Garage loft stairs

[Brno8x57]

I have a 20x25 detached garage with a loft. Loft floor joists are 2x12 OC 16 inches and span the 20 foot width.
Previous owner installed a 24x48 cutout for pull down stairs, installed perpendicular to the joists so three joists were cut. Double Stringers and headers were used.
I would like real stairs and want to install steps running them parallel to the joists.
I will remove the current stairs and replace the cut joists. Can I double up on two of of the joists and space them 24 or 32 Inches apart so I can install a pull-down stair case in them? Basically I need a 2x12 foot hole for the stair case.
Loft is used for storage. My loft joists are not needed for integrity of the garage, they were added to create storage.

 

[slackdaddy1]

you can a pproach it 2 ways, the technical, by the book way. Or the "wing it"

The Technical way: 1st question is what type of storage? you would need to know the PSF dead load it would see, then do load span calculations to see if doubled up joist on each side of the opening will handle the load.

The wing it way:
Move the joist to create your opening width, doubling them on each side of the opening, add double headers at each end of the opening to carry the "short" joist.
If worried, double the joist with a micro lam instead of a 2nd 2x12.

If you ae going through the trouble, go with a high quality 32" wide pull down,, you wont regret it.

 

[Brno8x57]

I used 30pound live load for my back of the envelop calculations, Storage will be typical garage stuff, hand tools and extra junk. mostly spread around the perimeter. The area around this opening will be empty.

 

[rlitman]

I put a roughly 8' deep loft in my 20x20 garage using 2x10 joists spaced around 12" OC (16" spacing would have been fine, but closer spacing worked out easier to do). But here, I'll point out that my joist clear span is barely over 19' (20' is the garage's exterior dimension), and those few inches can make a big difference at this area in the span tables.

What I did was double up on the last two joists, spacing the doubled joists 22.5" away from each other inside. That's the same spacing as you'd have for 24" OC attic joists, so it fit a folding attic ladder perfectly. I also made the outermost joist a 2x12, so the 3/4" plywood floor rests on the inner one, leaving a lip (above the adjacent 2x10) at the edge to keep things from rolling off.

 

[QwikKotaTx]

I just installed a 22" wide set of pull down stairs in my garage and I am surprised how narrow they are compared to the 30" wide version in the house. Feels cramped to my feet.

 

[Brno8x57]

I would love to go with 40 inches and use pre-made stairs that I have but that is a lot of open space. It would need 2 joists removed
From half the width of the garage vs 1 for the 24 inch model.

 

[Brno8x57]

According to woodbeamcalculator.com with 30 live load, 20 feet span, double 2x12 allows for 28 inch spacing for joists. I’m assuming that if all joists in a floor can be treated like this (28 oc doubles up) then it’s okay to do it for just two and go to 16 oc for the rest? That gives about 25 inch opening for the whole span, I’ll add headers at 12 feet.
Any error in my thinking?