Alpo Posted June 18, 2020 Share Posted June 18, 2020 Based on TV and movies, it appears to me that most tall apartment buildings in northern cities have flat roofs. Your basic single-family dwelling has a steeply pitched roof, so that cold wet white stuff, that falls out of the sky during the winter, will not pile up on the roof and either crush it from the weight or rot it from the moisture. Yet a 20-story apartment building will have a flat roof. I'm sure that the roof would be concrete, instead of 2x6s and 3/4 inch plywood, so moisture most likely would not be a problem. But there is the weight of the snow. Without gravity pulling it down the steep sides of a sharply pitched roof, it seems like it would just pile up and get deeper and deeper and deeper. Two, six, fourteen feet? Doesn't it? Link to comment Share on other sites More sharing options...
Dusty Boots Posted June 18, 2020 Share Posted June 18, 2020 49 minutes ago, Alpo said: Based on TV and movies, it appears to me that most tall apartment buildings in northern cities have flat roofs. Your basic single-family dwelling has a steeply pitched roof, so that cold wet white stuff, that falls out of the sky during the winter, will not pile up on the roof and either crush it from the weight or rot it from the moisture. Yet a 20-story apartment building will have a flat roof. I'm sure that the roof would be concrete, instead of 2x6s and 3/4 inch plywood, so moisture most likely would not be a problem. But there is the weight of the snow. Without gravity pulling it down the steep sides of a sharply pitched roof, it seems like it would just pile up and get deeper and deeper and deeper. Two, six, fourteen feet? Doesn't it? Would hate to be hit by a large snow drift falling from a 20 story building. Link to comment Share on other sites More sharing options...
Wild Will Bartell Posted June 18, 2020 Share Posted June 18, 2020 The way I remember it, the flat roof was covered with long strips of an asphalt shingle-type material held together with tar. In the summer, the soles of your boots would stick to it a bit while walking/running. Never went up there during the winter. Also not sure if it was concrete or another material underneath. The perimeter of the roof had a 2-3’ high cinder block crown with drainage slots at roof level every few feet so the rain and melting snow could drain down the sides of the building. I haven’t been up on top of those types of buildings in many, many years so I don’t know what they’re like nowadays. Link to comment Share on other sites More sharing options...
Assassin Posted June 18, 2020 Share Posted June 18, 2020 Mechanical systems are roof mounted on taller buildings, along with elevator tower/room. Flat roofs are sloped towards internal drains, the heat escaping from inside the building and the sun keep the snow and ice melted. 3-4 story buildings or less will have scuppers for water to drain to the outside of the building. Typically, bar joists span the roof, then sheets of ribbed steel are placed over the joists, metal sheets are puddle welded to the joists. Then, insulated panels are laid over steel, Those insulated panels are covered with rubber membrane, or EPDM roof material. Now most roofing is a lighter color so the building doesn't absorb heat. Some flat roofs are covered with spray foam or "handyman in a can" type of rubber sealant. No where you want to be on a hot summer day. They haven't installed tar roofs for many years, there is no warranty on built up roofs anymore. Link to comment Share on other sites More sharing options...
Sedalia Dave Posted June 18, 2020 Share Posted June 18, 2020 Why all buildings over 1 story should all be flat Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted June 18, 2020 Share Posted June 18, 2020 My grandparents had a Victorian built before 1900 with a slate roof. When the snow falls off it all falls off. Amazing that no one ever got killed. Link to comment Share on other sites More sharing options...
Dustin Checotah Posted June 19, 2020 Share Posted June 19, 2020 Hey Alpo I worked in not a tall building that had a footprint of about 150,000 square feet. It was also a flat roof. During one or our bad winter storms we had ice and snow on it enough to cause the EMT (electrical metal tubing to flex where it came down from the ceiling. I went up on the roof and measured the snow in a few places to get an estimate of what was there. I figured with the weight of the snow and ice we had 13.5 million pounds of snow load on the roof. Luckily it melted in about 3 days. You could hear the water running through the drains. Link to comment Share on other sites More sharing options...
Marshal Mo Hare, SASS #45984 Posted June 19, 2020 Share Posted June 19, 2020 Where you said “two, six, fourteen feet”... you should know that snow does not pile up like that. If we have a blizzard that drops 30”, for example, the weather service has a way of measuring snowfall before it has a chance to melt or compress. It Soon starts to compress and melt. Rarely, like every ten to fifteen years does total snow depth get to three feet. snow banks, however, but they are not on roofs. Link to comment Share on other sites More sharing options...
Alpo Posted June 19, 2020 Author Share Posted June 19, 2020 I had very little knowledge of snow. I live in Florida. Link to comment Share on other sites More sharing options...
Sgt. C.J. Sabre, SASS #46770 Posted June 19, 2020 Share Posted June 19, 2020 14 minutes ago, Alpo said: I had very little knowledge of snow. I live in Florida. That's one of the most inspiring things you've ever said. Link to comment Share on other sites More sharing options...
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