Walls and Ceilings - Moisture issue

We recently added a second level to our home, which resulted in our brick-faced chimney extending through this space and out the roof. The chimney encloses two flue pipes for our furnace and fireplace, and runs up, along an exterior wall, but in the interior space. The brick work is not decorative in the least, and therefore will be hidden with a stud wall and drywall.

My issue is that I've got the framing for this wall up and insulated using unfaced fiberglass batting along with a plastic vapor barrier. Now however, I'm noticing moisture collecting on the vapor barrier in this area, as I've determined the bricks give off just a little bit of heat, which is enough to cause condensation to collect. The second level is currently unheated, and in Northern MN, it's not terribly warm this time of year, which likely isn't helping matters any.

Any ideas on how I can properly correct this so I don't end up with moisture/mold growing behind the drywall once it's up? Would using rigid foam insulation make any difference, or will the same issues crop up? Thanks for any insight you may be able to offer!

About a year ago, I saw a second floor added to a house, enclosing the chimney the way you described. It looked like a big mistake, to say the least. I can't believe it complies with code.

The brick has to breathe, so don't put anything directly against it. I wonder if you can create an air shaft along side the chimney with an exhaust fan to extract the moisture. It's just a thought but something has to remove the moisture.

Hi H8, to add to Pulpo's comments, is the moisture you are seeing on the inside or brick side of that plastic. Adding heat doesn't cause condensation. It is when that warm moist air cools that the moisture condenses out.

I agree with Pulpo that chimneys and wood framing are reason for concern, even though they are built that way. My personal approach would be to install some sheetrock between the wood and brick, but still maintain the required air gap.

Bud

Chimneys have gone up through second stories of homes on the inside for years. I'd imagine it is condensing on the chimney side of the plastic where it is warmest.

Your mistake is the vapor barrier is on the wrong side. You have it likely on the cold attic side. You need to have it on the warm chimney side of the framing, in your unheated attic space. Then the open insulation would be in the stud cavities, without being plasticed on the attic side.

Thanks for the replies all - I certainly do appreciate all your thoughts.

As was guessed, the moisture is indeed collecting on the brick side of the moisture barrier, as opposed to the room side. I can certainly give the idea of moving the moisture barrier to the backside of the wood studs (nearest the brick) and see if that solves things. I'll also reduce the amount of insulation so that there is a larger air gap as was also mentioned.

Thanks again for the ideas!

Then what you can do before you button everything up is take a sneak peek and remove a batt of insulation and see if you see any more moisture on the vapor barrier. But make sure you do a nice tight fit with the insulation job.

I have a question. If you move the vapor barrier to the brick side of the insulation, will you move it back when that space if finished and heated?

The problem is, the VB is where it belongs, you are just not heating that space at present, so the VB gets cold and warm moist air from the other side is reaching that cool surface. Here is a thought. Is the moisture from the bricks still drying? If so, remove the VB and insulation and let it dry. If the chimney has been up long enough to essentially dry, then where is the moisture coming from. Chances are it is coming from the basement or floors below, leaking air into the space around the chimney. In that case, install air barriers where necessary to block the leaks. A typical energy auditor suggestion is sheet metal and fire rated caulking or foam to seal around the chimney in the basement. Otherwise, rising warm air continually flows up through that space.

So regardless of what you do with the insulation and VB, you need to block all air flow from inside the home into the space around the chimney. With that done, there may be no moisture to condense to start with. If the space up there is going to remain unheated, then you may not need the insulation and VB at this time.

HOWEVER, not being sarcastic it's just that this is important, leaving the second level unheated you face the same dilemma throughout that second floor. An attic is vented and air sealed from the heated space for this reason. I don't know at what point you have stopped, but there can be issues. Example, when people try to shut down areas of large older homes to reduce the heating costs in the winter they often find mold growing on walls where there was never a problem.

Take a look at your overall picture and follow the basic rules of blocking moisture and warm moist air from entering a cool/colder area/surface.

I hope this helps.

Bud

Thanks Bud - you are correct that the area will eventually be heated. The second level will ultimately house bedrooms and a family room once completed. At this stage of construction however, I simply don't have the heat installed yet.

The bricks for the chimney I would think have had a chance to dry, as they were put up in August. I too originally thought the problem might be from the lower level leaking heat, but around the base of this chimney on the second floor, I have spray foamed the area to seal it up good. Therefore, my best analysis is that the heat from the furnace flue radiates just enough through the surrounding bricks, as I can feel a slight temperature difference when I put my hand on them. And due to the upstairs not currently being heated, those bricks are warmer than the room itself at this point.

Thanks again to all!

The question still stands, where is the moistute coming from. Heat from the brick chimney would only carry moisture if the bricks were still wet. Your home is filled with moisture from showers, cooking, perspiration, plants, and other activities related to water.

Where are your dryer, bath, and kitchen, exhaust ducts vented too?

Heat only increases the capacity of air to hold water, thus when it cools the water condenses out. But the H2O has to be coming from somewhere.

Bud

The moisture can be entering from the top of the stack itself, that is the portion of it that extends above the roof. The stack was once all external & now a section of it is internal. As I said before, the brick breathes, releasing & absorbing moisture, all the time.

As for where the moisture is coming from, I suppose it could be the bricks themselves. How long do bricks remain wet?

When it was originally a single-level house, we still had the chimney running inside, as it was also used for our fireplace. On the first level, the brick isn't too bad, so it's exposed. When it was extended up through the second level, they didn't use anything decorative, and it would kind of be an eyesore to keep it exposed. That's why I planned to frame around it.

All of the appliances (kitchen items, laundry, bathrooms, etc.) have proper vents extending from their location on the main floor up through the roof, so nothing ending up in the attic or anything that should be adding moisture to the area.