Flat Roof Snow

For roofs that are flat and with ground snow loads lower than 20 pounds per square foot the roof snow load is equal to 70 of the product of the exposure thermal and importance factors and the ground snow load.

Flat roof snow.

Snow and your flat roof there are a few common misconceptions regarding flat roofs that are stubbornly persistent. Radiant tubing technology just can t get enough energy to the surface to effectively melt snow. With a flat roof you don t have the typical attic space afforded by a sloped roof. Without that space heat inside your house can warm up your roof melting any snow that s piled up.

You need to use a snow load formula for flat roofs. Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10. If your roof is flat it is more likely to have snow load problems than if it is pitched. The flat roof snow load is calculated using formula 7 3 1.

That means 12 inches of snow on a flat roof creates an additional r 12 of insulation that arrives at a time of year when you most need it. While not frequent per se the low slope of a flat roof does make it more prone to certain problems particularly when it interacts with the elements. The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load. Another is that they cannot handle as much snow weight as pitched roofs because the snow sits directly on the roof.

First figure out how deep the snow is piled up there. Since snow falls at slow steady speeds large quantities of snow can fall on the roof resulting in bowing. Excessive rain heavy snow and built up ice all pose extra challenges for flat roofed homes. One of them is that flat roofs leak more easily than pitched ones.

And whenever it snows the flat roof supports an additional insulating blanket. The r value or resistance to heat flow for snow is about r 1 per inch. The easiest way is to push a yardstick into the snow on the roof selecting an area that looks typical of the overall snow depth. Snow melting flat roofs requires high output over a large surface area due to the heat transfer properties of gravel.

As snow falls it can accumulate on your flat roof putting unnecessary weight on the structure. In our case let s assume that our structure has a flat roof roof slope 5.