Just a heads up for those who do insurance work and use Xactimate. They have incorporated an autocalc function for calculating roof materials. It is used in the replace portion for RFG 220, 240 and 300 (20, 25 year composite, 30 year laminate). If you pull up that line item and look to the right of the Calc: box, you'll see a little blue cube. Click on it. You can choose the roof waste number or set it to Auto Calculate. You then set the type of valley and whether or not to include starter course in the replace calculation. This will now accurately calculate the squares of shingles required for the roof. It does not allow for cap to be bundled in which makes for a strong argument to the insurance companies for paying cap as a separate line item. We're having reasonable success with that.
I exchanged a number of emails with the Xactimate Engineer who was the supervisor of the development team for this function. He sent me the background math used for this calculation. It is very similar to what I was using in the Waste Calculation Spread Sheet i developed. That's why I switched to using the autocalc function. We have tested it quite a bit and found it to be as accurate as anything we've used. Between it and breaking out ridge cap separately, it also pays better than using the insurance companies BS bundled generic waste factors of 10% for gables and 15% for hips.
To be clear, if you aren't sketching the roof in Xactimate or importing in the roof takeoffs from an Eagle View type report, I don't think this will work. It needs all the variables such as roof area, valley, eaves, rakes, etc. in order to run the calculations.
I hope this helps some people.