# Roof Pitch Factors

It is very important to determine the roof pitch factors for designing the roof. The roof pitch affects all the other areas in the estimate. The steeper your roof pitch, heavier it is to your pockets. This article will help you calculate the roof pitch factors.

DecorDezine Staff

Last Updated: Jan 19, 2018

There are many ways to determine roof pitch and the best way to calculate roof pitch accurately is to give the range at which the roof surface will make a horizontal plane. Thus, thirty degrees, forty-five degrees or sixty degrees, help make a building roof pitch that is in a horizontal plane. This system is used by civil engineers mostly and carpenters and architects use a different system generally.

Determining Roof Pitch Factors

To find the roof pitch you need to place a level across the top ridge with a 12" mark that rests directly above the center top of the ridge. Be sure to level the level. Take measurements from the surface of the roof to the bottom of the level. The inches that you get as reading is nothing but your roof pitch. For example, when your tape reads 7" it means the roof pitch is 7/12. If there are existing roof layers, then determine roof pitch by the thickness of these layers of roof that protrude above the roof sheathing. Add this amount to the tape measurement reading. For example, the roof layer that protrudes above the roof is 1", so add 1" to your tape reading. That is, if your tape reads 7" then add 1", that will give you 8/12. Then multiply the square footage with the roof pitch factor to get the total area of the roof.

If you do not wish to climb on the roof to calculate roof pitch, then use a ladder. You can calculate roof pitch from the rafter tail bottom or at a barge rafter at the gable end on the roof over hangs. The procedure to follow is the same. This gives a more accurate reading as the layer of roofing does not need to be compensated.

Roof Pitch Formula

The roof pitch formula is as follows:

- Place a level against a roof.
- The point where the level touches the roof, measure 12" that is called the run.
- Then, from this point down the roof, measure the distance in inches. The number obtained is called the rise.
- Thus, the roof pitch factor will be expressed as rise over run, that is 7/12.

Roof Pitch Factor Chart

Roof Pitch |
Roof Pitch Slope Factor |
Valley and Hip Factor |

1:12 | 1.0035 | 1.4167 |

2:12 | 1.0138 | 1.4240 |

3:12 | 1.0308 | 1.4362 |

4:12 | 1.0541 | 1.4530 |

5:12 | 1.0833 | 1.4743 |

6:12 | 1.1180 | 1.5000 |

7:12 | 1.1577 | 1.5298 |

8:12 | 1.2019 | 1.5635 |

9:12 | 1.2500 | 1.6008 |

10:12 | 1.3017 | 1.6415 |

11:12 | 1.3566 | 1.6853 |

12:12 | 1.4142 | 1.7320 |

Types of Pitched Roofs

Low Pitched Roof

The pitch that is below 3 1/2 is called low pitched roof. These are very easy to build. However, one should not use asphalt shingles for these roofs. You need special roofing materials for these roofs. These low pitched roofs are cheaper to build but require regular maintenance.

Medium Pitched Roof

The pitch that lies between the range of 3 1/2 and 7 1/2 is called medium pitched roofs. These are the most commonly observed pitched roofs in the United States. One can walk over these roofs safely without any use of special climbing equipment. These roofs are used for sheds, garages, etc.

Steep Pitched Roof

Pitches that go beyond 7 1/2 are steep pitched roofs. One requires special climbing equipment and safety gear to walk over these roofs. These roofs are expensive and will last longer than low pitched roofs.