Flat Roof Fall Ratio Calculator

This applies to general roof areas along with any internal gutters.

Flat roof fall ratio calculator. 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. 6m 60 100mm difference between top and bottom. 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. Take the roof s total square footage and divide by the total square footage handled by one drain.

We can divide roofs into the following categories. 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. For example a pitch 1 12 means that per every twelve yards of building length the rise will be equal to one yard. Drag sliders to animate the results and diagram.

The result is the number of drains needed. 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. Most roof s have a pitch in the 4 12 to 9 12 range. Roof pitch is often expressed as a ratio between rise and run in the form of x 12.

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 roofs which aren t perfectly flat require a small slope to allow for water runoff. 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.

Flat roof design guide. 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. There are 4 different ways of that are used to specify the slope. Or 12 drains required.

Common roof pitches and equivalent grade degree and radian angles. Generally such roofs have a pitch ranging from 1 2 12 to 2 12. The triangle diagram will be re drawn to scale with all dimensions marked. The angle of inclination percentage per mille and it can also be expressed as a ratio.

A gradient of 1 in 80 is converted to a number instead of a. The gradient calculator may be another online program that may interest you. 50 000 4 400 11 36. Flat roofs are not perfectly flat in reality they need a small slope for water runoff.