bricking up a window

Hello all,
About a year ago I bought a house which is about 90 years old in western PA. One thing that has been bothering me is that the previous owner drywall/plastered over a window from the inside but they left the window on the outside. The window itself is OLD. It's single pane, the frame is cracking and broken and not very good. While I'm not exactly sure whats in there, I took a picture with my iphone from the outside HERE, and see some sort of drywall. I'm thinking about bricking it up (because it really just opens to the side of my neighbors house). I feel like bricking it up won't be too difficult.

Do I have to worry about moisture building up when bricking up the window? Do I need some sort of vapor barrier installed? Am I just being paranoid? Can I just leave an air gap? My house is old, so there is no insulation in the walls that I know of, so I'm not too worried about that. I just want to make sure I have all my bases covered before I cover up that hole.
Thanks!

 

Great picture... now if you could step back about 10 feet and give us a picture of the window that would be nice. What you're seeing looks like plywood based on the oval biscuit I see. Maybe he put in a sheet of plywood then covered it with drywall.

You should remove the sashes, remove the exterior window trim and any stops, cut off the sill nose flush with the framing, add framing around the perimeter, add a stud in the middle if needed, add insulation, then put a piece of sheathing across the exterior. Then cover that with felt paper or Tyvek. Then when you brick it up you will have to install brick ties to hold the brick to the wall in that area.

 

Sorry, I know the picture isnt great. You really cant see anything besides a normal window from 10 feet away. I brushed aside all the dirt and tried to use the flash so I could illuminate whats inside. I can post another one tomorrow.

The window isnt huge (24x48) , so could I just add felt paper to the drywall/plywood from the outside and brick it up and be done with it? Is felt paper even really necessary?

 

Moisture buildup would be a problem if the space was drafty, so if it's air sealed well and insulated that will not be a problem. Yes felt paper is necessary, I'm not in the habit of making stuff up.