Hi and thanks in advance for any info. Converting a 25x13 garage into living space and when I took all the original sheetrock down I found that on the 2 exterior walls there are two 2x6's used as the bottom sill plate with 2x4 stick construction 16 on center in those walls. The 25' interior wall, on the other hand, has a single 2x4 sill plate with 2x4's 16 on center walls. I want to insulate/re-sheetrock/finish this space and the difference in 2x6 sills and 2x4 walls would cause me to have to start the sheetrock on those 2 exterior walls higher then I'd want if I use the current 2x4's due to the 2x6 sills below. Finally, baseboards and finish molding seems like it would be a nightmare given the differences in sills. What's the best way to handle this? Sister a 2x6 to each 2x4 to bring it to the edge of the bottom sill? Any other suggestions? Unfortunately, facing the current 2x4's with a 2x4 won't do it either. Thx.

House currently has a 2 car garage that has two steps up into the house. Enter directly into the kitchen so no place for wet shoes coats, etc. I was thinking of adding a small mudroom in the garage before entering the house. I would make this the same height of the house. I am guessing the best way to do this for fire purposes is framing the wall floor to ceiling with fire rated rock on the outside (as the rest of the garage is). Move the steel self closing door to the entrance of the new room. Could I then run floor joists on hangers from the new wall to the existing garage wall framing? I would insulate under the floor, walls and ceiling as well as vapor barrier for both the floor and walls. I dont think I would add any heat or ac to this room as it wouldnt be very large (dont kow how big yet, just enough for a bench seat coat hangers and shoe area to not drag in the snow/sand into the kitchen hardwood) and I figure the airflow through the current door would be sufficient. I could always enlarge the current doorway into the house so it looks better to the eye also. Thanks for the thoughts.