalt and tar. It is a naturally-occurring goo that develops from millions of years of decomposing organic material and has been used since prehistoric times as a sealant. In modern roofing this bitumen has been infused into plies of polyester or fiberglass to create a weatherproofing roof material. The installation technique is similar to building up with tar and gravel but the plies are less expensive by half – about $1,250 for tools and supplies. Labor is a bit faster and expect a tab of about $6,500.
EPDM rubber. That is “ethylene propylene diene monomer” and it is the answer to the question, “what is a rubber roof?” Rubber is gaining in popularity for flat and low-slope roofs, even in residential applications. It is also a “built-up” roof but only requires a single ply, making it lighter and less stressful to the structure than an asphalt-based roof. It also does not require a gravel-covering to ward off harmful elements and UV rays from the sun. EPDM rubber roofs come in two options of thickness: 45 millimeters and 60 millimeters. As you can expect, materials are much more expensive and labor is less. The total cost for that 2,000 square foot EPDM roof will run between $10,000 and $13,000.
Roll Roofing. This quick and easy roofing solution consists of felt backing that is impregnated with asphalt and coated with minerals. It is the same material as asphalt shingles and is sold in rolls that will cover one square (100 square feet). You may hear it called “90-pound felt” because that is how much it weighs to pick up the roll. If you run into “15-pound felt” or “30-pound felt” that is underlayment material and too thin to be used as roof covering on its own. Roll roofing is what gives “tar-paper shacks” their name and is often avoided in residential roofing. Save it for sheds and chicken coops and other outbuildings. Roll roofing will cost about half of what a shingled roof will cost and can be installed as a DIY project, but do not expect this roofing material to last much beyond 10 years. A roll of 90-pound felt will cost in the neighborhood of $50.
Metal Roofing. Metal should never be set up on a completely flat roof since they were not designed to handle pooling water which will lead to premature rusting and deterioration. Standing seam metal roofs with mechanical lock systems to ward off leaks can be successfully and attractively installed on roofs with at least a slope of 1-in-12. Metal panels install quickly and easily, and can be done without professional assistance, especially on low slope roofs, and come in a much wider range of colors than other nearly-flat roofing options. Expect to pay around $10 to $12 per square foot for a standing seam metal roof, installed. If you are considering a DIY route, you can have pre-cut standing seam panels delivered to your site at a cost of about $5.00 per square foot.
No, you cannot install Metal Shingles on a low-slope roof
For budget conscious building owners, metal shingles will run about $7 to $10 per square foot, installed, while corrugated metal sheets can be installed for $3.50 to $5.50 per square foot for materials and labor. Keep in mind that neither metal shingles not corrugated metal panels are suitable options for low-slope or nearly flat roofs. A minimum pitch of 3-in-12 will be required.
Suitable Materials for Pitched Roofs
Pitched roofs begin with with slopes greater than 3-in-12. The 45-degree roofs seen on A-frame houses are 12-in-12 but roofs can be even steeper – consider the mansard roofs introduced by French Second Empire architects in the middle of the 1800s. These roofs with nearly vertical faces can boast a pitch of 20-in-12. Pitched roofs not only introduce greater degrees of installation difficulty into the cost structure, but they also permit the complicated roof complexes on some residences.
Pitched roofs are most often the provence of shingles, although standing seam roofs are becoming ever more popular on pitched roofs as well. Shingles can be fabricated from a wide range of materials such as asphalt (least expensive) to natural wood, metal, tiles and heavy slate (most expensive). Exact costs will vary depending on aesthetic choices and the vagaries of installation but expect a 2,000 square foot roof clad in asphalt shingles to run around $7,500 dollars and be prepared to pay between $25,000 and $35,000 for a natural slate covering.
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The variety of roofing shingles allows for a rainbow of colors and varying shapes and sizes. Installation techniques can add distinctive lines and patterns to the look of a roof. Shingled roofs will last 15 to 30 years for asphalt or wood, to generations for metal, tiles and slate.
Investigate fire ratings for various materials suitable for pitched roofs, in accordance with local building codes before proceeding.
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