There are always left over materials after your new roof is installed.
After your contract is signed, the job is turned over to production to schedule, and order materials.
Production will calculate for the materials necessary to install your new roof, and a percentage is added for error.
This new total amount is ordered, knowing full well that things happen. It is a show stopper to be a bundle of shingles short. It is just an inconvenience to take back unused shingles. Having extra materials is a defense against not having enough materials.
This is the same for starter shingles, ridge cap, drip edge, Underlayment, ICE & Water, etc.
Usually left over materials will be picked up the same day the roof is completed, but it is entirely possible that it could be the following day.
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