Observing the weight rating.
Finished attic wieght limit.
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.
This is where dreams of adding new living space in an attic are often abandoned.
Stairs can take up a lot of space in both the attic and in the floor below so they are important considerations for planning.
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.
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.
This is because the ladder is simply not strong enough to support any more weight and you are putting unreasonable pressure on the attic access ladders every time you break the weight limit.
Modern standards call for around 12 to 16 inches of insulation in the attic and your long term utility bills would probably appreciate it.
In general stairs must be at least 3 feet wide and provide at least 6 feet 8 inches of headroom.
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.
It is vital to observe the weight rating and make sure that you comply with it at all times.
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.