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DIY Roofing Calculator - How do you calculate the roof area?

Use the Homesteady DIY Roofing Calculator to determine the rafter length and roof pitch for your construction project. Provide a few specifications and let the calculator do the rest!

How to use Homesteady DIY Roofing Calculator

1. Height of Rise

The first step to any roofing project is determining the ​height of the rise​. The height of the rise is the vertical distance from the base of the roof to its uppermost point (where the rafters meet). The rise is always measured at a 90deg angle from the base of the roof.

2. Length of Run

The run is the distance from the bottom point of the rise to the edge of roof's base. The run is measured at a 180deg angle.

With the height of the rise and length of the run, the roof calculator will determine the length of rafters for your roof, as well as the pitch.

The pitch is the slope created by the rafter. Pitch is calculated using the same formula that describes a right triangle, also known as the Pythagorean theorem. Pitch is commonly expressed as a ratio between rise and run in the form of x:12, where x represents the rise (in ft) for every 12 feet of building length.

Typically, roofs with higher pitches are better suited for climates with lots of rain and snow.

In general, there are 4 types of roofs. They can be classified as flat roofs, which have a small slope under 17%, low pitched roofs, which have a slope under 33%, conventional roofs, which have a slope ranging from 33% to 75%, and high-pitched roofs, which have a slop up to 175%.

The four types of roofs:

  • Flat roofs -​ small sloop under 17%
  • Low pitched roofs​ - slope under 33%
  • Conventional roofs​ - slope between 33% and 75%
  • High-pitched roofs​ - slope up to 175%

How the Roofing Calculator works

All measurements should be converted to feet

Rafter length​ = rafter^2 = rise^2 + run^2

Roof pitch (percentage)​ = (rise / run) * 100

Roof pitch (degree)​ = arctan(rise / run) * (180 / pi)

Roof pitch (x:12)​ = (12 * rise) / run

Standard Slopes of a Roof

Important Tips

  • Check local permit laws and building codes before doing any type of construction.
  • The slope of the roof will directly influence the cost of building and maintenance associated with your home.

For example, a roof with a low slope may not allow water to run off effectively, causing pooling and eventually leaking.

Alternatively, a roof with a high or steep slope will probably require specialized equipment in order to work on it.

Either will translate into higher costs for both initial construction and regular maintenance down the road.

Designing your home?

If you are designing a home and trying to determine what slope to design the roof, there are several factors to consider:

  1. The slope of your home affects its aesthetics.
  2. It is also important to think about the weather conditions. For cold, snowy climates, you will want to choose a steep roof pitch.
  3. Certain materials are only available for certain roof slopes. For example, asphalt shingles should never be used for a low pitched roof.

Styles of Roofs

The slope of a roof is ​dependent upon the style of the roof​ itself. In the U.S., roofs are most often constructed as gable, hip or Mansard.

  • A gable roof​ is a symmetrical roof that looks like an upturned, open book lying atop the frame of the house. Gable roofs can be any slope but are common in the 3-12 category.
  • Hip roofs​ are low- to high-sloped roofs that are shaped like a trapezoid pyramid with four connecting points on each corner that meet at the top, or the ridge of the house.
  • A Mansard roof​, which is found on more traditionally styled homes, is a hip roof with extremely sloped sides that rise to meet a flat roof.

Builders in North America describe the slope of a roof as a ratio:

The types of roofs:

  • Low pitched roofs​ - pitch lower than 3/12
  • Conventional roofs​ - pitch between 4/12 to 6/12
  • High-pitched roofs​ - pitch higher than 7/12