It says max load is 100 lbs/SF. What happens if a 200 lb person carrying something heavy walks/jumps down them? This could easily be 300 lbs of pressure on just one spot? (Ie big teen with school backpack).

Hello, for a staircase with 42'' treads (2 stair stringers of 18 treads), the staircase can support 3-1/2 SF x 100 lbs/SF = 350 lbs per tread x 18 treads for the staircase = 6300 lbs. The load is distributed over the entire staircase. You must use 3 stringers for a staircase over 42'' wide. Thanks