Roof Pitch Factor Chart

The pitch of the roof is the measure of its steepness. The pitch of the roof has a great role in determining:

  • Cost of the roof
  • Type of roofing materials to be used
  • Quantum of roofing material to be used

The measurement of roof pitch is thus important. The steeper the pitch of the roof, the higher the cost. It is thus necessary to figure out the pitch of the roof correctly. If the roof has more than one pitch then squares per roof should be calculated differently for every measure of steepness using the roof pitch factor chart.

Roof Pitch Angle Roof Pitch Factor Valley & Hip Factor
1/12 4.76° 1.0035 1.4167
2/12 9.46° 1.0138 1.4240
3/12 14.04° 1.0308 1.4362
4/12 18.43° 1.0541 1.4530
5/12 22.62° 1.0833 1.4743
6/12 26.57° 1.1180 1.5000
7/12 30.26° 1.1577 1.5298
8/12 33.69° 1.2019 1.5635
9/12 36.37° 1.2500 1.6008
10/12 39.81° 1.3017 1.6415
11/12 42.51° 1.3566 1.6853
12/12 45.00° 1.4142 1.7320

HOW TO DETERMINE ROOF PITCH

As the relevance of pitch of roof is now understood, it is worthy to understand how pitch of the roof is calculated. The things which you may need are an extension ladder, a level, a ruler, and a person to assist. If the roof is too steep and slippery then you can take the help of a professional to do this task. Here are the steps to assist you so that you can do it all by yourself:

Step 1: Take a ladder and reach to the top of the roof. You can tie the ladder to the gutter or the fascia board. The roof may be slippery, as it is generally slanting and therefore you should be a little cautious.

Step 2: Place the level at the center of the top ridge. From here note down the reading of the level to the bottom of the roof. The scale with which you are measuring should have 12 runs or spans. These runs or spans indicate the inches. This measurement is for a plain roof.

Step 3: However, if the roof has thick layers that protrude over the roof then you need to add for that as well. You can do this by putting the tape at the bottom of the layer and extending it to the upper part of the roof sheet. It may hardly be 1 or 2 inches, depending upon the height of the roof tiles.

Step 4: For instance, if on an earlier measurement the tape measured 8”, then it means that the roof pitch is 8/12; if the layers of the roof protrude above the roof by 1” then the total pitch of your roof would be 9/12, i.e., (8+1).

Step 5: Now you are finished with the difficult part of measuring the pitch of the roof. The leftover part is very simple, as it simply involves mathematics. From the roof pitch factor table, note down the roof pitch conversion factor corresponding to the roof pitch calculated. In our example, the roof pitch was calculated as 9/12, which has a factor of 1.25 in the table.

Step 6: The last step is to come off the ladder and simply multiply the factor determined in the step above with the number of total squares of the area. If the area is 10,000 squares then roof pitch would be 12,500 (10,000x1.25).

The roof pitch can also be determined by staying on the ground. This is done by measuring the width of the roof on the gable side and the exterior wall sections from corner to corner. The overhanging portions on the roof are duly added into the figure.

SLOPE OF THE ROOF

To measure the roof you need to have knowledge of geometry as well! Seems odd but, yes, it’s true! You need not have high-class knowledge but just some basic knowledge. Consider the roof as if two identical triangles are attached back to back. If you know the base of the triangle then you can calculate the length of the long base of the triangle using trigonometry or Pythagoras theorem. Slope is the vertical rise per foot of the horizontal run and the slope is measured by this technique. Slope and pitch are often used as the same terms but they have a slight difference. Pitch is the vertical rise in the roof, which is divided by the horizontal span. Thus both the terms are different. The roof slope factor chart also consists of conversion factors to determine the slope of the roof. The headache of using Pythagoras and trigonometry can be spared by making use of these charts. A 10” slope roof should not be confused with a 10” pitch roof, as a 10” slope roof means that the roof rises by ten inches for every foot of run. This roof slope factor table also consists of hip and valley factors to measure the possible hips and valleys.

LENGTH OF THE RAFTER

This way, the pitch of the roof and the slope of the roof can be measured. The higher the slope the steeper it is. The length of the rafters can also be determined while determining the slope. A valley, or hip, rafter is generally required at the area where two roof lines meet. To judge the length of this rafter placed at the joint of the roofs, you have to multiply the length of the normal rafter by 1.5. This means if at the time of making the roof you used the rafter which was 5” in length then you can multiply it by 1.5 to determine 7.5”, which represents the length of the rafter between two roofs.

ANGLES AND GRADES

The roof pitch is described as Rise in Run, which is 12 units. The whole table of roof pitch and slope gives a conversion factor so as to obtain a numerical figure of the slope. This numerical figure is significant, as not everybody can understand the technical measurements. One medium to describe the roof pitch is in 12 runs. For example, if the pitch of the roof is 6” then it is written as 6/12. This 6/12 roof pitch factor can also be described in other measures. The angle for 6/12 is 26.57° and in grades it is described as 50%. Grades are the measure of percentage. As 6 is half of 12, it is considered to be 50%. Similarly, grades and angles can be calculated for the actual pitch using the roof pitch factor formula. If the house is irregular in shape then you can calculate the slope by measuring the parts separately and then aggregating them all.