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Roof slope calculation in construction

Roof slope calculation in the construction

When you’re deciding on a metal roof for your new home or re-roofing project, knowing your roof slope is important. Roof slope helps you determine what type of metal panel may be best for your home, as well affects how the system will be installed. It also matters in terms of a home or building’s integrity and safety.

Roof slope calculation is commonly defined by the rise-over-run ratio. If a roof slope “rises”, say, 4 inches when measured 12 inches along the bottom of a horizontal roof truss, the roof slope is said to be 4:12; i.e., 4 inches of rise per 12 inches (one foot) of run

Roof Slope  

Roof slope is the incline of the roof. It is expressed as a ratio of vertical rise to horizontal run, and tells you how many inches the roof rises for every twelve inches in depth. The higher the rise, the steeper the roof is. The measurement ratio is always expressed as inches per foot. For example, a roof that rises six inches for every foot, it would be written as 4:12. Typically, the most common roof slopes will be referred to as flat, low-slope, medium-slope, and steep-slope.

roof slope calculation

Why is Roof Slope Important?

Knowing your roof’s slope is key in installing a new roof or replacing an old one. There are quite a few reasons why this component is important to the entire roofing system, including the following:

  • Determines Materials— The steepness of your roof can be a determining factor in which type of metal roofing materials you can or cannot use. Under all of Bridger Steel’s metal roofing panels, you will find a drop-down menu under “Product Details” that shows “Recommended Roof Slope.” Knowing what your slope is can help you narrow down the choices and ensure you’re getting the best product for your roof.
  • Protects Against Elements — The slope of a roof is also important because it helps to protect your home against harsh weather, allows for rain and snow run-off, and prevents moisture pooling. Therefore, your roof is protected from water and mold damage.
  • Protects Against Collapses — Especially in environments with heavy snowfall, having the proper roof slope helps protect your home against roof collapses. Many states have building codes that include a minimum pitch requirement in order to protect homeowners against roof collapse.

How to make Roof Slope calculation.

In order to measure your roof slope, you’ll need a level and tape measure. You’ll want to first measure 12 inches from one end of your level and mark it. While you can measure a roof from the outside surface area, the most accurate way to find your slope is from inside an unfinished attic using the rafters.

First, you’ll want to place your level against the bottom of the rafter board. Next, measure vertically from the 12 inch mark on your level to the bottom edge of the rafter. Then, this will give you your rise over run.

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