2attic loads may be included in the floor live load but a 10 psf attic load is typically used only to size ceiling joists adequately for access purposes.
Finished attic wieght limit.
In general stairs must be at least 3 feet wide and provide at least 6 feet 8 inches of headroom.
This is where dreams of adding new living space in an attic are often abandoned.
Your allowed weight and span for a 2 x8 x12 2btr hem fir based on the info you have provided is 20 psf of dead load and 30 psf of live load with minimum bearing length of 0 68.
Observing the weight rating.
Stairs can take up a lot of space in both the attic and in the floor below so they are important considerations for planning.
Modern standards call for around 12 to 16 inches of insulation in the attic and your long term utility bills would probably appreciate it.
To simplify you can place 20 pounds of dead load per square foot on your subfloor as long it s supported mid span.
However if the attic is intended for storage the attic live load or some portion should also be considered for the design of other elements in the load path.
The international residential code on which most local building codes are based requires that floors in non sleeping rooms must support a minimum live load of 40 pounds per square foot and floors in sleeping rooms must be able to handle a live load of 30 pounds per square foot.
Dead load weight of roof trusses top chord bottom chord webs weight per lineal foot plf 2x4 2x4 2x4 4 3 2x4 2x8 2x4 5 6 2x6 2x4 2x4 4 8 2x6 2x6 2x4 5 5 2x6 2x6 2x6 6 2 2x6 2x8 2x4 5 9 2x6 2x10 2x4 6 6 2x6 2x10 2x6 7 2 2x8 2x8 2x4 6 6 2x8 2x8 2x6 7 2 2x8 2x10 2x8 8 4 dead load weight of floor trusses depth in inches top chord bottom chord.
Building codes typically require that a finished space have a ceiling height of 7 feet 6 inches over at least half of the available floor space.
Finished attics need stairs that meet all of the standard staircase requirements.