Crown walls or superstructures on top of permeable breakwaters are often used as a measure in existing structures to counteract insufficient design protection against overtopping. These crest elements, generally located well above the design water level, have been found to effectively decrease the mean overtopping discharge over a dike or rubble mound structure. The current study focusses at investigating the reduction in overtopping which can be expected from crest elements on a permeable breakwater.