Flat Roof Fall Ratio Calculator

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.

Flat roof fall ratio calculator.

Take the roof s total square footage and divide by the total square footage handled by one drain. 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. Or 12 drains required. 6m 60 100mm difference between top and bottom.

Flat roof design guide. There are 4 different ways of that are used to specify the slope. A gradient of 1 in 80 is converted to a number instead of a. Drag sliders to animate the results and diagram.

The angle of inclination percentage per mille and it can also be expressed as a ratio. Roof pitch is often expressed as a ratio between rise and run in the form of x 12. 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. The result is the number of drains needed.

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. Most roof s have a pitch in the 4 12 to 9 12 range. 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. Flat roofs are not perfectly flat in reality they need a small slope for water runoff.

You can divide roofs into these categories. We can divide roofs into the following categories. The ratio is determined to be 1 in n which is different to the mathematical 1 n. For example a pitch 1 12 means that per every twelve yards of building length the rise will be equal to one yard.

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. This applies to general roof areas along with any internal gutters. This is because steeper looks tend to fit more with the golden ratio which all architects work by. 50 000 4 400 11 36.

The gradient calculator may be another online program that may interest you. Learn more about finding the angle of a line using our slope calculator. Flat roofs which aren t perfectly flat require a small slope to allow for water runoff. Generally such roofs have a pitch ranging from 1 2 12 to 2 12.