Low profile deck using 2x4 joists by.
Making floor joist out of 2x4.
Holes anywhere in the web.
You can never ever ever notch or bore through the top or bottom flange or chord.
You can drill 1 1 2 in.
The depth or height of your floor joists depends on how far they can span without sagging.
The three main types of floor joists used in home construction are solid lumber i joists and open web floor trusses.
So one of the last things that need to be done before sheathing the deck is to fill in with blocking.
The parallel chord truss is the most common design used for floor joists.
I prefer to double the outside joists as do some deck builders which adds 2 joists for a total of 11.
Tying the joists together with blocking makes the floor even stronger and stiffer.
Editor rich bergman 2x4 joists would be sufficient depending on close they are spaced no further than 12 on center maybe even a bit closer and how long the 2x4s will span from one support beam to the next.
That means these joists can span the 12 foot depth of the deck and the beam can be located at the perimeter.
There are online span calculators available that tell you the maximum span for.
2x4s can not span a very long distance without starting to bend.
Step 1 measure the span for the trusses.
This calculator shows 2x4 s limited to 5 8 span for eastern white pine.
Nine joists will be needed for the 16 foot width.
Each type of floor joist offers its own unique benefits and drawbacks which is why those working in carpentry all tend to have their own favorite floor joist option though they are still required to be well versed in each type of floor framing.
True floor joist span calculations can only be made by a structural engineer or contractor.
Most spans are typically 10 to 12 feet so we typically use 2x8 or 2x10.
This sample table gives minimum floor joist sizes for joists spaced at 16 inches and 24 inches on center o c for 2 grade lumber with 10 pounds per square foot of dead load and 40 pounds of live load which is typical of normal residential construction.
Engineered i joists can span long distances to make a flat and solid subfloor.
In fact most have little perforated knockout holes that can be punched out with the swing of a hammer.
Notching wood and boring rules engineered i beam rules.
Making professional blocks to make the blocks i cut sections of i joist 1 inches smaller than the space between the joists.
Also the type of lumber is important.
Check out this free calculator or consult floor joist span tables for what you are doing.