What can you do with a triangle? A Roof!

First thing first: a roof! How do you draw a house? A square + a triangle on top of it.

Look around — on the street, in a movie, in your photo album – to spot roof shapes. Sketch them. Notice that some roofs are steeper than others. Why?

In mountainous regions, where snow falls heavily, roofs’ slopes work like slides for snow and rain. The steeper the roof, the quicker the water falls on the earth, so that the roof doesn’t leak.

This steepness is called in architecture roof pitch. Let’s measure it out! Take the vertical rise of the roof and divide it by the horizontal span. You end up with the slope, that is the pitch. The resulting number is a fraction: the higher the fraction, the steeper the roof. The pitches range from nearly flat (minimum vertical rise) through low pitch to steep pitch (see the Gothic churches’ endless roofs, such as St Stephen Cathedral in Vienna).

Pitch matters! Not only for water leaks, but also for building materials and even building appearance. Some materials don’t fit a steep pitch because they may glide. Stone roofs (yeah, traditional building has interesting techniques, such as thin stones for roofing material) need a peculiar pitch: not too low to allow water leaking, but not too steep to allow stones’ sliding.

Can you spot other roofing materials around you? Recall your travels, the movies you’ve seen (many display intriguing landscapes, maybe you pay now attention not only to the plot, but also to the setting).

Next time you walk downtown with a classmate you want to impress, talk like a pro: “That’s a gambrel roof!” “Whaaat?”, the other would gasp. “A Dutch roof!”, reply confidently. A gambrel roof is made of a trapezoid + a triangle on top of it. Why? To gain more living space while not wasting building materials for high roofs. The attic is a useful space, not worth wasting it, above all in downtowns, where land is so expensive. The gambrel roof furnishes a comfortable solution, because it hides one more floor into the attic (in the trapezoidal part) and cuts the amount of building materials used to cover the building (by changing the slope of triangular roof on the top).

Gambrel is a word mostly used in the US and UK. In other places you may hear curb roof instead. Mansard roof (or French roof) looks similar, although it has a different story (see François Mansart). One of the most visited streets in the world is the Haussmann Boulevard in Paris. Find a picture to look at the buildings lining it: apartment blocks whose last floors are within mansard roofs.

Nowadays the connection between pitch, climate and roofing materials is loose. You can build a flat roof in a rainy place: no worry about seepage and dampness. (Fit the building to its neighbors!) Yet, the beauty of architecture comes partially out of the building surroundings: the landscape, the climate, the materials at hand. There’s one type of roof that will make you dream. Frank Lloyd Wright’s prairie houses seem to melt within the land (Frank Lloyd Wright: The Eaves Master). The low-pitched roofs stretch out enormous eaves as if gently shadowing the horizon. See how many things may spring out of a simple roof shape? Just use it wisely!


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