Next consult a span table to cross reference the spacing and span to find the required fb value for that table s load limits.
Attic wieght limit.
A typical load is 5 and 10 pounds per square foot.
That means you could lay a 2 x 4 ft.
Access to attic storage.
All weight hanging from the truss has to be added to the existing dead load.
Of stuff on it.
Make sure items are spaced so that the weight is evenly distributed over the chords.
An uninhabitable attic not designed for storage can handle a 10 pounds per square foot live load.
I m guessing you don t have the plans and don t know what live load the attic was designed for.
If you want to use your attic on a regular basis or to store large items you may need to enlarge the access opening and install an access ladder or drop down stairs.
If the total weight exceeds the load limit of the truss then the truss is compromised.
An uninhabitable attic designed for limited storage can handle 20 pounds per square foot live load.
Is a safe estimate.
The joists are what support the weight.
A person might think that going by the 10 lbs psf limit that he could safely put 270 lbs on a 4x8 sheet of plywood 270 50 lb sheet of plywood 320 lbs or 10 lbs sf if you weigh 250 that means you could safely have 20 lbs up there with you on one sheet of plywood.
The dead load on the bottom chord of a truss varies with the weight of materials attached to it such as drywall on the ceiling.
The span table for a 30 psf live load 10psf dead load floor indicates a required fb value of 1 315 and a minimum e value of 1 800 000.
So if your ceiling is unfinished you have some excess carrying capacity up there.