Ooops, I misread your entry, Casciamom... I gave you the details for the 2015 BOM...
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I just went back through the instructions for the 2014 and there is no mention of backing (I even did a word-search through the documents to see if it were hidden somewhere...). I haven't finished my BOM 2014 yet so I could not tell you how much backing you'll need, perhaps someone else knows how to calculate it faster than I could...