Your roof replacement cost is based on many factors, including the materials you use, the pitch of your roof, any damage that might be present, and whether you choose to hire a professional roofing contractor.
Another factor that can affect your roof replacement cost is the question of the current shingles: Should you remove them, or simply place new shingles on top?
Most roofing contractors have no problem with laying new shingles over an existing roof that has only one layer of shingles, as long as they have no major damage. On the other hand, if there is significant damage or the existing shingles are in poor condition, it might be best to remove them and start from scratch with a replacement roof.
Removing the shingles can add to your roof replacement costs by requiring extra labor hours, dumpster rental, and landfill or recycling fees. But removing them is necessary if the old shingles are warped, damaged, or otherwise unsuitable for providing a smooth base layer for the new shingles.
If it looks like you can add new shingles over the existing layer, that first layer can serve as an additional moisture barrier, thus adding to the security of your roof.
A professional roofer can inspect your shingles and let you know if they can stay, or if they have to go. The ultimate goal is to provide you with a secure, sturdy roof that can last for decades. Even if you plan to tackle a roof replacement project yourself, invest in a visit from a good roofing contractor to make certain you are on the right track.