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I am building a pergola (~10'x10') on my patio (and plan to build a gazebo out in the yard), but before I build it, I want to make sure I'm using the best option for lumber.
Should I use pressure-treated lumber in such an application? Or is something like cedar better? Is there another alternative I should consider?
If it's in contact with or partly buried in soil, and isn't adjacent to food plants, go with PT; it'll probaly last several times as long. If it's above grade and will dry out berween rainstorms, cedar will probably do just fine.
Note that these days there are other alternatives too -- some of the tropical hardwoods are moderately affordable and very resistant to bugs and rot. I'm seeing a fair amount of Ipe used for porch decks, partly because it's also a very hard wood -- so dense it sinks in water, which is one of the reasons it's sometimes referred to as ironwood. Warning: ipe wears out sawblades quickly (carbide recommended) and some folks develop an allergy to the sawdust. I'd be a bit more willing to have ipe near my veggies than equivalent amounts of PT, but that should still be checked on; anything bugs and fungi won't eat should be treated as potentially toxic to humans, and I've never heard how much ipe leaches into surrounding soil.
(Note: this question partly overlaps with the home improvement discussion at diy.stackexchange.com. Folks there might be able to give you numbers for how long PT fenceposts last vs. cedar.)
This is an excellent question (IMO). I've worked on a number of different projects like this. I think for things like a pergola, cedar would be a great choice. It is relatively light, is easily worked and weathers beautifully.
Pressure treated is great when it won't be visible. I find it does not stain or seal exceptionally well, however it is strong and dependable. Think stringers and joists.
If you're willing to spend a little more, one of the most weather resistant AND strong woods I've worked with is Mahogany. It is available in a number of different forms. I've even use an engineered 4x4 post that was made up of no less than 15 pieces/strips laminated together. They were pin straight, and unless viewed from a cut end, you would not know they were not solid mahogany (which would have been ridiculously expensive.
There are also a number of great systems that are effectively cases that surround another structure. Think looks of 4x4 timber, without the weight and possible bowing and twisting.
I think the answer is, "it's up to you" and "it depends". All materials will have pros and cons. PT lumber is cheaper than cedar, but cedar looks better (IMO) and smells nice. Cedar fades over time whereas composite materials might hold up better. PT lumber requires coated screws and composite materials sometimes require specialized screws. Other woods might need to be stained and sealed whereas cedar naturally resists rotting.
In a lot of scenarios, you would use multiple materials. Take a deck for example, all the supporting posts and joists will usually be PT, but the decking might be cedar or another material like a composite board.
You will need to take into account cost, lumber availability, expected longevity, and your skillset as some materials are more difficult to work with or require specialized tools.
