Most coastal environments also have high wind velocity issues, as there is a lack of protection from nearby buildings often on more than just one side of the property.
Rain driven by the wind can cause issues of wood rot to windows, balustrade hand rails, timber decking and even the houses timber window frames. The external features of the house are damaged the most, especially the outdoor entertaining area. Pergolas are often an add on to a house, to provide an outside entertaining area and can be free standing or attached.
Attached pergolas can however increase your risk of the house roof gutters over flowing if the storm water is directed back towards your roof gutters which is quite common.
The most common damage to pergolas in a coastal environment, is due to wood rot. Unprotected beams, purlins and posts, near the top and at the base or just rusted post shoes.
The timber used in pergolas was primarily Oregon timber in the pre 1980's, this is the most susceptible timber to wood rot. More modern timbers used are CCA, these were used from the early 1980's and still used today. Newer timber treatments such as LOSP have become very popular as the timber used is often laminated from short offcuts. This gives a very strong timber, without wood knots, however any ends cut by the user must be re treated to prevent future wood rot. Wood rot in houses only a 10 years old can be seen if you look at the corners of the house fascia, this is unfortunately very common as the LOSP treatment is solvent based and needs to be painted over or it turns back to untreated pine over time.
The connection point to the house is critical to stop dynamic movement of the structure, that can cause weakening to the whole pergola. Uplift from strong wind can easily remove roof sheeting, especially polycarbonate sheeting that relies on a small dome head Neoprene washer as a connection point, to clamp the sheeting to the timber purlins. These dome head washers perish over time and can crumble away, resulting in sheet lift during high wind.
Free standing pergolas, rely on the roofing as the main diagonal brace, to stop flexing and require knee bracing to the posts or double Tornado type post shoes on each post.
The other alternative is cross bracing or slat walling to reduce movement and brace the structure.
So if your at your next open inspection, give that pergola post a shake, look at the post and beams for signs of wood rot or rusted post shoes. Then think of the expense of removing or replacing the structure.