Eli5: Why do houses have a triangle shaped roof? Why not flat?
In: Engineering
Almost every single residential building in major east coast cities have flat roofs. They are usually pitched in one direction or have roof drains to collect rain and melting snow. You are not as likely to see this in the suburbs because it’s a more expensive construction technique.
It’s easier to make a waterproof roof if you can overlap shingles and have water only running from the top one to the bottom one. If you have a flat roof, you have to perfectly seal the whole thing, often with hot tar, and it doesn’t look as good. You’d usually only build it flat if you want to use the roof as a floor for living area. In colder climates it’s also harder to get snow off a flat roof.
Some houses do – but many would be found in drier parts of the world. In more temperate and cooler parts, you would need to be able to have snow/rain easily disperse from the roof instead of it pooling. If this happens, especially with snow, the weight of it might be structurally damaging. With rain, this would cause puddles to form which could leak into the house.
As someone with a flat roof I will tell you that it is very difficult to maintain. Because water does not so simply roll off the sides it will collect on the top and can seep into your ceiling. We have had to do repairs because of it
Also animals like raccoons and squirrels can get on top easier and do damage to the roof.
Houses have triangle roof so that rain and snow can fall down the sides and not create a big puddle on top
Houses in the middle-east tend to be byzantine influenced and are flat roofed, and square in shape. They hardly ever have triangle shaped roof’s due to the rarity of rain, thus if it were to rain it would evaporate quickly in a few days and of course it never snows in the middle-east at leadt not in the gulf council countries.
Snow, particularly getting rid of snow
If you live somewhere that rarely gets snow then flat roofs are common, you’ll see them all around the equatorial region from the Caribbean to the middle east
If you live somewhere that gets a sizable amount of snow then a flat roof is just asking for disaster.
Snow weighs 21 pounds per cubic foot, if you’ve got a 20’x20′ roof that’s got a 12:12 pitch(sharp 45 degree roof) then it may only hold 6 inches of snow on it or 4,200 pounds. If you’ve got a flat roof and you get a blizzard that drops 3 feet of snow then you have 25,000 pounds of snow on your roof and you run the risk of your roof collapsing.
Flat roofs are common in places that have less precipitation. The slant helps in precipitation to slide down instead of getting accumulated at the top which can cause an issue to the structure
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