If the trusses are truely on 24" centers, you will have to cut trusses on both sides. Simply sister them on the outsides.

Thanks for the response Handymac
You are right, I will have to basically remove a piece that is approx. 64" long, then reinforce the truss. I can easily sister the joists. Will this be enough to keep the trusses from weakening?

I have installed several of these ladders and I always completely cut out one joist/truss and then put headers across both ends using joist hangers and then frame in the rough opening to whatever the instructions call for. I would not trust sistered trusses to hold for the long term what with the weight you are going to be putting on them with the ladder and whom ever is climbing it.

That's pretty care-free advice for cutting into trusses. Joists are one thing. You might want to make a phonecall to the engineer who designed them first before you cut one (or two!), to be safe.

Headering off cuts in a truss is far more likely to cause problems than removing a section and splicing a repair piece on the outside to create a wider opening.

The bottom cord is normally a tension member, so cutting it and making a repair on the side will easily preserve the tension carrying capacity.

A headered opening that severs a cord completely will require careful design to make sure the cut bottom cord can still support a tension load.
Nails in withdrawal are not allowed for load. They are rated at zero.

Why not get a stair hat fits between the trusses?

A more important problem is that you are obviously planning to use the space above the ceiling for storage or something that would mot likely load the truss bottom chords in a manner that they were not designed to take.

Trusses save money because they are designed to have chords as small as possible and still carry the roof load. If the bottom chord is intended to carry a load the truss would be designed differently. Check with the manufacturer before cutting or adding an unanticipated load.

Thanks everyone for your responses. I am worried about cutting the trusses so I think I will take your advise and get ahold of a structual engineer. I don't need to create more problems for myself. In regards to the storage comment, I am going to store items up there but nothing overly heavy. Just some outdoor Christmas decorations such as those lighted reindeer, etc.

If this is just for storage of decorations you should get a heavy duty 22 1/2 inch wide model and leave the trusses alone.

Mightyanvil, I looked into the 22-1/2" models, but they are only good for 10' ceilings, mine is 11'3". I thought about making a box about a foot high to let the ladder legs rest on but it will take up some room on the floor, plus I would have to store it some place when not in use. I may have to resort to this box if I can't cut the truss.

Try a Rainbow Prestige attic stair. It's expensive but so are structural engineers.

Here is a link that might be useful: Rainbow stairs

If you'd like to get more selections for attic ladders.

Here is a link that might be useful: Best Attic Ladders