Expert: Ted Barnhill (Principal, Design45 LLC) - 12/5/2007

Question
QUESTION: I have a new home one story ranch built in 2006. In the winter I notice moisture up in the corners where the ceiling and walls meet in a certain part of the house. This only happens when the temperature suddenly drops drastically say from 50 to 20 degrees. If it stays steady even if cold for a few days it will dissappear. Do you have some ideas as to what may be happening?

ANSWER: Rod,

Moisture in homes is a complicated issue, and has resulted in many changes in accepted building practice over the past two decades (not to mention more than a few lawsuits).  Your mystery moisture sounds like condensation, but the source and solution may not be simple to diagnose and correct.  

Does the moisture appear as droplets on the surface of the wall, or is the wallboard soggy, as if soaked from behind?  Is the wall at that location particularly cold?

It may be that the moisture in your home's indoor air is condensing directly on a very cold wall.  It is common for blown insulation (or some batts) to settle down in the walls, leaving colder spots at the top.  As the overall humidity level in your home drops with extended cold weather, the condensation would taper off.

It could also be that your attic isn't well ventilated, and the moisture in the trapped air is condensing on cold surfaces like the roof sheathing, and dripping down onto your ceiling at the roof/wall joint.  A situation like this is a common type of moisture problem.  Often, badly-sealed (or unsealed) exhaust ducts, recessed lights, junction boxes, etc. allow warm (relatively moist) air from the home to enter the attic and condense there, continuously dripping back onto the ceiling and walls.  The fact that your moisture goes away is a good sign, but still a potentially serious source of mold and rot.

I suggest that you contact the builder; he/she may accept responsibility for this problem as a warranty matter on such a new home.

Good luck, and feel free to follow up with me.  -Ted

---------- FOLLOW-UP ----------

QUESTION: Ted...yes it appears as soggy more like being soaked from behind and is on the side of the house where the cold wind hits. As I said...it only does this when there is an extreme drop in temperature and appears mainly in upper corners where the walls meet the ceiling. Some condenstation is on the ceiling and some a few inches down the wall. After a few days it dissappears if the temperature remains stable...even if cold. Seems like it stays around though for a while in extreme cold...like teens or single digits.  A couple of days ago it went from 60 degress down to about 32 in a matter of a few hours (midwest weather) and it showed up. A licensed inspector is currently working on locating the problem but would be open to suggestions or theories. Sounds like you may be familiar with what I have described. He did say something similar to you regarding the insulation in the walls. He had one theory regarding the ventilation in the attic. It has a ridge vent and gable end vents which he said was not the norm. Usually one or the other I think he said. Could that be causing anything? Thanks for your information.

Answer
Rod,

Glad to hear that you have an expert looking at it.  It does sound like a problem of condensation in your attic.  To resolve it, you will want to:

1. Properly ventilate your attic.  This means soffit vents (for air to enter), as well as ridge/gable/button vents (for air to exit).  It is fine to have both gable and ridge vents, but they don't replace soffit vents.  Depending on the heel of your truss, you may need vent chutes installed under the roof decking, above the wall/ceiling joint.  This holds your insulation away from the decking to maintain ventilation.

2. Seal any ceiling openings in your home to prevent moist air from moving into the attic.  This includes junction boxes, recessed cans, and especially bath vents or heat ducts that run in the attic.

Good luck, Ted