Solving issue of frost/moisture on inside of drywall -- Insulators' proposed solution

Brian: Sorry to hear. Can you provide any information on how the walls are insulated, and whether or not you have "cold corners" (the bottom of the insulation in the attic meets the inside edge of the wall insulation, leaving essentially nothing right in the corner)? I think you are going to hear about tearing off siding, etc, and properly insulating and air sealing. I don't think filling the cavity w/ insulation is advisable, but wait till the pros chime in.

Brian,

Looking at your photos, it seems that you have issues with the walls as well as the ceiling. We see this quite a bit with bumpouts like yours where there is a lot of framing and often non-standard sized wall cavities. The risk of poorly installed insulation goes up.

In the ceiling, the batts were likely installed before the drywall went up and it is possible that there is no insulation at all over the top plate. If that is the case, the drywall will be extremely cold, which of course is what causes the indoor humidity to condense and turn to frost.

To solve your problem, you need to air seal and insulate properly, which blown fiberglass will not do. I would recommend removing the batts and insulating the back of the drywall and all of the framing with spray foam. There doesn't seem to be a lot of room so you may want to go with a closed cell foam to get the higher r-value.

If you want to address the walls as well, they will have to be opened up. If your siding is easy to remove and put back, doing this from the outside is no big deal but if it isn't, it may be more cost effective to take down the drywall and work from the inside. Either way, the prescription is the same: air seal and insulate properly.

If your bathtub sits in the bumpout, there likely is an added benefit to tackling the walls. In standard construction there is almost never any air barrier between the tub and the outside wall sheathing, which can make the tub unusable in the winter. When we handle these jobs, we open the wall from the outside, remove the old insulation and install a suitable surface between the studs behind the tub. Then we air seal and insulate everything with sprayfoam before we caulk the frame as needed and put the wall back together again.

Brian, first of all, that's an excellent set of photos and drawings. It really helps give a sense of the construction.

I'm confused by the references to condensation in the text of your post vs. the indications of leak areas on the photos. You could develop those moisture signatures via condensation, but I would expect your house to be really, really humid, such that you have sweat on the windows that doesn't go away, or other obvious signs. Lacking that, I wonder if you have water leaking in at the bumpout roof, possibly where it meets the wall along the top of the roof slope. Your photos enlarge nicely but I can't see what the roof-to-wall flashing looks like there. The bumpout roof definitely does not appear to be vented. Do you get wind-blown rain against that wall? Any correlation between rain events and water stains showing up inside?

I doubt that we can rule out any possible cause here online without further information. If I were there I would need to carefully inspect the exterior for any possible water infiltration areas, and would need to check the interior, the crawl space, the attic, and everywhere else for signs of excess moisture. But, my hunch is that you have a flashing leak and that the insulation in the ceiling of the bumpout is fairly wet, such that it's wetting the sheetrock to the interior and conducting a lot of coldness in with it.

Did your energy auditor collect any interior humidity data, or anything else besides comment on the unusual nature of the situation?

John, Torsten, and David... thank you for the replies.

To answer your question John, the walls are insulated with a blown in fiberglass which if I am remembering correctly yields an r-15 in a 2 X 4 Wall.

Please note that the interior photos were taken the night of the frost/leaks (1/07/2010).

Weather Conditions
January 7th, 2010 (from weatherunderground.com)
High temperature 15 degrees
Low temperature 6 degrees
Precipitation T in T=Trace
Maximum Humidity 84
Minimum Humidity 51
Snow 0.10 in
Wind Speed 23mph (NNW)
Max. Wind Speed 32mph
Max.Gust Speed 41mph

We had another occurrence of moisture in the bathroom, two closets, and possibly the office soffit in the middle of January 2011 with weather conditions similar to the previous frost/condensation issues of 2010.

During these occurances we never saw any condensation on the windows. I can't say what the humidity level was in the house.

The energy auditor did collect humidity data as well as take some IR photos. I'm waiting on permission from him to post them here if necessary (I want to follow copyright since he took the photos). When he came the first time the outside temp. was 20 degrees, inside temp 70 degrees and relative humidity of 35%. The coldest interior surface from his tests was 50 degrees that day.

When he did a follow up on 2/2/2011, the outside temp. would have been between 1 and 14 degrees, inside temp. 72 degrees, relative humidity of 18% and the soffit vents to the bump out were sealed up to stop air movement coming in and there were no openings to allow air movement from the attic into the bump out.

Based on software simulating relative humidity of 40% there was an indication of the dew point being reached in the areas where the frost/moisture was initially found (the corners mainly, both inside and closest to the exterior wall) if that makes sense.

If you or anyone else has any other thoughts or more to add, please feel free. Thanks in advance.

I thought I was in zone 4A but your weather sounds much, much colder than ours. It doesn't sound likely that you had any rain at all in January 2010, or soon before that, based on the temps you are reporting. What zip code are you in?

50 degrees found on an inside surface is telling me there are serious areas in need of a fix. Outside cold air is getting in places it shouldn't be imo. You need someone local.

50 degrees found on an inside surface is telling me there are serious areas in need of a fix. Outside cold air is getting in places it shouldn't be imo. You need someone local.

Thanks again for all of the responses.

Martin: Sorry for the confusion...I really appreciate everyone's patience with me. When we have had the frost/moisture in the bump out we have also had it in the cantilever in the office (it hasn't happened any other times). I have attached a better picture of this as well as indicated where areas of moisture have occured.

What problems could occur with an unvented roof assembly with fiberglass packed completely? They do plan on leaving the holes they cut in the attic to add the insulation open so there would be some openings to the attic space. The insulators informed me that if this didn't work they would come back out to try something else. No matter what is done to remedy the situation I plan on having the energy auditor back out to recheck the areas to test the results. Again, thank you for your replies. They are greatly appreciated.