How do you calculate the rise and run of a roof?

Asked by: James Maza

If you know the roof’s angle in degrees, you can find the roof pitch by converting the angle in degrees to a slope, then finding the rise by multiplying the slope by 12. First, find the slope by finding the tangent of the degrees, e.g. slope = tan(degrees). Then multiply the slope by 12 to get the rise.

How do you find the rise and run of a roof?

So six six over twelve rise over run equals. And you want to figure out your rise. So we'll put that as X and your run is two feet then you just cross multiply. And divide to answer for X.

How do you measure the rise of a roof?

Place the end of the level against the bottom edge of a roof rafter and hold it perfectly level. Measure from the 12-inch mark on the level vertically to the bottom edge of the rafter. That measurement is the number of inches that the roof rises in 12 inches.

What is the rise and run of a roof?

Roof pitch or slope is the angle of the roof surface above the “flat” or horizontal plane. Roofers express roof slope as “rise” or “pitch”, measured in inches of vertical rise per foot of horizontal distance or “run”.

How do I calculate rafter rise?

Determine the Square Footage Factor



If the slope (rise and run) is 4/12, then you multiply your square footage by 1.06. If the slope (rise and run) is 5/12, then you multiply your square footage by 1.08. If the slope (rise and run) is 6/12, then you multiply your square footage by 1.12.

What is the standard slope of a roof?

The most commonly used roof pitches fall in a range between 4/12 and 9/12. Pitches lower than 4/12 have a slight angle, and they are defined as low-slope roofs. Pitches of less than 2/12 are considered flat roofs, even though they may be very slightly angled.

What roof pitch is 20 degrees?

Table 2: Slopes in Degrees Converted to Standard Roof Pitch

How is roof pitch calculated?

And all you need to do is find the 12 inch mark on your square. Line that up with your roof. Get your level on make sure that your level.

How do you calculate a 2% slope?

To calculate percent slope, divide the difference between the elevations of two points by the distance between them, then multiply the quotient by 100. The difference in elevation between points is called the rise. The distance between the points is called the run. Thus, percent slope equals (rise / run) x 100.

How do you figure roof rafters?

The first thing to do when working out the actual length of a common rafter is determine the horizontal span of the rafter as discussed in the previous page. Each common rafter span is calculated by subtracting the thickness of the ridge from the total span, then dividing the answer by two.

How do you calculate rafter slope?

Or you can take a tape measure. Just one hand now the winds picked up but you take a tape measure. Measure up on the outside of that mark. See yeah well you have my regular camera. Here.

What size rafters do I need for a 20 foot span?

As per general rules and guideline, for 10 -12 foot span, generally you need 2″×6″ size of rafter, for 15 -16 foot span, you need 2″×8″ rafter, for 18 – 20 foot span, you need 2″×10″ rafter & for 24 foot span, you need 2″×6″ size of rafter placed at 16″ apart from centre.

How far can a 2×6 rafter span without support?

A 2×6 rafter can span 14 feet 8 inches when spaced 16 inches apart with No. 1-grade southern pine lumber on a roof with a 3/12 slope or less with a maximum live load of 20 pounds per square foot and a dead load of 15 psf.

Can I use 2×6 for rafters?

You can use either 2×6 or 2×4 rafters for roofs with a 3/12 pitch or greater, but it depends on the overall size of your shed. For roofs that won’t experience heavy snow loads, a gable roof can span up to 22′ with 2×4 rafters.