I am going to install 30X54 attic stairs.Will have to cut a few joist in ceiling.Only place to put stairs.What is the best way to support the joist after I cut a few of them.Would rather the house does not cave in. At least when I'm in it.

 

Locate the ideal location. Your instructions will give you the optimum opening size, which should include joist bridges. You will need to cap each joist end with 2x lumber to the adjacent full length joists. This measurement will be about 3 1/2" longer than your staircase actual measurement. Once this is done, you can run a 2x the long direction to define the width of the staircase plus 1/2". If the location is in the middle of a super long unsupported run of joist, you may want to build a jack tee to hold things up until you get it all tied together.

If you have trusses, you should try and use stairs the width of the trusses. The manufacturer of trusses frowns on cutting their product.

 

Easier and faster to just lay a 2 X 4 laying flat across the joist in the attic and screw it into the joist for easy removal when done.

 

That is what I have done in the pass when I put in a whole house fan.I am just wondering if I'm cutting to many of the joist.In the hallway (14 feet long,second floor) the builder put an attic opening off about 3 joist wide (cut one joist-to make about 26 wide opening). Then in the ceiling I have another part of the ceiling that is not cut (about 39 in long). Above that (39 in)is a support for the peak on this section of the roof. The roof is in two sections,with a little opening from this higher section to the lower section. After the 39 in part of the ceiling I have a whole house fan about 36 in long in the ceiling. I believe I had cut two joist back then (about 20 years ago). To install the new attic stairs I need an opening about 54 in long.So I will have to cut another joist.I will be taking out the whole house fan and installing the attic stairs in place of the fan.I will be closing up the old opening to attic after the new stairs are done.
If I cut another joist and block it would it be OK. From what I can see I have 3 joist cut already and want to cut one more.From what I have read I do think it would be OK.Just wondering from some one with a little more experience.

 

It's really impossible for us to give a good answer without some measurements, a diagram of exactly what the framing looks like along with where the load bearing walls are in relation to these openings/cut joists.

Generally one joist can be cut and it can be safely headed off to the adjacent uncut joists on either side. But you can't do that on both sides of that same joist (putting twice the load on that one joist) and you can't do that when you cut 2 joists in a row... you have to take extra framing measures to distribute the load.

Depending on which way the attic ladder runs, it might be wise to double the joists on either side of the new ladder seeing as how they will also have to carry the weight of the person on the ladder as well as whatever he is carrying up/down.