Same applies for snow load. The main chunk of the code will let you calculate snow load for a standalone flat roof, you need the commentaries to determine build-up, sliding and valley loading.
It is rather dumb in one way. But in an entirely other way it's much nicer. I've memorized the values from the main chunk of the code that are generally applicable to my work. So I really only need the smaller commentaries during the work day. It's a significantly smaller book.
