Flat Roof Fall Ratio Calculator

Flat roof design guide.

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. 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. For example a pitch 1 12 means that per every twelve yards of building length the rise will be equal to one yard. Firrings it is normal practice for the joists of a flat roof to be set level thus creating a perfectly level ceiling.

This applies to general roof areas along with any internal gutters. We can divide roofs into the following categories. 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. Roof pitch is often expressed as a ratio between rise and run in the form of x 12.

Flat roofs are not perfectly flat in reality they need a small slope for water runoff. Visit this page using a phone or tablet to directly measure pitch and angles. The gradient calculator may be another online program that may interest you. The angle of inclination percentage per mille and it can also be expressed as a ratio.

The following tools estimate the area of a roof as well as the amount of materials necessary to construct a roof of a given area. The house base area is the area of land that the house covers and for more complex shapes can be estimated using the area calculator. 6m 60 100mm difference between top and bottom. Often you express roof pitch as the ratio between the rise and the run in the form of x 12.

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. Common roof pitches and equivalent grade degree and radian angles. 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.

Drag sliders to animate the results and diagram. The ratio is determined to be 1 in n which is different to the mathematical 1 n. The fall of the roof may be created in the structure itself by laying the supporting beams or joists at a slope giving a sloping soffit or by installing tapered beams with horizontal soffits. Most roof s have a pitch in the 4 12 to 9 12 range.

You can divide roofs into these categories. 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.