problem with wall near chimney

[Barry J]

My chimney goes up thru the middle of my ranch house. I have been having flaking and a yellow stain on the ceiling, right where it joins the chimney. I thought it was the warm air going thru a air leak and causing condensation with the cold air of the chimney. It was better in the summer, but it is starting to get cold again, and is starting to flake again. Last spring I went up in the attic and sealed the metal flashing against the chimney, but the problem comes back.
Now up in the chimney, The rafters go around the chimney, but has a 1-11/2 inch space around the chimney, ..some (half around) has the metal flashing against the chimney, that I sealed. But, the other section, just goes all the way to the cellar.
Since the rafters (wood) does not go all the way around, I think the air is still mixing and causing condensation.
Can I box in the chimney with 2x4s or 2x6s and throw insulation inside, and then seal that up?? Or will that cause more problems.
I am getting frustrated.
I will try to post pics.
Thanks, Barry

[pushkins]

The side that the stain is reoccurring.....is that the side that has no chimney flashing in the attic area ?
Yes, you could add the extra 2x4's on the side that has the gap all the way down to the cellar, add some metal flashing and caulk in place, this would stop the draft.
It's not the cold air of the chimney it's the attic space cold air mixing with warm air. Make sure that the chimney is in fact flashed correctly on the roof side, often a small crack in flashing caulk lets in small amounts of moisture from rain etc.
The chimney itself should never have insulation or any flammable product installed against it. Some would argue that "Rockwool" insulation can be used as it is non flammable DO NOT use spray foam or any solid foam material.

[Barry J]

I figured that my first step would be to have my chimney re-lined with 4" stainless steel tubing, then re-cap the chimney, to solve my "rain water" leaking out my brick in the house that seems to be happening. Then put rockwool into the space around the chimney and then seal it with metal flashing or rock board on top of that to solve my condensation problems