Condensation—Are You Seeing Spots?

When it gets this cold and this warm all at once...

Water spots appearing on textured ceiling

When a number of our former clients starting calling us about water spots appearing in their ceilings we were a bit perplexed since in most of the cases we hadn’t done any work on the roof or the attic and none of the homes were in the recent path of the hail storms that whacked the metro area last year.


“In cases of winter water leaks like this there can be a number of causes,” explains Murphy Bros. owner John Murphy. “It could be a leaky roof flashing detail, a poorly flashed chimney, a cracked roof vent and so on, but when it happens suddenly on the first warmer days after an extended cold snap, our first thought is condensation.”

As in these recent cases, the spots were all over the ceiling and appeared suddenly without any rain or snow involved. So how is condensation involved?


Water spots on ceiling where condensation drips through insulation and cracks or holes in vapor barrier


“That sudden swing in temperature, from three steady weeks of below zero to 40 above in just a day or two is the key to this mystery,” John explained. “At least in these cases we’ve seen recently, the appearance of water in the ceiling is the result of condensation build up on the roof trusses and sheathing, and the sudden melting of that moisture when the temps quickly climb well above freezing.”


“Think of your attic like a giant vacuum, sucking air and all the moisture in that air up from the rooms below. The colder the attic air is, the greater the temperature differential, and the stronger the vacuum action. Add to that any cracks in seams or around vent pipes, electrical wiring, and soffits in older homes and with all that additional cold air and you have the perfect storm when it comes to condensation. It just keeps building up over time until it thaws. If the thaw is slow, evaporation will take care of most of that melt. But with a quick and dramatic thaw like we just had, then you’ve got water dripping down through the insulation, finding it’s way via pin holes and cracks into the ceiling,” concludes John.


The difference between evaporation and condensation.


In some cases the water spots will dry out and disappear. However, to prevent this in the future, (not that it will ever get mind-numbingly cold again) make sure your ceiling envelope is tight, your attic is vented and airflow is adequate. It is important then that all pipes and small penetration of any kind need to be foamed shut. Ducts for bath and kitchen vents should be insulated and wrapped in a vapor barrier. Attic chutes should be added or fixed and a windwash barrier should be secured on perimeter walls. Lastly, an additional 4 or more inches of so of cellulose insulation should be blown over the existing insulation in the attic so that a minimum R-Value of 44 is achieved, but we would recommend R-60 for a maximum ROI over time.

We also recommend using blown in cellulose for as it is very cost effective, has a greater R value per inch than most other attic insulation which means more protection in areas that can't fit a lot of volume such as near the wall lines where the roof slopes down. Cellulose also has a higher density than fiberglass insulation which minimizes air movement through it on windy or very cold days and creates a more effective blanket over the heated areas of your home.

“And until you get your attic upgraded, you might want to limit that 20-minute shower to 10 on the same day you cook a pot of spaghetti and give the dog a bath.” “Or,” says John, “You could just move to Florida!" On some days, when the wind chill is in the negative double digits for weeks on end, that really sounds like a good idea.


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