Framing Roof Joists for Addition when top Plate is not Level

I am involved in a project where I am adding an additon to a ranch house. House is about 25 feet wide about about 40 deep. Most of the projects I work on are total gut jobs so I dont worry about saving existing structure. However this house has a really good first with new kitchens and baths so I want to keep from demoing the ceiling and ceiling joists.
Joists go across house as expected. The top plate on the rght side of house is about 1 inch lower then the left with a slight(1/2") pitch toward the back.
I was wondering what methods others use to level the top plate before adding a new floor in cases where the existing ceiling and ceiling joists are to remain. In cases where I am am demoing the existing celing joists and the slope isnt bad I sometimes shim under each joist.
However for cases where I am leaving the existing ceiling joists (to support exisiting drywall ceiling) and installing new joists I have been doing is scribing and cutting the rim joist to follow the contor. I like to install a rim joist because otherwise otherwise I end up with a bunch of point loads which dont line up with the stud wall(since the existing joists line up with the stud wall).
What I did in the past was a buy a engineered wood rim joist one size over(assuming slope is less then 2 inches). I placed the enginnered joist on the top plate temporally, shiming the low side until level. I then ran a scribe down the outside of the building along the top plate. This left me a line on the rim joist that followed the slope of the top plate. I then trimmed it down with a circular saw so now the contour of the rim joists makes the contor of the top plate.
This was time consuming but seems to work well. One thing that makes it even mroe time consuming is the fact that the existing ceiling joists in most cases extend flush to the edge of the top plate. This causes me to have to cut these back 1 1/2 ". I then connect them to the new rim joist with simpson angle brackets.
I was wondering how others do it when framing new floor joists in parallel to existing when top plate isnt level.
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snipped-for-privacy@yahoo.com wrote:

What first comes to mind is, provided the structure below is sound (not sinking/settling/rot/decay i.e. why is it out 1"?), why would you be worrying about 1" in a remodel of a house where the structure below is likely also out that same 1"?
An inch out of whack isnt much to deal with in construction but it also isnt much for the homeowner to live with given the first floor is likely the same. How do you deal with exterior details that will all now have to be tapered or cheated to accommodate the leveling of the new construction? The outside walls will be taller on one end than the other and so on. Do you cheat the inch out in the siding? Taper your last course? Will the correction show in the outside corners? Are the first floor walls plumb? Leaning? As I said, an inch aint a biggie, but the point is still the same. Its not to say it cant, or shouldnt, be done just why and what are the repercussions of it.
Your first concern should be where did the inch come from? After that would be why the need to level the second story in the first place given the rest of the house is out an inch and seems to be acceptable enough to the occupants that they want to save it. After that would be how will you deal with the everything else affected should it be taken out.
I cant say we have ever done a second story addition over a first floor which was out of level enough to be concerned with so I can only speculate that in this case I would likely let the second floor mirror the first. If it were out enough that the we, and the homeowner, were concerned with it we would likely sister new joists/sleepers inbound of the walls leveling the interior floor a bit but leaving the new second floor exterior details parallel/in-line with the first. This would result in a more level floor in the second story addition though it would have to be taken out in the interior finish.
The way I look at it is, imagine you had a structurally sound home that was leaning 6" out of plumb in 8'. When you add the second story do you build it plumb in effect putting a "kink" in the house or do you carry the second floor up matching the first so from the exterior it looks good? This is only an inch but the principal is the same.
As for cutting back existing joists we find it is fastest with a chainsaw. Snap a line, square down from that line, and do a nice job cutting them back. If your no good with a chiansaw a sawzall is second best but 1/10th as fast. I dont consider a chainsaw a great carpenters tool but in some cases its handy and a real time saver as long as you can cut a clean, straight line.
Mark
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I'm with mark on this one. I've always believed that once you have a foundation, it is what it is after that. 1" out of level in 30 feet is annoying, but it is within tolerance. I once framed shed roof where the upper bearing point was level but the lower bearing was 1" out of whack in 32 feet. I gnashed my teeth for quite a while before we just framed it and it would take an experienced carpenter to notice it when we were done. I would be more concerned that it be flat so you don't get any whoop-de-doos in your eve or ridge.
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Very good points all around. The 1" isnt noticeable inside. You are right, any changes I make to correct this issue will cause my side wall/facade to need corrections to discount this inch. We are adding a mansard roof on top of the existing structure so it could be really tough to hide that inch.
On the lower floor there is a room that spans the 30 feet and it isnt noticable there. On the addition floor there is a center hall and rooms on each side that are around 13 feet wide. If I didnt notice it in the large room breeak the 1" up into 2 rooms and a hall should certainly hide it further.

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