How To Slope A Flat Roof

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

How to slope a flat roof.

Unlike sloped roofs flat roofs are susceptible to ponding water. The second is to slope the roof trusses themselves this is done by the truss manufacturer. This solution is perfect for homeowners looking for the easy option for adding slope to a flat roof property. Creating a positive slope roof is traditionally done by installing rigid board insulation such as xps or polyiso on flat or low sloped roofs.

However in some cases building owners hire contractors that poorly designed the roof. The slope of a roof or pitch is determined by how many inches the roof rises over 1 foot or 12 inches. There are two ways we typically use to create low slope on flat roofs. In general the minimum slope for a flat roof is 1 0 but as stated earlier this is only possible in theory.

There is a problem with using these materials though. Low slope roofs are from 0 to 3 12 in pitch. This means that the rise of the slope goes up or down 8 inches for every 12 inches. What is the most appropriate angle for flat roofing.

Xps and polyiso are available in boards that are no more than a few inches thick. Water that stays on a flat roof after it rains will weaken the material over time. The second is usually the easier and cheaper solution although the foam insulation adds some additional r value. Eventually water penetrates the building.

The first is using tapered foam insulation on top of the roof trusses. 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. Generally such roofs have a pitch ranging from 1 2 12 to 2 12. It takes the manufacturer s recommendations the unique conditions of the roof as well as the skills and the expertise of the installer to arrive at the right slope.

An example for a steep sloped roof is 8 12. If asphalt shingles are to be installed on a low slope roof special steps are required to avoid short roof life and roof leaks. Low pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. Notes to the table above.

Flat roofs should have a minimum slope to allow water to run off.