Many old factory’s have these ‘wave-shaped’ roofs like [these](https://images.app.goo.gl/frvUChiF69q4fza87) . Do they have a special use to them?
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It’s for light, it’s a sawtooth roof. They came into use in the 1800’s before artificial lighting was prevalent. It is not for drainage. If anything, there are more seams/corners to waterproof than a flat roof. Imagine a northern factory with piles snow collecting and slowly melting in all of these grooves. Also, there is a lot more material involved than a flat roof, so it is more expensive to build. The benefit is with the vertical glass panels facing south, you get full daylight across the entire indoor area. More efficient work environment.
Thats just a cheap way to build a large roof that is still angled to allow rainwater to flow off easily.
Building it flat means you have to do more work with water drains.
Build it like a large triangle and it will get way too high.
Flat roofs are awkward – they tend to be heavy, inefficient of materials, and have problems with things like snow and water collecting.
So instead we use pitched roofs – these are angled so water will run off rather than pooling, and they allow us to use techniques like trussed construction to build larger spans with less material.
The sawtooth design comes from the 1800s before we had access to modern lighting, materials and air conditioning.
The shape meant we can put a normal roof finish on the pitched slope (much stronger than the glazing used at that time), and then glass on the vertical face – letting lots of natural light into the building. The sawtooth shape also means you can angle your building – by facing the glazing away from the sun (so pointing north in the northern hemisphere) you could avoid direct sun (which could get very hot) shining straight into the building.
Modern buildings don’t really use this design any more – we have better artificial lighting, and also better materials that allows us to form rooflights on a pitched face that are both strong enough to survive (unlike thin glazing), and can be frosted to allow natural light in while diffusing direct sunlight.
Modern portal frames certainly don’t look as good though…
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