Flat Roof Snow

Excessive rain heavy snow and built up ice all pose extra challenges for flat roofed homes.

Flat roof snow.

This down bearing pressure can cause the roof to bow and result in ponding under the roof structure. You need to use a snow load formula for flat roofs. Without that space heat inside your house can warm up your roof melting any snow that s piled up. Another is that they cannot handle as much snow weight as pitched roofs because the snow sits directly on the roof.

One of them is that flat roofs leak more easily than pitched ones. Snow and your flat roof there are a few common misconceptions regarding flat roofs that are stubbornly persistent. When water from that melted snow works its way to the edges of your roof where it isn t as warm and then re freezes it can also form ice dams. In our case let s assume that our structure has a flat roof roof slope 5.

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. With a flat roof you don t have the typical attic space afforded by a sloped roof. As snow falls it can accumulate on your flat roof putting unnecessary weight on the structure. The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load.

And whenever it snows the flat roof supports an additional insulating blanket. 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. The flat roof snow load is calculated using formula 7 3 1. Since snow falls at slow steady speeds large quantities of snow can fall on the roof resulting in bowing.

First figure out how deep the snow is piled up there. 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. The r value or resistance to heat flow for snow is about r 1 per inch. 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. 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.