A. Actually, with snow, you don’t get more load along the slope of the rafter; you get the same load as a flat roof with the same run would get. This is because as snow falls vertically it spreads itself further along a sloping rafter and so accumulates less depth. The BOCA code recognizes this and allows you to use the horizontal projection of the roof when calculating snow loads. BOCA also allows you to reduce the snow load for roofs with slopes greater than 30 degrees, presumably because snow will slide or blow off steeply pitched roofs.
For dead loads, you are correct. Technically you should use the actual rafter length when adding up the weight of roofing materials. However, in my practice, I typically use the horizontal run of the roof for both types of load. To do this, I use conservative (too heavy) dead loads and full snow loads regardless of pitch. I ignore the slope...
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