Necessary still water airgap in order to avoid major wave – deck impacts are considered at two target annual exceedance probabilities; 10−2 and 10−4. Major purpose of study was to investigate if joint modelling of wind sea and swell was required for a reliable estimation of necessary still water airgap. The assessment shows that for the selected position in the North Sea, swell sea could be neglected. An additional investigation of severity regarding airgap between wind sea from different directions is done. The study indicates that wind sea from the southern sector seems to govern airgap requirements. The reason being that the expected number of severe storms is highest for the southern sector. Additionally, stormy seas from South are more often associated with an unfavourable spectral peak period regarding airgap than storms from North.