Sails are not exactly designed to be installed on a pergola, but with the right measures it is possible to create a safe and resistant structure! First of all, you have to consider that sails need a generous inclination, especially when waterproof, so always plan for a 25% inclination. Then, another fundamental point is to take the measurements correctly: remember to deduct at least 35 cm at each corner to have a well-tensioned and tilted sail.