Hi folks, this is my first post here, although I've been reading for months, and researching for my own project.  There is some overlap between my issues and those posted by nikkihorz, but I decided to start a new thread instead of jumping in on the other one, since there are a few important differences.

I live in Toronto ON, and am renovating a 2.5 story brick house. It's gutted, completely accessible throughout the inside.  The brick walls are load bearing (ie: joists penetrate the brick by about 4") since the house previously had no interior stud walls, only lathe strips tacked directly to wood spacers built into the brick wall about every 12 courses.  I have gutted all the lathe and plaster and framed 2x4 walls with about 1.5" space behind the studs to allow for shoving insulation behind the studs.  To create an exterior air barrier I am putting Typar behind the stud walls directly against the brick and taping the seams / tacking the top edge between two top plates.  I will be spray foaming the header spaces and cutting a narrow 1" piece of subfloor (also next to the brick, behind the stud wall) so that the foam makes a continuous seal from the Typar on one floor up to where it starts again on the next. The purpose of the Typar is to prevent exterior air that works its way through the cracks in mortar joints from moving into the wall cavities.  I am in zone 6 so I will need a continuous 6 MIL V.B. on the warm side of my insulation.  I'm trying to prevent condensation from occurring on the insulation side of the VB in the summer (cooling season).  I'm counting on the vapour permeability of the Typar to allow any escaping air from the interior to still dry to the outside, although I'm not as worried about escaping air in the winter since I believe that the stack effect will be pulling most air out from nearer the top of the building.

 --- SO, Dana1 wrote in the last post by nikkihorz about the importance of the air barrier, and talked about putting cardboard between the joist cavities under the knee wall.  That is assuming that the insulated wall IS the knee wall, right?  ie: insulation travels up the wall for the floor underneath (the 1st floor, in nikkihorz's case, the 2nd floor in my case) then travels horizontally in the ceiling joists over to where the knee wall starts, then up the knee wall to connect with the attic rafters.  From what I've been reading, and I'm NOT an expert, just so you know, Dana1's sealing of the joist cavities is indeed a smart idea for that configuration.  I wanted to share with you guys what I've been thinking about doing as an alternative, in the hope that I can iron out any kinks in the plan:

I'm planning to put blocking between the joists holding up the top 1/2 story floor.  There's an important detail here, which is that the blocking will be a part of the air barrier, ie: on the cold side of the assembly.  The Typar from the floor below will be taped directly to that blocking and foamed at the seams.  In order to get maximum R-value of insulation at this vulnerable connection I've actually removed the bricks between the joists (since they were embedded, but it is the top of the brick wall before the roof starts) and I'll be moving the blocking back closer to the outside of the brick wall.  The base plate of the roof runs across the ends of those embedded joists, so the block will serve to reinforce the structure as a replacement for the bricks that were removed. It also allows for Roxul to be put between the joists in that 9" cavity instead of the bricks.  For ventilation air from the soffits I will give a 2" gap between the blocking and the base plate, then use cut pieces of XPS to continue the line vertically into the attic rafters, where it will terminate in ventilation panels that run up to the peak.  All the seams will be can-foam sealed.  Air will be able to come in through the soffits and be directed behind the blocking and the foam and into the ventilation channels.  That should take care of having an uninterrupted air barrier up to the top of the roof ( I have collar ties down about 2 feet from the peak to allow for air to circulate and escape through roof vents.  

The benefit (I think...) of this assembly is that the line of the air barrier is simplified, and therefore hopefully less vulnerable to leakage.  The insulation and 6 mil VB will be installed in a straight line right through the joists of the 2nd floor and up to the attic rafters, then up the rafters *** through the juncture of the knee wall*** up to the collar ties where it meets the line from the opposite wall.  The significant difference is that I won't have to twist and turn the air barrier or the vapor barrier around the knee walls, although I'll have to cut slits in the VB to go through the knee walls (and use acoustical sealant sealant to keep it tight).  

I'm wondering if any of this will help nikkihorz, and if anyone reading this can find a problem with this plan?

Also, If Dana1 can suggest at what point in the process the blower door test is advisable - after the air barrier is installed but before insulation, or after the whole assembly of air barrier, insulation and VB?

Thanks!