To assess achievements in any job, it is helpful to note starting conditions that had been coped-with for many years,
A 3/8" plywood flimsy skirt about the "hole" was 16" high, far taller than surrounding R19 loose-fill insulation. Somehow from the top step of a step ladder, one had to place weight upon the wobbly skirt, to hurdle over tripping electric power cables and to land on a single 24" path to the furnace platform. Furnace filter changes and more demanded safe access.
All of the landing area is over house heated space and should have remained R38, undisturbed. R38, at R2.2 per inch, demands 18" insulation depth, not achieved anywhere. If insulation over 10% of heated space is only R8 and the remainder were actually R38, the effective R-value is as 1/(Reff + 3) = .1/11 + .9/41. Reff = 29. If the remainder is only R25, Reff is 21. In Metro Portland Oregon at Fall 2023, there is a $1.25 per sq ft rebate of cost paid for added attic floor insulation. Installation specifications: Existing insulation must be R-18 or less. Must insulate to R-38 or greater or the fill accessible cavity.
I would do further math to prove qualification at <R18, where space with no insulation, under the furnace and in general near roof eaves amply brings down the average.
The insulation space under the furnace platform is 10 1/4". I will build framing in new safe passage to the furnace that again is 10 1/4" tall. I want no trip-edges. Where the found loose-fill so-readily collapses to 3 1/2" depth, new insulation should be in the form of tough and resilient R25 fiberglass batts 24" x 48" parallel to the trusses, for total then of almost R38. Very importantly in this, all space with no insulation, must be filled. This might demand temporary jacking of the furnace off of the messy flooring, two heavily-nailed layers of 7/16" OSB.
Get on now to the core purpose of this post, considering lessons learned with a unique attic ladder.
A fire-rated ladder must not be compromised by a gap about the ladder frame, only concealed by wood trim. This framing is trimless as seen in the full-scale drawing that follows.
Limit arm upper pivots are 5/16" x 2 1/2" lag screws embedded strongly in the ladder rough frame (well-strengthened truss bottom elements).