Have you ever seen those bike racks which are like two sets of hooks on two linked pulleys? You screw them into the ceiling, hook on the handlebars/seat/frame/whatever and hoist the bike up to the ceiling? Well, you can use them for kayaks up to 20 kilos (that's any kayak you're gonna buy today apart from huge touring boats/sea kayaks) - I do it in my garage at home. You could even have them in your living room on the ceiling if you didn't mind the sight and had a high enough ceiling :P Or you can store them on their ends if they're small enough, which'll take up about a metre square of floorspace if you're careful! There're always ways of storing boats :P