Building a pergola over an existing deck (going on five years old but still in excellent shape) that’s also made of treated lumber. Also in a neighborhood that’s not super high dollar - fences and decks are generally pine, not cedar, redwood, or tropical hardwoods.

In my case, is there a major drawback to using treated lumber for my pergola build? I understand it’s not as long-lasting generally as cedar. But if it’s stained regularly, installed in a shady area to begin with, and sized to help prevent warping (using 6X6 posts, 2x12 beams, and 2x10 rafters), is this going to be a problem?

Getting a number of comments online against use of treated pine, so just curious what the posters here think.

 

A big thing affecting how long treated lumber lasts is what you buy. There is lumber treated for ground or in water use that will last a very long time. Much of what is sold in big box home centers is very minimally treated and 2"x lumber is only rated for above ground use while 4", 6"x lumber is treated to the lowest level for ground contact. If you want your pergola to last using lumber that is treated to a higher standard is probably the easiest way to go though you may have to special order the wood, and when you get it read the tag on the end of each piece to make sure you are getting what you ordered.

Cedar and redwood are great woods but are no longer the great stuff they used to be, especially redwood. Old growth redwood was incredible but is almost impossible to buy anymore. That leaves farm raised fast growth redwood which is totally different in terms of hardness and rot resistance. It's still good but I wouldn't regret not using it.

 

Around here, decks are usually cedar but the structure underneath is PT because it's not worth the extra cost - a lot of the price difference is just that cedar is prettier than PT.