Some Roofs start collapsing at around 3 to 5 feet of snow load

 While I was staying at Timberline Lodge (about 65 miles from Portland on Mt. Hood) a few years ago the Building next door where people rent skis and snowboards has a relatively flat roof for some reason. I spoke with one of the men clearing off the snow with a snow shovel and he told me that they have to get the snow off a roof like this before it goes above about 3 feet of snow to prevent roof collapse. At the time the snow was approaching 4 to 5 feet deep on this roof.

The best way to avoid a collapsed roof from snow where very much falls at one time is to have a very steep roof like you see on an A-Frame. It's one way to avoid shoveling snow or a collapsing roof worldwide in places where you can get over 3 to 5 feet of snow at one time on the ground.

A friend of mine originally built himself an A-Frame on his land and then later jacked up his A-Frame and built a regular house on the first floor. this way he had all the advantages of the A-Frame and all the room of a regular house on the first floor. So he NEVER has to shovel snow off his roof.

The last time I talked to him there was 10 to 12 feet of snow on the ground. Likely he now has 15 to 20 feet of snow there at this time. However, with a snow blower he has kept his road open across his 2 1/2 acres to the nearest road which is plowed by the County. But, when you look out of a home like this in this much snow is all you can see is snow and that's all. This is in the Mt. Shasta area at around 4000 feet which gets more snow in the McCloud area than Mt. Shasta city does (for whatever the reason). Mt. Shasta city is at around 3500 to 3700 feet in elevation for a comparison.

A friend of mine in Mt. Shasta City says he has 3 feet of snow on the ground on his acreage and has to walk through several acres of snow to get to his car which he parked on the nearest paved and plowed road.

Also, the 3 to 5 feet also depends upon how dense the snow is. For example, if it is powder snow it is very light but wet snow is very heavy and dense and collapses roofs right and left if over 3 to 5 feet deep. It's also true that flat roofs will collapse quicker especially big flat roofs like supermarkets often have. They just don't usually have enough pitch to shed snow.