There are many different types of joists available and all of them have their pros and cons. Some factors affecting your decisions will be floor deflection, ease of installation, and workability.
Nominal lumber is a typical choice that has been used for years and years and.. you get the picture. A standard 2×12 #2 or better spaced at 24″ on center can span a distance of 15’8″ at 40 psf but only 13’11” at 60 psf. Why do you care? Let’s say you have one room with a lot of antique wood furniture where a lot of people will be admiring it. You would probably choose to only span the 13’11” at a maximum. What if we decide to use TJI’s with the same depth? We could span up to 20′, which is quite a difference.
What good does this do us? It allows us to optimize the size and number of joists, bearing points, and work that we perform. The fewer pieces we have to handle the better. What other advantages/disadvantages to using TJI’s are there? Some of the advantages are ease of installation, less work, and quality of material. The one disadvantage is that they are typically longer and can be hard to handle. A minor disadvantage in my opinion.
Whatever you choose for your joist material most lumber stores will provide engineering for your floor framing package if provided with a floor plan. You should come away with number of joists, rim joists, lengths of each joist, and a framing plan.
Now that we’ve got what we’re framing with and a plan to do so we will want to get the material delivered. One thing to remember with deliveries is put them where they are not going to be in the way of other deliveries or other work being performed.
The first step of framing, as in most home construction activities, is to lay out where everything is going to go. This should mostly be taken care of for you from the plan received with your framing package. For this article I’m going to assume you are using 1-1/2″ inch joist material and they will be placed at 24″ on center.
I like to layout the rim joists before I begin handling any joists. There are two conditions that you will encounter with rim joists – running perpendicular to the joists and running parallel to the joists. Where the rim joist is perpendicular you will have a joist every 24″ that will support the exterior wall above it. On the parallel side you will need to add a joist 5 1/2″ away from the rim joist to support the exterior wall.
To begin the layout we will make sure that the near edge of the first joist is 24″ to the center of the joist. Therefore, the first edge mark will be 23-1/4″ from the end of the rim joist – they will then run at 24″ to the edge of each joist from the first mark. This will put your 8′ piece of plywood at the center of the 4th joist.
Now you will need to continue on with the layout as dictated by your floor framing plans (hopefully your designer has included these).