I'm ordering decking for my deck and I'm wondering how much extra I should order to allow for the variation in length of the supplied decking? For example my deck is 4100 x 4500 and the decking timber is 90mm wide. So if all lengths of the decking timber were exactly 4500 I would need 207 lineal metres. Should I add 10% to this or 15%? The timber is being milled for me so it's important I order enough.
Ordinarily, I'd get 10% extra for a job like you describe. Given the custom setup, I'd seriously consider 15%, and maybe maybe if it wasn't outrageously cost-prohibitive, going for 20%. Splits, knots, and if you live in my world, mis-cuts happen. It would break my heart to have to go back for one more stick...
Plus, if you get way too much, then you'll have the fun of figuring out a project on which to use the scrap. Bench seating? Table? Quadcopter? (Okay, maybe not the last...)