Flat Roof Fall Ratio Calculator

The ratio is determined to be 1 in n which is different to the mathematical 1 n.

Flat roof fall ratio calculator.

Drag sliders to animate the results and diagram. Flat roof design guide. Common roof pitches and equivalent grade degree and radian angles. Learn more about finding the angle of a line using our slope calculator.

We can divide roofs into the following categories. According to bs 6229 bs 8217 flat roofs should be designed with minimum falls of 1 40 to ensure a finished fall of 1 80 can be achieved allowing for any inaccuracies in the construction. There are 4 different ways of that are used to specify the slope. This applies to general roof areas along with any internal gutters.

Take the roof s total square footage and divide by the total square footage handled by one drain. 6m 60 100mm difference between top and bottom. Flat roofs which aren t perfectly flat require a small slope to allow for water runoff. A pitch over 9 12 is considered a steep slope roof between 2 12 and 4 12 is considered a low slope roof and less than 2 12 is considered a flat roof.

50 000 4 400 11 36. Fall gradient x distance for example calculate the fall in a 50 metre section of foul water pipework if the gradient is to be 1 in 80. Generally such roofs have a pitch ranging from 1 2 12 to 2 12. The angle of inclination percentage per mille and it can also be expressed as a ratio.

The result is the number of drains needed. You can divide roofs into these categories. Enter run and known pitch angle or rise to calculate other dimensions enter run the flat level length then click pitch angle or rise to select then enter other known dimension angle or pitch. Roof pitch is often expressed as a ratio between rise and run in the form of x 12.

Most roof s have a pitch in the 4 12 to 9 12 range. A ratio of 1 1 62 is known as the golden ratio and therefore the vast majority of roof pitch in degrees charts you see will be working to this ratio at the very least. A gradient of 1 in 80 is converted to a number instead of a. The correct minimum fall of a flat roof should be 1 60 by design to acheive 1 80 with deflection ie sagging over time but with flat roofs with a gutter and no internal outlets to worry about over whelming the greater the fall the better.

The gradient calculator may be another online program that may interest you. Often you express roof pitch as the ratio between the rise and the run in the form of x 12. This is because steeper looks tend to fit more with the golden ratio which all architects work by. Or 12 drains required.