Yes, roof shingles can be pressure washed. However, it's important to use the right type of pressure washer and the correct settings, or you could damage your roof or void your warranty. Always start with the lowest pressure setting and work up from there. You should also hold the pressure washer nozzle about a foot away from the roof shingles to avoid damaging them. When in doubt, it's always best to consult a professional roofing contractor.