How To Slope A Flat Roof

To put it in perspective the angle of this slope would be around 30 degrees.

How to slope a flat roof.

In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory. This means that the rise of the slope goes up or down 8 inches for every 12 inches. However in some cases building owners hire contractors that poorly designed the roof. Normally 1 80 0 72 is the recommended minimum angle for a slope and this is universal across the vast majority of flat roofing systems regardless of the materials that they incorporate.

Creating a positive slope roof is traditionally done by installing rigid board insulation such as xps or polyiso on flat or low sloped roofs. Water that stays on a flat roof after it rains will weaken the material over time. The slope of a roof or pitch is determined by how many inches the roof rises over 1 foot or 12 inches. There is a problem with using these materials though.

Xps and polyiso are available in boards that are no more than a few inches thick. Notes to the table above. Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. Generally such roofs have a pitch ranging from 1 2 12 to 2 12.

What is the most appropriate angle for flat roofing. The first is using tapered foam insulation on top of the roof trusses. Flat roofs should have a minimum slope to allow water to run off. There are two ways we typically use to create low slope on flat roofs.

The second is to slope the roof trusses themselves this is done by the truss manufacturer. Some sources consider low slope to include 3 12 pitch roofs. Low slope roofs are from 0 to 3 12 in pitch. Eventually water penetrates the building.

Unlike sloped roofs flat roofs are susceptible to ponding water. Flat roofs which aren t perfectly flat require a small slope to allow for water runoff. This solution is perfect for homeowners looking for the easy option for adding slope to a flat roof property. The second is usually the easier and cheaper solution although the foam insulation adds some additional r value.

If asphalt shingles are to be installed on a low slope roof special steps are required to avoid short roof life and roof leaks.