I am trying to air seal my attic behind the knee walls. I found a lot on this subject on the internet, but I have a problem that I can not find anything on. I put Insulation in a bag and stuck under the knee wall to stop the air there, like energy star web site stated. I have foamed all around the light fixtures and top plates. The one issue I am facing is the back 3/4 of the house the joist run side to side so I could stick the insulation under the knee walls, but the front 1/4 of the house the joist run front to back. How, if possible can I air seal these. I just rewired, to get rid of knob and tube, so I can put blown in insulation in. When I did my front room I cut a section of the ceiling out and the cold air just started pouring in the hole I cut. Please help with any info you can provide. Thanks in addvance.

Hard to give specific advice without knowing how much room you have in the "knee wall" area, but the basic solution is to find out exactly where the air is coming in. A "blower door" test is the ideal solution, but a box fan, taped into a window and blowing out might work for a room sized area. And yes, you might have to cut out the floor in that area to access the leak. The most common area for leaks in a knee wall is where the rafters meet the walls, and it might be a difficult area to seal, but it is worth it to make the effort.

I have access to most of the joist running side to side, but the front part run front to back. The back side of knee wall in the front has a joist blocking any air and I foamed top and bottom of those joists. What can I do for the ones I can not access. I can not rip up floor. Do you believe the air would becoming from where these joist meet outside wall, or the part meeting inside wall.

not knowing your house, or seeing pictures or having any knowledge of where you are working, it's pretty hard to point to the exact spot. Have you had an energy audit? have you tried using a fan to pinpoint these areas your self as I suggested?

In general, most air leaks are either to the exterior or are drawing air from anther space - attic or basement or joist bays which lead to one of these places.

this is just a rough sketch of the front half of my house. You can see the outside wall, the living space upstairs is in the green square. I have access to the crawl space behind each knee wall. When I cut out the ceiling, which is in red in drawing, I felt a huge amount of air coming in. Without tearing up floor in the upstairs, what would be another option? And where would you guess most of the air is coming from. I foamed both joist running with the knee wall toward the outside wall, top and bottom.

Air can be coming from drilled holes for wiring in the wood framing, probably something that is not accessable

I just rewired the know and tube and will be sealing with foam where I can see the holes going through the outside joist. I was thinking about drilling a series of holes on the outside wall from 1st floor and trying to foam some of the cavities touching outside wall. Do you think this would help or is it a waste?