i have been a builder close on 50 years ...half the span +1 is the norm ..not 2 as john says ...uk building inspectors are the best in the world ..they accept half plus1 ..so on a 6ft span @ 16"centres your fine
A 'rule of thumb' for sizing timber joists in imperial units is to divide the span (in feet) by two then add two to the answer. This will give the joist depth in inches. It is the depth which is the critical dimension. Joists are usually 2 inches wide.
So 6 divide by 2 = 3 +2 = 5 inches deep x 2 inches wide.
The answer is NO. 4 x 2 is too small to take the normal loading.
You can use them if you halve the span by building a small "sleeper wall" halfway across. The sleeper wall should be built with voids to allow for air circulation.
You could,if there's no code inspection to pass. As long as you would only have very light loads it would work.
If spanning 6' and 16" o.c., could I use 2x4 floor joists for a shed?
