Pressure-treated lumber is the popular choice, but steel framing is worth considering.
The types of available framing lumber depend on your location. In the west, treated lumber is Douglas fir that has been incised to allow the chemical preservative to penetrate the wood. In the east, unincised treated yellow pine is prevalent. The uniformity of both kinds of framing lumber can be very inconsistent and understandably so. The pressure-treating process dramatically changes the wood’s moisture percentage, which causes the boards to warp and twist. Not only will your lumber show up on the job warped, but it will also deflect once installed, as the moisture content acclimates to the environment.
To combat this continual wood movement, try to keep the lumber neatly stacked and out of the sun until it’s installed. Once installed, don’t leave the ends of posts or joists running wild for any length of time; otherwise, by the time you get around to attaching the other framing, the ends you left loose may be twisted out of alignment. Always wear gloves when handling pressure-treated lumber as the chemicals are toxic and any splinter you get will fester.
Keep pressure-treated wood stacked with bands intact to retain the shape until time of use.
Wear gloves when handling pressure-treated lumber because the chemicals are toxic. Splinters can turn nasty.
It’s recommended that you use dimensional lumber that is the full beam width rather than ganging together 2x material. Water collecting in the space between the boards could cause rot.
After you frame a deck, you might want to hide the framing. This lattice is a common item on home-store shelves and does a nice job of dressing up the deck framing on this project.
Framing with Steel
An alternative to framing lumber is to frame your deck with cold-rolled, light-gauge galvanized steel joists. There are some solid advantages to steel framing: Steel joists are lighter than wood. The span capabilities of steel are greater than wood. Steel joists are flat and will stay that way, so there is no need to crown the joist before installation. Because steel joists are manufactured they can be made to a specific length; on a simple deck you could have all the joists show up ready to install.
But steel joists are not without their disadvantages. There is a learning curve to working with steel and some specialty tools are required. Cutting steel requires extra protection like a full face mask, long sleeves, and gloves so the hot steel doesn’t burn you. You need to pay attention to where the steel bits created by the cuts are going. If left on the decking, they can cause stains; if shot into the yard, they can cut bare feet. Cut ends of steel joists need to be treated with zinc paint, very much like the cut end of a pressure-treated board needs to be treated. Most builders incorporate wood posts into the steel frame because steel posts are an odd size, making it difficult to use standard post hardware. This means you’ll have to fiddle with the post-to-steel connection.
This steel framing looks remarkably neat, because with steel there are no lumber imperfections to deal with.