When you are fitting a couch into a tight spot, there are a number of things that you should consider. Many couches are so large and bulky, they are not going to fit regardless of the ways you twist and turn them. Tight doorways are tough, but some situations are impossible if the couch is really large. TIght stairways that have multiple twists and turns are a perfect example of this. When the stairway is tight, and there are no elevators or other entryways, the options are fairly limited. If you are trying to fit a couch through a tight stairway, here are a few things you can try:
Before you try anything, check to make sure your couch will not come apart in a safe manner. Some couches, such as RTA (ready to assemble) furniture, can come apart easily and then be put back together once you get it inside. It would really stink if you went through all kinds of effort and then found out that your couch would come apart.
Many times, manpower is the issue with large couches. Try getting a few extra hands to help maneuver the couch around and twist and turn it. If you do not have the right amount of people to help move the couch around, trying to fit it through the stairway will be nearly impossible. Get all the help you can get so that you can try every combination.
Once you have the proper manpower, then you can look at turning the couch vertical. Often in stairwells, you have plenty of vertical space. The couch is long and narrow, so the best way to make it small is to turn it up on its end. This is a great way to try to fit the couch through a stairwell, and can often solve your problem.
Another option you can consider with a large couch and a tight stairway is utilizing a large window. Windows are usually not a good choice when you have to go high off the ground, but if you have a big enough window you can hire a pro to lift it with a pulley. This is not an option that you should try unless you have the expertise, but it is an option you can consider. Many apartment buildings in New York offer large windows for just such a purpose, for example. If this is possible, it could save you a ton of money.
Ready to assemble furniture is really the best answer if you find that you can not fit your existing couch through the stairway. While ready to assemble couches used to be completely cheap and ugly, they are no longer all created equally. There are custom made ready to assemble options that would blow you away, and that are made as well as any type of furniture out there. They are no longer all cheap particle board nightmares. The custom made options are made with solid wood like oak and ash, and are often guaranteed for life. Check these out if you are unable to solve your stairway problem.