Most homes in the United States feature roofs that are pitched (i.e.,angled) and covered with asphalt shingles. Roofers lay down these shingles in overlapping courses, or rows, that allow water to shed from them, waterproofing your roof. For asphalt shingle roofs, the most common racking arrangement will include flashings and rails. A flashing is a sheet of aluminum that slides up under several courses of shingles and attaches to the rafters of your roof. Aluminum rails are then connected to a standoff (small metal pole) that attaches to the flashing. Solar panels will be laid on top of these rails, securely connected with clamps.