Can you install a metal roof over shingles?

Often yes. Metal is light enough that many jurisdictions allow installing it over one existing layer of asphalt shingles, usually over a slip sheet or furring strips that create a flat, ventilated surface. It saves the cost and mess of tear-off.

There are catches. Local code and the roof's condition decide it: a soft or rotted deck, two existing layers, or trapped moisture can rule it out. Going over shingles can also hide deck problems you would otherwise catch, and some manufacturers require tear-off to honor the warranty.

In Florida, re-roofing rules are strict, so confirm with your building department and installer before assuming an overlay is allowed.