Minimum Roof Pitch For Snow Loads

The standing seam metal roof on this ice hockey rink leaked like a sieve a few weeks after the first snow arrived.

Minimum roof pitch for snow loads.

For example a roof with a 6 inch 12 pitch is one where it rises 6 inches vertically for every 12 inches of the horizontal run. If your roof is 1 000 square feet the total snow load is 15 000 pounds of snow. Per local ordinance it is 20 psf with further statement that snow loads shall be determined per section 7 of asce 7 but the design roof load shall not be less than a uniform snow load of 25 psf. There are some standing seam metal roofing options available from atas and other manufacturers that can be installed on a roof with pitch of 1 12.

Flat roof snow loads p f the snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load. This can be accomplished by measuring the number of inches the roof rises vertically for every 12 inches it extends horizontally. The minimum roof slope allowed by code for any type of roof is in 12 applicable only to coal tar pitch roof systems. You could also opt for a pvc flat roofing membrane.

A minimum slope of 1 inch per foot is recommended in snow country. To figure out the load on your roof take the depth of snow in feet and multiply it by the weight of a cubic foot of snow. 90 mph for both 2003 irc and 2003 ibc. The chief reason for having a roof pitch is to redirect water and snow away from the roof and avoid any percolation that might result from stagnation of water on the roof.

If you live in the us our snow load calculator compares the total weight on your roof with the permissible load calculated according to the standards issued by the american society of civil engineers regarding the minimum design loads for buildings and other structures asce7 16. Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10. So you would need to pick the right option as most regular standing seam metal roofs will require a roof pitch of 2 12 or even 3 12 at a minimum. In our case let s assume that our structure has a flat roof roof slope 5.

In general determining the pitch of an existing roof is a simple calculation. The following table provides the minimum required allowable roof slope for each type of roofing material mentioned in the code. Per 2003 irc and 2003 ibc. The 1 4 inch per foot slope was not adequate.